4 Building Your Presentation

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What considerations should go into producing the content of your presentation? Although the specifics are dependent on your topic, several general considerations are critical.

4.1 The Target Specifications

As engineers, we can’t design a product without specifications. Similarly, as technical speakers we can’t design a presentation without a clear picture of the specifications we’re trying to meet. One sensible breakdown is as follows.

1. The subject material. What is the scope of your presentation? Which topics do you wish to cover (or need to cover), and at what depth?

2. The audience. To whom will you be speaking? What are their backgrounds and purposes?

3. The time length. How many minutes or hours will you have? Will the limit be strictly enforced? If the presentation lasts for hours, when will breaks be taken?

4. The venue. In what environment will you be speaking?

(a) Indoors? Outdoors?

(b) What are the acoustics and lighting situations like?

(d) What sorts of equipment will be available?

Now is the time to answer as many of these questions as possible. The issues we have listed can vary markedly from one situation to the next. Don’t make the mistake of assuming that the variables pertaining to your last talk will carry over to your next one.

Example. Larry was told that he would be giving a review of his recent project to one of the vice presidents. “OK, know your audience,” he thought to himself. “The top brass don’t like a lot of detail, so I’ll just concentrate on the big picture.” Then, he joked, “And use small words!” Larry couldn’t have been more wrong. It turns out that this VP is a former engineer, and in fact had helped design the original product that Larry was now working to improve. Larry’s presentation was a disaster. Afterwards he talked with a colleague who said, “This VP demands a lot of technical content. He wants to make sure you have the capabilities to handle the task. I wish you had talked with me first.” Larry learned that know your audience isn’t just a platitude, and that a little research can prevent painful misunderstandings.

4.2 Quality Control: Some Key Aspects

Good technical speakers put forth arguments that are logically sound. Their English is vivid, accurate, and appropriate; their math is clear and correct. They come equipped with effective, attractive visual aids. And they always bear in mind the ethics and potential legalities of a situation.

Example. Sara gave a stunning technical talk about automotive communication systems, but failed to disclose her relationship as a paid consultant for one of the major car manufacturers. Later she was accused of a breach of ethics for harboring a conflict of interest.

Your presentation will only be as strong as its weakest link. In the next few sections we provide some pointers about the diverse aspects of presentation quality.

4.3 Logic

Although logic is an extensive and beautiful subject worthy of study for its own sake, our interest is to prevent silly (or catastrophic) logical blunders. In speech as in writing, people commit two main types of logical mistakes or fallacies: formal and informal. Let’s examine each of these in turn so you can avoid them.

Formal Deductive Fallacies

Formal fallacies violate basic, accepted patterns of formal reasoning. One such pattern is the classic categorical syllogism illustrated by the argument

All men are mortal.

Socrates is a man.

Therefore, Socrates is mortal.

The first two statements are the premises (or assumptions) and the third is the conclusion. The argument is valid not because the conclusion holds, but because the truth of the conclusion must follow from that of the two premises. Any argument of the general form

All S are P.
x is an S.	✓ valid
Therefore, x is P.

is valid for the same reason. In Figure 4.1 we use diagrams to check this. The same syllogism may appear in abbreviated fashion:

All men are mortal, so Socrates is mortal.

Socrates is a man, so he is mortal.

FIGURE 4.1

A categorical syllogism. (a) Concrete case. Socrates is a man, and all men are mortal. So Socrates is mortal. (b) Abstract case. The point x falls within the set S, which in turn lies within a set P. Clearly x must fall within P.

In each case one of the formal premises is left implied.

Example. While giving a talk on chemical safety, Caroline stated:

Arsine is a Cat 1 toxin. It can kill you.

This argument takes the form:

All Cat 1 toxins are substances that can kill you. (All S are P.)

Arsine is a Cat 1 toxin. (x is an S.)

So Arsine is a substance that can kill you. (Therefore, x is P.)

Since the premises are true, and since the argument is a valid syllogism, the argument is sound. As you can imagine, it had a powerful effect on Caroline’s audience.

Now let’s examine a couple of fallacious arguments. Consider

All X is Y.
y is Y.	× invalid
Therefore, y is X.

and examine Figure 4.2(a). This argument form is not valid: the point y shown in the figure is an invalidating counterexample, and it takes only one of these to wreck the argument. The argument form

All Y is X.
No Y is Z.	× invalid
Therefore, no Z is X.

is invalidated by the counterexample x in Figure 4.2(b).

Example. While giving his thesis presentation on microwave measurements, Joseph said:

There are many types of RF connectors, but all are precision connectors. This is because 3.5 mm connectors are precision connectors, and some RF connectors are 3.5 mm connectors.

Several audience members winced at his conclusion that all RF connectors are precision connectors. They knew that it was not true, regardless of his contorted logical argument. A little careful analysis would lead Joseph to the underlying form of his argument (see Figure 4.3):

All 3.5 mm connectors are precision connectors. (All T is P.)

Some RF connectors are 3.5 mm connectors. (Some R is T.)

So all RF connectors are precision connectors. (So all R is P.)

Both premises are true, so what went wrong? This is another example of an invalid categorical syllogism, so Joseph’s argument is invalid.

FIGURE 4.2

Two invalid syllogisms. (a) Everything that has the attribute X also has the attribute Y. However, the additional assumption that y has the attribute Y does not imply that it must have the attribute X. (b) The assumption that Z and Y are disjoint does not imply that Z and X are disjoint. An element x can belong to both Z and X.

In many ways, speakers must be quicker in their thinking than writers. As they don’t have the luxury to stop and ponder over their statements, they must be adept at quickly analyzing the logic of their own arguments. A sturdy grasp of logical argument will help you avoid many embarrassing blunders. For convenience, we have provided a list of valid categorical syllogisms in Exercise 4.6.

Arguments Based on Conditional Statements

Not all reasoning patterns are based on categorical syllogisms, so we must cover a few more ideas. From now on, unless otherwise stated, uppercase letters such as P and Q will denote statements rather than classes of objects. So P could be

the area of a circle having radius r equals πr²

which is a true statement, and Q could be

FIGURE 4.3

Joseph’s logical blunder. T lies completely within P, and some of R lies within T. But it does not follow that all of R must lie within P, as demonstrated by counterexample x.

−14.8 is a positive integer

which is a false statement. A compound statement of the form

If P, then Q.

is a conditional statement; the statement P is its antecedent and Q is its consequent. Take a moment to memorize these terms; they are standard and will occur repeatedly in the next few pages.

Example. Consider the conditional statement:

If I am a licensed professional engineer, then I have a college degree.

Let’s break it down:

If I am a licensed professional engineerantecedent, P, then I have a college degreeconsequent, Q. $If \underset{antecedent, P}{\underset{︸}{I am a licensed professional engineer}}, then \underset{consequent, Q}{\underset{︸}{I have a college degree}} .$

Note that we are not free to interchange the antecedent and consequent of a conditional statement without a (possibly drastic) change in meaning.

Example. The statement:

If I have a college degree, then I am a licensed professional engineer.

is clearly false; as valuable as a nursing degree may be, it does not grant licensure as a professional engineer. This statement is called the converse of the statement in the preceding example.

We now examine some argument forms involving conditional statements. Please don’t be discouraged by their technical sounding names. Arguments of these forms are recognizable in all engineering discourse.

Modus Ponens, or Affirming the Antecedent

The pattern

If P, then Q.
P.	✓ valid
Therefore, Q.

is a standard argument form called modus ponens. Since the antecedent of the conditional in the first premise is affirmed by the second premise, the form is also called affirming the antecedent.

Example. The argument:

If my presentation is bad, I won’t get the contract. My presentation is bad. So I won’t get the contract.

takes the form of modus ponens. It is a valid argument.

Modus Tollens, or Denying the Consequent

The following pattern is a standard argument form called modus tollens. By not-Q, we mean the statement called the negation of Q.

If P, then Q.
Not-Q.	✓ valid
Therefore, not-P.

In English we can negate a statement by appending It is false that to the start of it, although this may not yield the most concise or graceful formulation.

Example. The statement:

All keynote speakers are college professors.

is false. Its negation can be phrased in any of the following ways:

It is false that all keynote speakers are college professors.

Not all keynote speakers are college professors.

Some keynote speakers are not college professors.

There is at least one keynote speaker who is not a college professor.

The negation of a false statement is true, and the negation of a true statement is false. Let’s get back to modus tollens. Since the consequent of the conditional in the first premise is denied by the second premise, the form is also called denying the consequent.

Example. The argument:

If my presentation exceeded 30 minutes I would have been stopped by the moderator. I was not stopped by the moderator. Therefore my presentation did not exceed 30 minutes.

takes the form of modus tollens. It is a valid argument.

An Argument Form with Two Conditional Premises

Here’s another standard reasoning pattern, this time with conditional statements for both premises.

If P, then Q.
If Q, then R.	✓ valid
Therefore, if P then R.

Example.

If my abstract exceeds one page, it is rejected. If my abstract is rejected, I cannot present my paper at the conference. So, if my abstract exceeds one page, I cannot present my paper at the conference.

Fallacies Involving Conditional Statements

What can go wrong with arguments containing conditional statements? There are two famous fallacies to guard against. The first is called affirming the consequent.

Example. The argument:

If my abstract is not properly formatted, it is rejected. My abstract is rejected. Therefore my abstract is not properly formatted.

is not modus ponens. The antecedent of the conditional (“my abstract is not properly formatted”) is not affirmed in the second premise; rather, the consequent (“it is rejected”) is affirmed. This argument is invalid. (There may be many reasons for rejecting an abstract other than formatting.)

In general, an argument of the following form is fallacious.

If P, then Q.
Q.	× invalid
Therefore, P.

Again, this is called affirming the consequent. Let’s proceed to the second fallacious form.

Example. The argument:

If this is Tuesday, we have a review meeting. This is not Tuesday. Therefore we do not have a review meeting.

is not modus tollens. The consequent of the conditional (“we have a review meeting”) is not denied; rather, the antecedent (“this is Tuesday”) is denied. This argument is invalid. (Maybe review meetings occur on both Tuesdays and Fridays.)

In general, an argument of the following form is fallacious.

If P, then Q.
Not-P.	× invalid
Therefore, not-Q.

This is called denying the antecedent.

The Disjunctive Syllogism

Another valid argument form, commonly seen, is the disjunctive syllogism. The pattern is

P or Q.
Not-P.	✓ valid
Therefore, Q.

The first premise guarantees that at least one of the statements P and Q must hold. This, taken together with the second premise (that P does not hold), is enough to guarantee that Q holds.

Example. The argument:

Either the presentation is canceled or I am in the wrong room. The presentation is not canceled. Therefore I am in the wrong room.

takes the form of a disjunctive syllogism. It is valid.

Informal Fallacies

The fallacies presented above are examples of formal, deductive fallacies. Another part of logic, called informal logic, collects and classifies other types of fallacies that commonly occur in human discourse. People have committed these types of errors intentionally or unintentionally since the time of Aristotle (384 – 322 BCE). Avoid them all.

Ad Hominem

This fallacy occurs when someone attacks a person rather than his argument.

Example. Henry is giving a presentation to several managers and engineers to convince them to start using a new process he has developed.

I know Dan argues that this new process is less efficient than the current one, but you know Dan. He’s never willing to try anything new. He’s always stuck in the past.

It may be that Dan is excessively cautious, but that does not discredit his arguments regarding the new process.

Fallacy of Accident

This fallacy occurs when someone applies a rule to a case it was not intended to cover.

Example. Previously we told the story of Larry, who had heard that the top brass only want the “big picture” and that one should never bother them with details. Larry fell victim to the fallacy of accident when he applied this rule to a VP who himself was an engineer. His logic went something like this: (1) bigwigs don’t want to hear about technical details; (2) the VP is a bigwig; (3) he won’t want to hear about details. Larry was caught applying a rule of thumb (bigwigs don’t like details) where it isn’t appropriate — in this case thinking a bigwig who is an engineer won’t want to hear technical details. Sometimes called a “sweeping generalization,” this fallacy can cause us headaches when we apply rules of thumb to situations where they are not valid. Engineers are particularly vulnerable when they learn about rules without knowing their limitations.

Straw Man Fallacy

This fallacy occurs when someone distorts a person’s position and then attacks the distorted version.

Example. Allen was presenting his ideas to his manager about a new annealing process he had devised to strengthen beryllium alloys. His colleague, Mannie, had proposed instead that the company should use Klingman’s process, a phase transition approach accepted industry-wide. Allen knew that to get his manager to buy into his idea he would have to provide a good reason, so he decided to attack Mannie’s position.

Everyone knows that phase-transition processes are just too expensive! Look at Johnson’s process — no one uses that anymore because it costs too much.

His manager jumped in:

Wait a minute. Mannie never said he wanted to use Johnson’s process. It has nothing to do with annealing!

Allen had used Johnson’s process as a straw man to attack Mannie’s idea; unfortunately for Allen, his manager caught on right away.

Appeal to Ignorance

This fallacy occurs when someone gives up on further thinking and investigation. They might say, for instance, that event A must have caused event B because they cannot imagine any other reason for the occurrence of B.

Example. In Clara’s first conference presentation, she examined the proposition (suggested by some in industry) that coating a waveguide tube with carbon can prevent unwanted microwave oscillations. Her theoretical analysis showed that this approach generates too much loss, and her last slide asserted that:

Coating the tube with carbon is not a viable option for eliminating oscillations.

The very next speaker started his talk with:

The last speaker gave a great argument of why carbon can’t be used to suppress oscillations. Now I’ll show you how we did it.

He went on to show how, by slightly altering the pattern of carbon, the loss could be reduced significantly and the oscillations eliminated. Clara was mortified and has never forgotten the lesson. You can’t assume a proposition is false just because no one has proven it true (or vice versa).

Hasty Generalization

This fallacy occurs when someone makes an inference about all members of a group from the characteristics of an insufficient sample.

Example. Tim is a graduate student in chemical engineering who has now given two conference presentations. Both presentations were at the same conference. His colleague Penny was to give her first talk at a conference that, although similar in theme, was different than the one Tim attended. Tim said:

The best thing about these conferences is that you can use your own computer to do the presentation.

Penny brought her computer, but was horrified to discover that presenters were required to use a specific system she had not prepared for. Fortunately she was able to get emergency help in adapting her presentation materials for the new system. Tim lacked sufficient experience with conference presentations to make a general statement about the procedures at all conferences. Be sure to do your homework!

Post Hoc Ergo Propter Hoc

This fallacy occurs when someone concludes that event A must have caused event B because A preceded B in time.

Example. In his master’s defense, Isaac was faced with the need to explain why some of his measurements were considerably worse than others. He had noticed that all of the “bad” measurements were made after the installation of a new balance.

I’m pretty sure that the cause of my problems is an improperly calibrated balance. It can’t just be a coincidence that all my troubles started after it was installed.

In fact, it was just a coincidence, and his adviser let him know it:

Wait a minute! I had that balance calibrated right after installation. We have since used it in many measurements, and all have turned out well. Think again!

Isaac should have given this issue more thought before his presentation. Just because the balance was installed before his measurements went bad, doesn’t mean it was the cause of his troubles.

Cum Hoc Ergo Propter Hoc

This fallacy occurs when someone concludes that event A must have caused event B because A and B occurred simultaneously.

Example. Bill really put his foot in his mouth when he made this statement during a briefing on his project:

Our funding got cut when the Division budget got reduced, and this is making it really hard to complete the project.

His boss jumped in:

You didn’t get your funding cut because of this! Rather, your progress was too slow and so we decided to cancel your project. Had you done well, I would have protected you from the budget reductions!

Ouch.

Fallacy of Composition

This fallacy occurs when someone erroneously attributes a trait possessed by all members of a class to the class itself.

Example. Aubry fell victim to the fallacy of composition when she gave a talk about sintering at a regional meeting of professional engineers. During the rehearsal for her talk, she received feedback that she should slow down and provide additional detail when describing the flowchart for the sintering process. This worked so well that Aubry hastily decided (during the presentation) that what’s good for one slide should be great if applied to every slide. Unfortunately she failed to consider the aggregate increase in time that changing her pace would incur, and she exhausted her allotted time before reaching the halfway point in her talk. While it probably would help on any one slide to slow down a bit, slowing her pace on the whole talk was a disaster.

Fallacy of Division

This fallacy occurs when someone erroneously attributes the traits of a class of objects to each of the separate objects.

Example. While presenting her senior project, Donna claims that the dipole antenna used in her communications link has a high gain. She is quickly corrected by her instructor, who notes that a dipole has a relatively small gain.

But the claim of the manufacturer I read said that dipoles have large gain.

After much back and forth, the instructor finally teases out that Donna has used one element from a large antenna array. While the array itself has high gain, each element has relatively low gain. The gain is high only when the elements act together.

Begging the Question

This fallacy occurs when someone uses their target conclusion as one of their premises.

Example. Carlos made the mistake of begging the question during his dissertation defense, when he made the statement:

This chemical is highly acidic because it has a low pH.

This led to a lengthy discussion of whether Carlos really understood the chemical he was studying. In essence, Carlos made the argument that “the chemical is acidic because it is acidic,” and this was not very convincing to his examining committee.

Weak Analogy

This fallacy occurs when someone argues based on an alleged similarity between two situations that, in reality, are not that similar.

Example. Analogies are a great way for a speaker to connect with her audience, but care is required to make sure that such analogies do not lead to incorrect conclusions. For instance, to help the audience visualize ductility, Belinda could say during a talk on the strength of materials that:

Gold stretches when pulled, just as rubber does.

But for her to conclude that “gold and rubber must have similar underlying structures” would be silly.

False Dichotomy

This fallacy occurs when someone bases an argument on the premise that either A or B must hold, when in reality a third possibility C could hold.

Example. During her project presentation in a mechanical engineering class, Pam’s instructor tried to fluster her by trapping her in a false dichotomy.

Is the mass in a state of stable or unstable equilibrium?

She refused to be nonplussed and responded:

It’s not in equilibrium at all. The mass is accelerating.

Pam avoided being trapped in a fallacy.

Fallacy of Suppressed Evidence

This fallacy occurs when someone omits counterinstances while drawing an inductive conclusion.

Example. Rob presented the results from his study of automobile accidents to a safety review panel. The issue was whether the failure of a part manufactured by his company was at fault in a string of collisions. He quoted heavily from research done at a local university, and at the end of his talk summarized his findings.

The evidence does not support the hypothesis that the failure of the coupling caused the accidents under investigation.

One panelist was not satisfied.

You completely overlooked two studies done by the National Safety Institute. I think when you consider their findings, your conclusion will be quite difficult.

Scientists and engineers must always refrain from “cherry picking” their results. If you don’t trust certain results, don’t dismiss them, but instead explain to the audience why you find the results questionable.

Fallacy of Equivocation

This fallacy occurs when someone uses a word in two different ways in the same argument.

Example. Jenny had an embarrassing moment during her project presentation for her class on fermentation when she was asked why she didn’t purge her system. Wasn’t she worried about Henry’s law?

We didn’t think it applied to us because we checked the local statutes and couldn’t find it listed anywhere.

Jenny had confused “scientific law” with “legal regulation.”

Fallacy of Amphiboly

This fallacy occurs when someone argues based on a faulty interpretation of an ambiguous statement.

Example. It is easy to perplex an audience with poorly constructed statements. Consider the audience’s confusion over George’s statement:

I decided to do the error analysis after I looked at the results.

Did he mean

1. “After I looked at the results, I decided I should do the error analysis,” or

2. “I decided that I should look at the results, and then do the error analysis.”

The difference could be significant.

Appeal to the Crowd

This fallacy occurs when someone argues that statement A must be true because most people believe it’s true.

Example. During Annette’s thesis defense, she was asked why she calibrated her system at the end of the experiment and not at the start. Her reply was:

Everybody in our group has been doing it that way forever. They can’t all be wrong.

Yes, they can. It turns out that once one person had calibrated the system improperly, everyone else followed suit.

Fallacy of Opposition

This fallacy occurs when someone argues that statement A must be false because their opponent believes it’s true.

Example. Martin assessed a potential new process in a briefing to his boss:

If those guys at Cromwell Machines are using the process, then I wouldn’t put too much faith in it. We can always do better than them. Let’s use another process.

It may turn out that this is the best process to use, and Martin shouldn’t be so quick to dismiss it without solid evidence.

The fallacy of opposition often leads to missed opportunities. Factions form within companies, within universities, within research groups. Just because someone is your competitor, doesn’t mean you are right and they are wrong.

Appeal to Authority

This fallacy occurs when someone argues that statement A must be true because experts believe it’s true.

Example. There’s no doubt that quoting an expert during your presentation can lend credence to your argument, but don’t forget that even the “experts” can be wrong. Consider what the great physicist Niels Bohr once said:

An expert is a person who has found out by his own painful experience all the mistakes that one can make in a very narrow field.¹

Be sure you have corroborating evidence.

Additional Ways to Check for Errors

The following approaches should be familiar to any engineer.

Intuitive Plausibility

Is the result reasonable? This question can save us much embarrassment in front of an audience.

Example. While generating numerical data for a presentation, we notice that when the temperature in our model is reduced, the thermal radiation is increased. Perhaps we should look for an error in our calculations.

Dimensional Checks

Physical dimensions must match across all terms in a valid physical equation.

Example. Suppose we write:

The maximum height of a projectile launched from an initial height h₀ at an angle θ with velocity v is given by

h = h0 + v2sin2θg $h = h_{0} + \frac{v^{2} \sin^{2} θ}{g}$

(1)

where g is the acceleration due to gravity.

The physical dimensions in (1) are analyzed as

[length]=[length]+[length]2[time]2/[length][time]2 $[length] = [length] + \frac{{[length]}^{2}}{{[time]}^{2}} / \frac{[length]}{{[time]}^{2}}$

and thus both terms have the same dimensions of [length]. This is necessary for the equation to be correct, but it is not sufficient. It doesn’t help us learn whether there is a missing term, or if the power on the sine function is correct (since the sine function is dimensionless). Even so, a dimensional check is a valuable method for finding errors.

Example. If x and y have units of length, then the equation

x=cos y $x = \cos y$

is wrong for two reasons. The cosine function is dimensionless and so the dimensions cannot match across the equals sign. Additionally, the cosine function is required to have a dimensionless argument.

More practice with dimensional checks is provided in Exercise 4.7.

Order-of-Magnitude Checks

Quantitative claims should be numerically reasonable.

Example. Marie’s senior project group is preparing for their final presentation. She has been assigned the task of estimating the distance that a potato will travel when launched by a pneumatic potato gun. She plugs numbers into the equation

d = v2sin(2θ)g $d = \frac{v^{2} \sin (2 θ)}{g}$

and obtains the answer 1 × 10¹³ m. This seems a bit large to her, being greater than the distance from the earth to the sun. A quick check reveals that she has used “big G” (the universal gravitational constant) instead of “little g” (the free-fall acceleration constant) in her calculation. Recomputing with the correct constant, she finds d = 70 m, a much more reasonable result.

Expected Variation with a Parameter of the Problem

Some quantities in a problem may be denoted by letters but temporarily held fixed during a calculation involving other variables. We call these quantities parameters.

Example. The equipotential surfaces for a small electric dipole centered at the origin and aligned along the z-axis are given by the equation

r = cvcos θ−−−−√. $r = c_{v} \sqrt{\cos θ} .$

Here r is the distance from the origin to the surface at an angle θ measured from the z-axis. This equation describes a family of surfaces: one for each value of c_v. To plot one equipotential surface from the family, we might set c_v = 2 and plot r = 2cos θ−−−−√ $r = 2 \sqrt{\cos θ}$ . To plot another surface, we could set c_v = 3. While plotting each surface of the family, we are holding c_v constant. However, c_v is neither a “true” constant like e or π nor a variable like θ; it is an example of a parameter.

Often an answer may be checked by varying parameters and validating against known behavior.

Example. Consider a simple problem from introductory physics. A particle carrying charge Q is fixed at the coordinate origin, while a second particle of charge q is moved from radius b to radius a in its presence. If b > a then the work required to move the second particle is given by the integral

W=−∫abF→ ⋅ dℓ→=−∫ab14πϵ0qQr2dr = qQ4πϵ0 (1a−1b). $W = - \int_{a}^{b} \vec{F} \cdot d \vec{ℓ} = - \int_{a}^{b} \frac{1}{4 π ϵ_{0}} \frac{q Q}{r^{2}} d r = \frac{q Q}{4 π ϵ_{0}} (\frac{1}{a} - \frac{1}{b}) .$

We can check this answer in several ways. If we increase either q or Q, the amount of work required increases since the force between the particles increases. This makes sense. If we increase b, the work required increases because we have to move the second particle farther. Again, this makes sense. Finally, if we decrease a, we again need more work to move the second particle farther.

As engineers, we should always be thinking this way. Using logical reasoning, we would easily catch an integration error leading to

W=qQ4πϵ01ab√ $W = \frac{q Q}{4 π ϵ_{0}} \frac{1}{\sqrt{a b}}$

even though the dimensions are correct!

The above example shows the value of solving problems using parameters. We could have considered a fixed 5 C charge, and moved a 3 C particle from a radius of 2 m to a radius of 1 m, thereby considering just one specific case. Instead, by using parameters, we obtained a formula giving the work required to move between any two points for any two charges.

Agreement with Known Special Cases

One advantage of working problems in terms of parameters is that a problem may have limiting cases whose answers are known.

Example. Say that you are required to find the stopping distance of an automobile when the brakes are locked while the vehicle is traveling uphill. You easily find the formula in a handbook for the case when the vehicle is braking on a flat surface:

D=v202gμs $D = \frac{v_{0}^{2}}{2 g μ_{s}}$

where v₀ is the initial speed, g is the acceleration due to gravity, and μ_s is the coefficient of friction for the tires against the road. But, try as you may, you can’t find the formula for a car traveling uphill. So you oil up your rusty calculus skills and derive the following formula:

D = v202g(μs + tanθ) $D = \frac{v_{0}^{2}}{2 g (μ_{s} + \tan θ)}$

where θ is the incline angle. Is this correct?

First you check the dimensions. Since both μ_s and tan θ are dimensionless, adding them is allowed and the dimensions check out OK. Next you decide to use some physical reasoning. If you increase the angle θ the car should decelerate and stop in a shorter distance. Sure enough, increasing tan θ decreases D. Finally, you check against the known special case and let θ go to zero for a flat incline. Since tan θ also goes to zero, your formula does reduce to the special case you found earlier. This gives you a lot of confidence that your answer is correct, but there is no guarantee that you did not make an error. For instance, the formula

D = v202g(μs + tan2θ) $D = \frac{v_{0}^{2}}{2 g (μ_{s} + \tan^{2} θ)}$

passes all three of the same tests. Nevertheless, checking for agreement with known special cases is always a good idea. It represents another tool you can use to hunt for errors in claims before you show them to the world during your next technical presentation.

You can also run checks by approximating an answer: dropping small terms, ignoring slow time variations, etc. These and many other useful techniques receive extensive coverage in the standard engineering curricula.

Other Mathematical Properties of the Answer

If an answer is time dependent, you might check its initial value, its final value, or its time-average value.

Example. Suppose your answer for the voltage in a circuit is

v(t) = 5 + 10e−5tcos 20 t V. $v (t) = 5 + 10 e^{- 5 t} \cos 20 t V .$

The initial value of v(t) is v(0) = 15 V, and the final value is v(∞) = 5 V. If either of these seems wrong, you should check your calculations.

Mathematical answers sometimes contain features such as infinite singularities and jump discontinuities. These are often (but not always) inappropriate from a physical standpoint.

Example. The displacement of a drum head in natural oscillation can be found by solving the wave equation. Proceeding along purely mathematical lines, the displacement is found to be proportional to the term

AJm(λmnr) + BNm(λmnr). $A J_{m} (λ_{m n} r) + B N_{m} (λ_{m n} r) .$

Here r is the distance from the center of the drum head, λ_mn is the vibrational parameter for the (m, n) mode, and J_m(x) and N_m(x) are the Bessel and Neumann functions. However, from physical reasoning it is inappropriate to retain the Neumann function, even though it is a proper mathematical solution. Since N_m(x) becomes infinite as x → 0, this term must be discarded. After all, it makes no sense for the displacement of the drum head to become infinitely big at the center!

Accord with Standard Physical Principles

Notions like causality and symmetry are encountered routinely in the physical and engineering sciences. Why not use them to look for errors whenever possible?

Example. An electric circuit is excited for the first time at time t = 0, and you calculate the voltage as

v(t)=V0e−10|t|. $v (t) = V_{0} e^{- 10 | t |} .$

This result looks promising since the voltage decays to zero as time increases to infinity. However, you quickly realize that the voltage exists for time t < 0, which is before the excitation was applied. Because this violates the principle of causality, your formula cannot be correct.

Another important principle is superposition, although one must remember that it applies only to linear systems.

Example. Always check to see whether the whole is greater than the sum of its parts. When adding sinusoidal signals, for instance, the amplitude of the resulting sinusoid can be smaller than the sum of the individual amplitudes, but it can never be larger. Similarly, in linear media, two strong waves may come together and cancel each other by destructive interference, but they may never add to a wave ten times as big as the larger of the two.

Other Ways to Be Careful

Follow these suggestions to avoid sloppiness and prevent errant claims.

• Don’t jump to conclusions.

• Maintain a critical attitude.

• Respect the truth.

• Employ Ockham’s razor.

• Insist on reliable evidence from dependable sources.

• Double check everything.

• Always seek counterexamples to your claims.

See the authors’ book Engineering Writing by Design: Creating Formal Documents of Lasting Value for expanded treatment of the points in this list.

Example. The post hoc ergo propter hoc and cum hoc ergo propter hoc fallacies can rear their ugly heads when inappropriately linking cause and effect. Remember that correlation does not imply causation. The fact that your team won the big game when you were wearing your shirt backwards is no reason for you to do the same during every game. As an engineer, you probably wouldn’t fall victim to such a silly superstition (would you?). However, if you notice that those pesky oscillations disappeared when you lowered the manifold temperature, you should probably run a sequence of controlled experiments before deciding that there is an actual relationship between the events.

4.4 English Usage

Crucial among the building blocks of any technical presentation are the words the speaker uses and how they are connected together.

Word Choice

Some words may appear on your slides and some may be “merely” spoken, but they are all important and worthy of careful selection. The right choice of words will take into account two issues:

1. correct technical meaning, and

2. proper level of formality for the occasion.

A technical presentation is not the time or place for sloppy diction. Informal terminology, slang, cute spelling, and internet jargon are not appropriate in a formal presentation, unless specifically relevant to the topic under consideration. Acronyms or specialized terms need to be written out or explained. Remember that clarity of presentation is key.

Example. Anna, a young engineer at a large electronics firm, was making her first presentation at a program review meeting. She was used to sending out quick, informal briefings to her teammates through e-mail, but now had to describe their recent progress to her manager and his staff. She gathered together her briefings and put them into a short presentation. One slide, an update on the progress of the computer coding, contained the following bullet points:

• Pam said to give her a hedzup B4 we start coding — she’s going PLOA

• Joe said to do up the interface design first, and then handle the coding l8tr

• I suggested we aughta use Git for sharing code. This really rox!

• Next step — we hafta integrate across platforms, IMHO.

As you might expect, Anna’s boss reacted to this lack of professionalism with a combination of confusion, embarrassment, and disappointment.

Correct spelling is a must. When in doubt, always consult a reliable dictionary.

Example. Beware of words that look alike or sound alike. Sometimes a spell checker isn’t enough. Imagine having these on your slides:

We used aesthetic acid.

The break pads were warn.

It will consume an energy of 10 dines.

Water friezes at 0 degrees Centipede.

The you-bolts were the week lynx.

We use sigh to represent the angel in poler coordinates.

And, although this may seem obvious, be sure you can actually pronounce all the words on your slides!

Example. In the heat of a cut-and-paste session, Brett included the word algorithm on one of his presentation slides. Imagine everyone’s discomfort when, during the actual event, Brett took several stabs at saying this word before giving up. He knew what an algorithm was. But different levels of familiarity with words are possible — the fact that you can recognize a word doesn’t mean you can say it correctly … especially with 50 people staring at you.

A list of commonly mispronounced words is given in the table below. The phonetic translations are ours, and use the 40 phonemes of the system Truespel (http://www.truespel.com/en/).

word	incorrect pronunciation	correct pronunciation
across	u-krausd	u-kraus
arctic	aar-tik	aark-tik
asterisk	as-ter-iks	as-ter-isk
athlete	athh-u-leet	athh-leet
cavalry	kal-ver-ee	ka-vool-ree
dilate	die-u-laet	die-laet
escape	ek-skaep	e-skaep
et cetera	eks-set-ru	et-set-er-u
February	feb-yue-wair-ee	feb-rue-air-ee
figure	fi-ger	fig-yer
foliage	foil-ij	foe-lee-ij
height	hiet-thh	hiet
jewelry	jue-ler-ee	juel-ree
liable	lie-bool	lie-yu-bool
library	lie-bair-ee	lie-brair-ee
nuclear	nue-kyue-ler	nue-klee-yer
ordnance	or-di-nints	ord-nints
picture	picher	pik-cher
prerogative	pir-aa-gu-tiv	pri-rraa-gu-tiv
prescription	per-skrrip-shin	pree-skrrip-shin
probably	praab-lee	praa-bub-lee
Realtor	reel-u-ter	reel-ter
supposedly	su-ppoez-ub-lee	su-ppoez-ed-lee

Be particularly careful when quoting someone else’s words. Nothing will get you into hot water faster than quoting incorrectly or out of context, and then finding that the source of the quotation is in the audience! Be sure to vet the quote carefully by comparing it to the primary source, or by directly speaking with the person quoted, and avoid quotations that might lead to a “he said, she said” situation. And always verify the accuracy of any quotation in a foreign language.

Example. A BBC report tells the story of an official in Wales whose email request for a translation of a road sign from English to Welsh led to a humorous situation.² The official did not speak Welsh and did not verify the validity of the received reply. As a result, the following statement was placed on the sign in Welsh: “I am not in the office at the moment. Send any work to be translated.”

Punctuation

Proper punctuation is essential in formal technical documents, and we devote much space to this topic in our companion volume Engineering Writing by Design (see page 137 for the full reference). Our position regarding presentation slides is that punctuation should be handled consistently.

Example. In the absence of explicitly stated punctuation guidelines or requirements, we believe the following lists are all acceptable:

Magnets:	Magnets	magnets:	magnets
• Physics.	– physics	► physics	physics
• Materials.	– materials	► materials	materials
• Shapes.	– shapes	► shapes	shapes
• Uses.	– uses	► uses	uses

It is clear that many other acceptable formats exist. However, contrast with these examples:

Magnets:	Magnets	magnets:	magnets
• Physics	– physics,	► physics	– physics
• materials	– Materials,	► materials	– materials
• shapes	– shapes	► Shapes	– shapes
• Uses	– uses	► uses.	Uses

Note the various distracting inconsistencies.

Through random capitalization and inconsistent punctuation, you could disorient your listeners and convince them that you lack sufficient attention to detail.

Example. Does Dmitri’s slide describing how he obtained carbon dioxide give you much confidence in the outcome of his experiments?

• the sherman johnson co inc produces the BEST SOURCE of CO2 for our EXPERIMENTS.

• We ordered 300 ML Bottles;

• http://website/sjohnson.com/order-worked today

• U can even get stuff on saturday!!!

Description versus Argumentation

We have said that technical presentation is a combination of information and persuasion. The process of informing typically entails description and argumentation. Presenters must describe ideas, objects, devices, or systems. They must also put forth logical arguments. It’s important to understand that description and argumentation are not the same thing. Something you should be clear about, before opening your mouth to speak, is

Am I trying to describe something right now, or argue in favor of (or possibly argue against) something?

Suppose, for example, you are presenting a mechanical system design. A full presentation may require both description and argumentation. However, you definitely want to be clear as to which of these you are pursuing at any given moment. You could, for instance,

1. start with a pure description of what the system is, then, after finishing the description, provide arguments for why the system should be (or had to be) that way, or

2. start with a set of standard design principles and show, through logical argument, how the system structure arises.

Either of these approaches is reasonable. It’s not reasonable to oscillate between a description of something and a loose collection of arguments regarding why it must be the way it is. That will only confuse the listener.

Example. The following passage is clearly descriptive.

In a rear-wheel drive automobile, the longitudinally-mounted engine transfers torque through the clutch to the transmission. The transmission connects to the drive shaft through a U-joint, and the drive shaft to the differential through another U-joint. The axle shafts then transfer the engine torque to the wheels through CV joints.

It tells the listener what is, not why it had to be that way. It is not argumentative. The speaker does not draw conclusions from given facts (deductive argument) or try to generalize from known facts (inductive argument). He or she concentrates, at least for the moment, on painting a picture.

Example. This passage is clearly argumentative:

The point-to-point communication link implemented in our project requires the use of a high-gain antenna. Possibilities include reflector antennas, phased arrays of patches, and Yagi-Uda dipole arrays. We have chosen to use a 10-element Yagi-Uda array because of its low cost, simplicity of construction, and insensitivity to harsh environmental conditions.

Example. Consider this snippet of a talk:

Let’s take a look at our system. The input signal goes in the front. Sometimes you have to have two outputs for high efficiency. The output signal comes out here. Sometimes the signal comes out of the other side because of high efficiency. When it doesn’t, we can’t get our high efficiency. So we have two outputs. Remember, folks, it’s all about efficiency!

Did you find this hard to follow? The passage is neither description nor logical argument, but merely an example of bad engineering discourse. Don’t do this.

Cues for Logical Argument

You can tell that logical argument is taking place by looking for these key elements

1. definitions (“Suppose we let m be the mass of the … ”)

2. logical implications (“if … then …”) and

3. logical equivalences (“… if and only if …”).

Key words to look for are premise indicators such as since, because, and in view of the fact that, and conclusion indicators such as therefore, hence, and we conclude that. Learn to recognize and use these appropriately during your presentations, so that you don’t sound like the speaker in the preceding example. For reference, let’s list some common premise and conclusion indicators in English.

premise	conclusion
since, because	therefore, hence, thus
in view of the fact that	we conclude that
by virtue of	it follows that
for	consequently
inasmuch as	we may infer that
as indicated by	which implies that

Again, these should only appear in argumentation.

Some Pointers on Description

If you want to deliver a clear and informative description, pay close attention to the following classical recommendations.

(a) Keep your standpoint clear.

This is particularly important in engineering. Was your photograph of the construction site taken looking to the east, or to the west? Does it view upslope, or downslope? Was it taken in the spring during a period of temporary flooding, or during late summer so that the standing water is permanent? Each piece of information could be crucial to the audience’s understanding of your explanation. If you switch between views as you scroll through your slides, be sure to keep the audience oriented. Make your descriptive standpoint clear.

Example A. Moira is describing her new technique for reducing corrosion inside electrical motor housings.

On this slide you see five figures. At the center is a photograph of the interior of the motor housing, with a position marked with a red X. At the top are two micrographs made from samples at this position. On the left is a sample that was made before the treatment started. On the right is a sample taken five weeks after treatment. For comparison, the figures at the bottom show samples from the same two times taken from an untreated portion of the housing. It is clear that the treated sample has experienced far less corrosion than the control sample.

Moira was careful to orient the audience to the physical position of the samples (inside the housing) and also to the temporal position of the measurements (five weeks apart). This gave the audience the information they needed to assess the validity of Moira’s conclusion regarding the corrosion treatment.

(b) Put great thought into selection of details.

Include what is necessary and no more.

Example. In Example A above, Moira could have said “We began the testing on August 24, and ended on September 30.” This also provides the information that the test lasted five weeks, but that number must be teased out of the dates. Unless the time of year of the tests was important, specifying the duration was sufficient.

Provide the listener with a coherent picture. If certain details are grouped naturally in your subject, they should be grouped intentionally in your presentation. Don’t jump around haphazardly.

Example B. Contrast the description of Example A with the following.

The treated sample turned out the best, as you can see. Both samples were taken after five weeks. The control sample is shown on the bottom and the treated sample is shown on top. The samples were taken from inside the housing. The left figures show before the treatment, and the right pictures show after. The control was not treated.

Confusing, yes?

Crucial details can be emphasized by placing them first or last in the description. However, be careful that sufficient background information has been provided for the audience to understand the material described. In Example B, Moira emphasized the fact that the treated sample has less corrosion by mentioning this first. However, the audience had no point of reference by which to gauge the importance of the conclusion. In Example A, Moira waits until the audience is prepared, then makes a strong concluding statement based on the information she has provided.

These considerations show how important it can be to have a plan for delivering a description. Good descriptions don’t just happen — they are deliberately and skillfully designed.

Other Aspects of English Usage

Ideally, a technical presenter will have all the grammatical skills of a good technical writer. This is not to imply that you must speak in the same formal way that you write; overly formal speech is generally unappealing, even in a technical presentation. However, this does not give you free rein to pepper your language with slang, cliches, or regional colloquialisms. You should strive to balance the level of formality needed to accurately convey your information with a genial tone that makes the audience feel comfortable.

We would make slightly different arguments about material written on your slides. Although we would not consider a slide as a formal document subject to the rules of formal grammar, we think it’s best if slides do not say blatantly ungrammatical things.

Example. Imagine seeing the following bullet point on a technical slide:

• their are too solutions to equation (1)

First you’d have to translate it as

• there are two solutions to equation (1)

Then you might be annoyed by the fact that the presenter didn’t write instead

• equation (1) has two solutions

which is shorter and more direct. But a mere confusion over English choices such as their/there/they’re and to/two/too could cast doubt on the presenter’s attention to detail.

There are simply too many of these issues to cover in a book on technical presentation. A reader interested in deepening his or her grasp of formal engineering writing could consult our companion volume Engineering Writing by Design: Creating Formal Documents of Lasting Value. Again, the full reference appears on page 137.

4.5 Mathematical Discourse

The art of communicating mathematical content is an extensive one encompassing both written and spoken phases. In this book, we assume you are an engineer preparing to address an audience composed mostly of engineers. Even so, depending on your area of specialization, your talk may be quite mathematical in nature (areas such as control theory and information theory come to mind). Or you may simply have a few equations localized on a couple of slides or sprinkled among your bullet lists, graphs, charts, diagrams, and photographs. Either way, we think it is sensible to break the issue of mathematical content down into main subissues: the equations on your slides, and what you plan to say about them.

The Equations Themselves

Appropriate Use of Notation

Let’s start with the obvious: an equation must contain an equals sign. The following are expressions, not equations:

V2/R,me42ℏ3n2[1−(nn + 1)2],∫0∞f(t)e−stdt. $\begin{matrix} V^{2} / R, & \frac{m e^{4}}{2 ℏ^{3} n^{2}} [1 - {(\frac{n}{n + 1})}^{2}], & \int_{0}^{\infty} f (t) e^{- s t} d t . \end{matrix}$

The one on the far right, for example, could be used to write an equation defining the Laplace transform of a function f(t):

F(s) = ∫0∞f(t)e−stdt. $F (s) = \int_{0}^{\infty} f (t) e^{- s t} d t .$

But all by itself it is not an equation. One should never be overtly sloppy with mathematical symbols or terminology.

Example. Here are some examples of mathematical carelessness from student slides:

Ms = 4πMsf=∑n=1N[n2 + 2n3F → maw = ∑n=Nxn∫cos x = sin xf(θ) = cos(theta) $\begin{array}{l} M_{s} = 4 π M_{s} & w = \sum_{n =}^{N} x_{n} \\ f = \sum_{n = 1}^{N} [n^{2} + 2 n^{3} & \int \cos x = \sin x \\ F \to m a & f (θ) = \cos (t h e t a) \end{array}$

Because a talk is less formal than a formal document, however, some additional latitude does exist. In a formal written document, we would insist that the equals sign be kept out of non-formula text. Even on a slide, we would never condone

Concrete is strong and = the best option

But, as clarity and efficiency are the main requirements for text on slides, we would assent to a sensible and consistent use such as

t = time variable

s = Laplace transform variable

f = given signal

F = Laplace transform of f

While slides are not necessarily about formality, they are still about effective communication.

How Many Equations?

Our answer is “not too many, but possibly more than you will actually refer to in the talk.” The density of equations on your slides depends on a number of factors.

Example. Anita is talking to the local chamber of commerce about health effects from the fields produced by cell phone towers. Although she wishes to discuss topics like Specific Absorption Rate, which could easily be explained to engineers using a few equations, she knows her audience is not well-versed in mathematics and decides not to include any equations at all.

Example. Jose recently graduated with his Ph.D. in mechanical engineering and is preparing a short presentation that he will give to a group of staff scientists and engineers during a job interview. His goal is to convince the audience of his technical prowess rather than to educate them on the subject of his graduate thesis, so he chooses to include far more equations than he can cover, and plans to highlight the main ideas that they support. Being skimpy with technical detail could cause the selection committee to question the depth of Jose’s knowledge on his thesis topic.

Most often some choice in between these extremes is best. At a technical conference, for instance, you might include several equations that are immediately recognizable by the audience, and require little description, but are needed as a lead-in to the novel contributions of your work or to define various terms.

What You Plan to Say about Your Equations

One of the hallmarks of seasoned technical speakers is their handling of equations during a presentation. Here are a few pointers to avoid coming across as an amateur. Considering them now could help you in the initial build stage of your presentation.

1. Don’t read your equations symbol by symbol. The audience can see what the equation says; you should be telling them what it means.

Example. While displaying an equation such as

Uave=14π∫∫ΩU(θ, ϕ) dΩ $U_{ave} = \frac{1}{4 π} \int \int_{Ω} U (θ, ϕ) d Ω$

you could simply say:

The average radiation intensity is given by this expression.

You might even add

Recall that the integrand function is the radiation intensity along a specific direction.

But don’t point to each symbol and say:

U sub ave equals one over four pi times the double integral over omega of U of theta and phi d omega

without an especially good reason.

2. Don’t believe you must refer to every equation you display. Your equations shouldn’t control your presentation — you should. There are various reasons for glossing over an equation during a presentation. Maybe your audience is intimately familiar with the equation and no explanation is needed. Or maybe you are running short on time. Or perhaps you included the equation as insurance against confusion, but recognize that extra clarification is not needed.

3. Try to encapsulate the essential meaning of an equation. Is the equation challenging to solve, or is it relatively routine? Does it show that a quantity of importance is large or small? Does it show that something is increasing or decreasing? Does it show that a process is optimal, or that a system is stable? An equation can take a large effort for a listener to digest. Why should he or she care about this particular one?

4. Be logical. If certain equations lead to other ones, and if that’s important, then say so. Don’t confuse the audience by skipping around so that the connection between mathematical ideas becomes obscure.

5. Don’t forget the English part. Certain words must be used to explain mathematics properly in English: substitute, simplify, solve, recast, manipulate, invert, differentiate, integrate, and so on. Terms such as these are seldom synonymous: simplify does not mean the same thing as substitute, for instance.

Example. Consider substituting the value x = 3 into the equation f(x) = x cos(x). Don’t say:

I solved f(x) for x = 3.

Instead, say:

I evaluated the function f at x = 3.

The words solve and evaluate have different meanings.

4.6 Visual Aids

Here we consider the things you’ll bring along to help you communicate with the audience. These may include slides, videos, equipment demos, etc.

Slides

As visual aids, slides can serve a number of purposes:

1. Provide a means to organize the talk. It might be difficult for a speaker who is not well trained or experienced to work without organizational aids.

2. Provide transitional aids and visual cues about content, for both the speaker and the audience. You don’t want to forget anything important, so write it down!

3. Efficiently display specific technical information — graphs, charts, diagrams — for the purpose of information transfer to the audience.

4. Provide the audience something to engage with. This is helpful for speakers who have difficulty establishing rapport with an audience.

5. Provide an archive of the material presented. Often the slides constitute the only record of the talk (be it a briefing, pitch, interview talk, or a conference presentation that does not have an associated proceedings document). This is a good reason to put care into your choice of material for inclusion on your slides.

What Should My Slides Look Like?

The overall feel of a presentation is largely determined by the look of the slides. This is where you can lend a personal touch to your presentation, but you may be bound by certain restrictions. For instance, your company or the conference organizers may specify a required template. If you have complete freedom, you may want to start out using one of the many sample templates provided by commercial presentation software packages, or find something you like on the web and duplicate it. We list below several considerations for what to include.

We suggest you follow the old adage and keep it simple, but also keep it clean and uncluttered. An example slide created by the authors in Microsoft PowerPoint^® is shown in Figure 4.4, and took just a few minutes to make. We use black, white, and gray for our examples, but you will certainly want to use a color background with perhaps a watermark, gradient, or some pleasing pattern (more about color below).

How Many Slides?

There is no magic rule regarding the number of slides to prepare. You are carrying out a design process and must consider what would be best for your purposes. Remember that your main goal is to communicate a certain amount of information to your target audience.

Even a presentation without slides is possible.³ Slides are visual aids; this implies they are used — if at all — to help the speaker connect with the listener. You needn’t make slides for the sake of slides, or 20 slides for the sake of 20 slides. You especially don’t want to find yourself racing through slides just to “get through” everything you brought along. Nor do you want the slides to take over the presentation (or provide an ineffective “crutch” by giving you the opportunity to read them verbatim). So prepare what seems like a reasonable number of slides for the main part of your talk. The rehearsal phase (Section 5.1) will give you a chance to adjust your slides (both in number and in content).

FIGURE 4.4

A simple PowerPoint^® slide template created for this book.

Also keep in mind that it may be wise to design some auxiliary slides for use during the question-and-answer part of your talk. You may never use these, but it’s better to be safe than sorry.

Example. Busy managers encourage their engineers to keep the number of slides in their presentations small, both to minimize the time spent in scheduled briefings and to lessen the burden of reviewing the slides. Recall that presentation slides often represent the only physical record of a briefing or idea pitch, and should be prepared carefully with knowledge of their archival value. Many organizations are stressing the use of just a few information-intense slides, with many visuals (graphs, pictures, flowcharts) and few words. Some groups employ a single briefing slide, usually broken into four panels, often called a quad chart.

Using just a few sparsely worded slides puts the burden on the speaker to know his material well. JoAnne adopted a strategy to help with her monthly briefings. She first created a presentation with many words and visual cues. These helped organize her thoughts and make sure she omitted nothing important. After rehearsing the presentation several times to herself, she cut the number of slides by half, keeping most of the visual information but eliminating slides that contained mostly words. She rehearsed again, eventually paring the number of slides to four. She checked that all essential information was still present on the slides so that someone reviewing them later could retrieve the underlying points and any important supporting data. JoAnne’s boss and her colleagues appreciated her new presentation style. Her briefings seemed more spontaneous; no longer fixated on following the word structure of her slides, she was better at engaging her audience.

The Content of a Slide

As a component of your designed presentation, a particular slide should have a definite purpose. It may contain text, equations, a table, a chart, a graph, a diagram, a photograph, or a combination of these elements. There are few universally applicable rules about the content of a slide. A classic one is not to crowd any given slide with too much material. It is safe to say that an audience should never be required to read anything over a few words in length. Long figure captions, long paragraphs, etc., should be avoided.

Example. Alexander’s biggest worry about his upcoming presentation was that he might forget to say something important. So he filled his slides with everything that might be needed. His plan was to formulate his points during rehearsal and adjust on the fly according to audience reactions. Unfortunately, slides crammed with material led to overconfidence and Alexander didn’t prepare as well as he should have. When the big day came he resorted to reading directly from the slides. The listeners felt overwhelmed by the long paragraphs of tiny text, and Alexander’s monotonous recitation quickly caused them to disengage.

Alexander’s slide might have looked like Figure 4.5. The audience is left to wonder whether they should be reading everything they see, and the speaker is tempted to recite verbatim. A better alternative is shown in Figure 4.6. Only the main points are included, which Alexander can use as cues and the audience can use as a helpful guide. Of course this requires significant rehearsal, so that each point may be elaborated on as appropriate.

There is a difference between a slide with a lot of content and one with “too much text.” Recall JoAnne’s experience showing that a lengthy and detailed presentation can be made from a single slide with dense content. Space on presentation slides is a form of real estate worthy of much consideration, and there are few hard and fast rules. Use this as a guide, however: never include the trivial or the obvious.

Example. Jeremy displayed a picture of a three-terminal electrical device during his presentation. The very simple diagram was labeled “three-terminal electrical device.” The listeners, all electrical engineers, felt insulted. Yes, they knew he was speaking about electrical devices. And yes, they knew how to count to three!

Slide Layout

This is where either a natural eye or an awareness of some graphic design fundamentals can be helpful. The latter subject covers issues of visual unity, balance, contrast, proportion, color, etc., and we recommend a few books in Further Reading on page 135. The pointers below are merely the results of our informal observations of slides made by engineers.

1. Again, don’t crowd a slide with too much material. Graphic designers talk about white space and why it’s important to have some. Do whatever you can keep your slide clean and clutter-free. A slide should contain a workable amount of information. If the presentation must be done on one slide with four panels, you will have to work extra hard to keep it readable.

2. Choose a legible font. The world of electronic fonts is constantly changing, so it is impossible to give a fixed recommendation about font choice. But you should certainly avoid exotic or cutesy fonts. And be sure your fonts are large enough to be deciphered from the back row of seats.

3. Make careful decisions about the use of color. Color can certainly add much interest to your slides. But in a formal technical presentation, color should be kept under control. Don’t run wild with color for its own sake. Ideally, color should be there to communicate something of value (red for hot or warning, for instance). And remember that certain color combinations are garish, unappealing, or just plain difficult to see (such as yellow text on a white background). Also, keep in mind that a non-negligible fraction of your audience may be fully or partially color blind. This is a good reason to use color as an information enhancer rather than an information carrier.

FIGURE 4.5

Too much text for one slide!

FIGURE 4.6

A clean slide containing the main ideas as cues for the speaker.

4. Try to group related elements. If an equation and a figure are related, perhaps they could appear on the same slide (as long as the slide is not crowded as a result).

5. Understand that a slide may look different on a projection screen than it does on your computer screen. All your layout decisions should be regarded as provisional, subject to change after the rehearsal phase.

6. Consider the use of templates. Many commercial software packages, such as Microsoft PowerPoint^®, have standard templates to help you lay out the various elements of your slides. Many other templates are available on the web. Your organization may have specific templates, either required or suggested. Conferences often have a required format or uniform template.

7. Consider the use of graphical tags. Small graphical elements may be added to each slide to identify your organization, the conference you are speaking at, or the project you are working on. These are usually placed at the corners, tops, or bottoms of the slides.

8. Include informative titles. Titles quickly convey to the audience the content of the slide. Use a large font and consider separating the title from the rest of the slide with a line, box, or other graphical element.

9. Don’t forget the possibility of footers. The footer space at the bottom of the slide can be used for a variety of purposes. Consider including the slide number (for audience reference), the date, your name, the name of the speaking venue, or other significant information. This is useful if individual slides are extracted later from an archive of your presentation.

10. Be cautious with backgrounds. Presentation software generally allows you to select a background image, pattern, fixed color, or color gradient. These may enhance the look of the presentation if used subtly. Avoid garish backgrounds or backgrounds that hide or distract from your slide material. When using an image or watermark, be sure it is faded sufficiently to be discreet.

11. Don’t go wild with animation and sound. Subtle animation, such as a text box opening up, can help to engage the audience. However, objects that fluctuate, spin, dance, vibrate, explode, or do many of the other visual tricks provided by presentation packages can be annoying. Remember that you are giving a professional presentation. Similarly, avoid cartoon-like sound effects. An exception is a movie or other animated element used to convey information.

12. Be careful about actively linking to web pages. Web pages are notoriously transitory. If you plan to click on a web link during your presentation, be sure the page still exists before starting the talk.

Example. Tammy was a member of the internet generation. Her earliest reading experiences were associated with colorful web pages, pop-up advertisements, and flashy videos. So, she naturally assumed a good technical presentation must be equally splashy, with much color, animation, different fonts, varying text position and size, and lots of graphical elements. What she eventually learned is everything in moderation. A little flash and an occasional splash of color catches the audience’s eye, but too much is just plain distracting. It is the speaker’s job to keep the audience’s attention through an engaging speaking style and by emphasizing the interesting nature of the material.

If you were in the audience and saw the slide in Figure 4.7, how would you react? In contrast, consider how Shreya’s engineering eye quickly figured out a better approach.

Example. As an undergraduate researcher, Shreya had watched many graduate students give presentations to her research group. Now that she had graduated and been accepted as a masters student, she was expected to similarly brief the group on her work. She had taken many notes during the past year on how students presented, the content of their slides, and the reactions of the group members — particularly her faculty adviser. She saw that the group was most receptive when the speaker concentrated on just one or two main points, including background information and recent accomplishments. She constructed several clean slides, each with just a few bullet points, an illustrative graphic showing the machine she was studying, and a plot or table summarizing recent results. She provided additional relevant information orally, emphasizing the important points with energy and enthusiasm. Her careful notetaking paid off; she was praised by her group mates and her adviser for a coherent and informative report.

Clear Equations

Among the most technical elements that appear on slides, and the hardest for audience members to digest, are mathematical equations. The utmost care should therefore be taken to produce logical and visual clarity. Positive examples of equation layout can be seen in practically any engineering textbook (but not necessarily on web pages). In addition to such obvious issues as font size, pay close attention to how multi-line equation displays are treated. Notice, first, that an effort is made to align equality signs vertically.

FIGURE 4.7

This slide is a mess!

Example. This is a nice multi-line equation display:

y(t)=∫∞−∞h(λ)x(t−λ)dλ=∫∞−∞Ae−λ/τ U(λ)B U(t−λ) dλ=AB∫t0e−λ/τ dλ=AB τ(1 − e−t/τ). $\begin{array}{l} y (t) & = \int_{- \infty}^{\infty} h (λ) x (t - λ) d λ \\ = \int_{- \infty}^{\infty} A e^{- λ / τ} U (λ) B U (t - λ) d λ \\ = A B \int_{0}^{t} e^{- λ / τ} d λ \\ = A B τ (1 - e^{- t / τ}) . \end{array}$

Note the vertical alignment of the equality signs.

Then, if an expression must be broken because of excess length, the break occurs at a sensible spot.

Example.

Pe===12∫VT−∞12π−−√σ0exp[(−r0−s01)22σ20]dr0+12∫∞VT12π−−√σ0exp[(−r0−s02)22σ20]dr012∫∞(−VT−s01)/σ012π−−√exp(−λ22)dλ+12∫∞(VT−s02)/σ012π−−√exp(−λ22)dλ12Q(−VT+s01σ0)+12Q(VT−s02σ0). $\begin{array}{l} P_{e} & = & \frac{1}{2} \int_{- \infty}^{V_{T}} \frac{1}{\sqrt{2 π} σ_{0}} \exp [\frac{{(- r_{0} - s_{01})}^{2}}{2 σ_{0}^{2}}] d r_{0} \\ + \frac{1}{2} \int_{V_{T}}^{\infty} \frac{1}{\sqrt{2 π} σ_{0}} \exp [\frac{{(- r_{0} - s_{02})}^{2}}{2 σ_{0}^{2}}] d r_{0} \\ = & \frac{1}{2} \int_{(- V_{T} - s_{01}) / σ_{0}}^{\infty} \frac{1}{\sqrt{2 π}} \exp (\frac{- λ^{2}}{2}) d λ \\ + \frac{1}{2} \int_{(V_{T} - s_{02}) / σ_{0}}^{\infty} \frac{1}{\sqrt{2 π}} \exp (\frac{- λ^{2}}{2}) d λ \\ = & \frac{1}{2} Q (\frac{- V_{T} + s_{01}}{σ_{0}}) + \frac{1}{2} Q (\frac{V_{T} - s_{02}}{σ_{0}}) . \end{array}$

Sensitivity with respect to details like these is what leads to an overall workmanlike effect. Your equations will be easier to present and easier for the audience to grasp.

As with text, there is a temptation to read equations verbatim. If the speaker is not a diligent rehearser, he may resort to saying

“… we use the curl of E equal to minus d B d t equation in the next equation of the integral from a to b of E dot d L … ”

Instead, the speaker should provide context for the equation:

“… substituting Faraday’s law into the expression for voltage allows us to …”

If the speaker emphasizes the meaning and importance of the equations, it is possible to include quite a few on a slide — as long as the audience is not overwhelmed by the sheer density of mathematical symbols. Figure 4.8 shows a slide used by one of the authors at a technical conference. While the slide seems to contain a large number of equations, the author emphasized their relevance to the problem being analyzed. He did not dwell on the particular mathematical form of each equation. He also assumed the audience had a basic familiarity with the symbols and an understanding of their meaning, and included a graphical element to identify geometrical parameters. Mathematical rigor is always important; there is value in mathematical detail when the presentation is archived for later reference.

Readable Diagrams and Graphs

Engineers often convey information through diagrams, graphs, and tables. The key difference between using these items in a presentation versus a written document is the time the user has available to glean information. A reader is able to dwell over a complex diagram for as long as it takes to extract the needed information. During a presentation, he may have only one minute to do the same. This may be impossible, even under the guidance of the speaker.

Key on these two things: readability and complexity. An audience member must be able to see and understand the graphic element from the far end of the room (just as she must be able to hear your words). Readability means that the shapes must be clear, the fonts large, and the lines bold. Complexity implies that you should not overwhelm the listener with content. How will he react to a diagram with a hundred elements? Probably by tuning out.

Both diagrams and graphs must follow the same rules of readability and complexity, so let’s concentrate on graphs. A bad graph might have any of these characteristics:

1. Fonts too small (readability). Can your text be seen from the back of the room?

2. Color used poorly (readability). Be careful when combining colors. Contrast is essential. Do not, for instance, put a yellow line against a white background.

3. Lines too thin or not differentiable (readability). Thin lines are hard to see. Data lines must be distinguishable in some way. Use different line types, but never so many that you cannot tell them apart.

4. Background too busy (readability). Data lines are difficult to see when placed against a patterned background.

5. Too many graphs on a page (readability and complexity). You may want to put several graphs on a page so that you can contrast and compare results. This can be done, but only with great care. Small graphs must be balanced by fonts that appear unusually large and by lines that appear unusually thick. Unless kept particularly simple, multiple graphs on a slide can quickly overwhelm the audience.

FIGURE 4.8

A slide with a lot of mathematical detail. Don’t read the equations verbatim!

6. Captions too long (complexity). Don’t include too much information in a caption. The audience may feel compelled to try to read the entire thing, which will distract from your message. Consider placing essential supporting information in a separate text box or in a table, either within or outside the area occupied by the graph.

7. Legends complicated or ambiguous (complexity). You may opt for a legend if you have several data lines on a graph. This can distract an audience member, who will have to correlate the line types, symbol types, or colors with the legend. If there are several lines, it may be hard to discriminate between them. Instead, include annotations next to the lines. This gives immediate contextual meaning.

Figure 4.9 shows a graph with many of these issues. Imagine viewing this slide from the back of the room! Contrast this with Figure 4.10. Considerations of readability and complexity provide visual benefits that are quickly apparent.

Should I Include Tables?

It is rarely beneficial to tabulate long lists of data. This type of data is best presented using a graph. However, smaller tables are fine as long as readability and complexity are adequately addressed. Compare Tables I and II in Figure 4.11. The data in Table I is overwhelming and hard to assimilate. This information could easily be plotted in a graph and thereby made accessible. In contrast, the data shown in Table II does not lend itself to graphical representation and is best tabulated. It could be quickly explained and contrasted without trying the listener’s patience.

Demo Equipment

Although slide presentations seem to be the norm for engineers, there are times when only a live demonstration will do. Here are some pointers we’ve gained from experience.

1. Make sure the entire audience can see the demo. This may be easily accomplished if you are demonstrating the function of a new car window. But how are you going to demo a hand-held blood pressure monitor in an auditorium?

If the audience is large, consider using one or more cameras and a monitor or projection screen. The camera can be focused on a device, output display, input panel, or some visual aid. If you lack access to a camera, consider using a prerecorded video of the demo to show the larger audience while presenting the demo live to a smaller audience (of judges, for example). Cameras can also be used to record the demo or stream it to the web.

FIGURE 4.9

A bad graph.

FIGURE 4.10

A good graph.

FIGURE 4.11

Using tables in slides.

2. Audience safety is paramount. The authors have witnessed capstone design presentations involving projectiles, whirling saw blades, noxious gases, sparking electrodes, laser emissions, and so forth. Your listeners should not have to worry about their personal safety while attending your talk.

3. If possible, have a backup unit with you. Remember Murphy’s law and its various corollaries. Bring extra batteries if the unit is battery powered.

Example. Marshall was thrilled when the device he invented won the student design competition sponsored by his professional society. The best part was that he got to attend a European conference where he would demonstrate his prize-winning contraption. Trying to set his project up at the conference center, Marshall found that the wall outlets differed from those in the USA. He wasn’t too worried, since his demonstration wasn’t until later that day, and asked around until he found someone with an adapter plug. He connected everything to his satisfaction, flipped the switch, and pow — his power supply belched smoke and died a horrible death. Only then did he learn that Europe uses 220 volts, while he had designed his power supply for 110 volts. Unable to fix his contraption, Marshall was forced to talk about how it would work if it had electricity. A little homework would have saved much embarrassment.

Posters

Poster presentations are now common at conferences and review meetings. The speaker is usually expected to stand beside a large visual aid (a poster) and interact one-on-one with interested viewers. Here are some things to keep in mind while preparing your poster and giving your presentation.

1. Be aware of formatting requirements. The allowable poster size is determined by the table or easel on which the poster is mounted. The authors have seen beautifully prepared posters drooping ingloriously because they were too large for their supports. There may also be specific requirements about the title size, the fonts, the organization of the material, or the number of panels. Some conferences dissuade presenters from using multiple sheets of paper. Others even permit multiple easels.

2. Control the amount of content. Authors may be tempted to compress an entire oral presentation onto a poster. This generally leads to a cluttered, visually unappealing, confusing mess. Omit any details you can provide to an interested viewer during discussion, and concentrate on main ideas.

3. Spatial layout is important. Posters differ from oral presentations because all aspects of the presentation are available to the viewer at once. This can be overwhelming unless some spatial structure is present. One approach is to replace the temporal sequence of slides in an oral presentation by a spatial sequence of ideas. Use clearly delineated panels with titles to guide viewers through the sequence. Another approach is to organize the poster around carefully placed graphical elements. This is appropriate if the order of information access is not important.

4. Be conscious of visual aspects. Many of the same concerns regarding slides are appropriate here. Format graphs and equations properly. Avoid lengthy captions and large tables. Be careful with color and font selection. Be sure that everything is easily readable by someone standing several feet from the poster (don’t annoy the viewer by requiring her to stoop over and squint at microscopically small fonts).

5. Know the rules. You may be required to install your poster at a certain time and remove it before the next poster session. There may be a specified time period during which you are required to attend your poster to answer viewer questions. Be sure to wear the attire expected of oral presenters.

6. Consider ancillary elements. It might be helpful to bring electronic copies of your poster to distribute to interested viewers. You might also wish to distribute a business card or photograph of your product, system, or experiment. Consider bringing a demo unit or other physical items if allowed.

4.7 Ethics

To what extent must a speaker be concerned with ethics? Isn’t it true that, unlike the written word, the spoken word has only temporary effects? Don’t you believe it!

Example. Jim took liberties and made a false statement to get a questioner off his back. Jim wasn’t aware that others in the audience were recording his talk on their smartphones.

In fact, speaking is just as serious as writing. All of professional communication is serious; practically by definition, professionals have access to specialist knowledge that the general public does not have. This places significant responsibility on you as an engineer. Any false statement can terribly mislead and do real damage (to yourself and others). One of the best things a presenter can do is to continuously monitor whether he or she is speaking in an ethical fashion. Consider this dimension while building your materials; it’s a necessary part of vetting them for readiness.

Like logic, grammar, mathematics, and graphic design, the subject of ethics can easily fill a whole book (we list a few on page 138). Fortunately, the various engineering professional societies and organizations have done a reasonably good job of distilling classical wisdom into their official codes of ethics. Although an ability to recite the code published by your own organization would be ideal, even a passing familiarity with the ethical code published by any of the major engineering societies would provide you with some valuable insurance as a technical speaker. The codes published by the Institute of Electrical and Electronics Engineers (IEEE) and the American Society of Mechanical Engineers (ASME) represent excellent starting points for consideration. The IEEE Code of Ethics, for example, contains provisions against conflict of interest, bribery, falsifying data, and taking credit for the work of others. The very act of joining the IEEE means that you agree to these provisions.

It should go without saying that there are frequent and significant intersections between ethical codes and the laws of various countries. People who have been granted security clearances must be extremely cautious with their written and spoken communications. But engineering ethics takes on many forms, depending on the type of work involved. In the US research community, engineers are bound to act responsibly as described in, for example, the National Science Foundation’s policy of Responsible Conduct of Research.⁴

Example. Shannon is a Ph.D. student watching her adviser give a presentation at a small local conference. He is describing recent experiments that Shannon conducted in their research laboratory. She notices that he is only describing the experiments that produced results which validate their working theory, and that several experiments that returned negative results are being overlooked. After the conference she confronts him and tells him of her discomfort over his “cherry picking” of results. He tells her not to worry — these are preliminary results and a better experiment will return improved data before they publish in the open literature. “Besides,” he says, “this is a small conference and there is nobody really important here. And no one will remember what we showed anyway.”

4.8 Checklist: Building Your Presentation

□ I have established the target specifications for my talk

□ I have established the scope of my talk

□ I know what topics I want to cover

□ I have thoroughly investigated the motivations and interests of the audience

□ I understand the time limitations

□ I understand the venue limitations

□ I have prepared my visual aids

□ I have selected appropriate presentation software

□ I know whether specific software must be used

□ I am familiar with the software or willing to learn

□ I have created a slide template

□ I know whether a format is required

□ My template includes helpful information

□ Title

□ Page number

□ Graphical tag (e.g., organizational logo)

□ Footer or header with date/venue/presenter etc.

□ My template is clean and uncluttered

□ I have decided on the number of slides to use, based on time limit and audience needs

□ I have checked the appearance of all my slides

□ Fonts are appropriate

□ I did not mix too many fonts

□ The size is sufficient to see from all points in the venue

□ The amount of material on each slide is appropriate

□ The number of equations, tables, and figures on each slide is appropriate

□ I did not combine too many elements

□ I did not use too much text

□ There is not more text than the audience can easily read

□ I only include enough text to provide myself cues and give the audience a point of focus

□ Color is appropriate

□ I chose color carefully

□ I did not mix too many colors

□ Color combinations are distinctive

□ I considered the impact of color on audience members who are color blind

□ Slide background is appropriate

□ The background is not too dark

□ The background is not too busy

□ The background is not distracting

□ Adjunct elements are appropriate

□ Animation is not overbearing or otherwise distracting

□ Sound or movies add to the impact of the presentation and are not just for show

□ Active links to web pages do not disrupt the flow of the presentation

□ My equations, graphs, and tables are easy to read

□ Font size is not too small

□ Lines are not too thin

□ Captions are short, easy to read, and meaningful

□ Legends are clear and easy to understand

□ There are not too many elements on any slide

□ I have checked the appearance of my presentation using the venue equipment or similar equipment

□ The presentation is visually appealing

□ All fonts, equations, and graphs appear as expected

□ All adjunct elements (animation, links to web pages, sound, movies) behave as expected

□ I have carefully examined my materials for any logical blunders

□ There are no fallacies of formal logic

□ There are no fallacies of informal logic

□ I have checked my materials for errors in technical claims

□ My claims are reasonable

□ My claims pass dimensional and order-of-magnitude checks

□ My claims agree with known special cases

□ My claims are in accord with known standard principles

□ My evidence comes from reliable sources

□ I have examined relevant counterexamples to my claims

□ I have checked my materials for proper English usage

□ My word choice is appropriate

□ Words have the proper technical meaning

□ Words are at the proper level of formality

□ The punctuation and spelling obey standard rules

□ My wording takes the form of either description or argumentation, as appropriate

□ My descriptive content has a clear standpoint

□ My descriptive content has the appropriate level of detail (no more, no less)

□ My descriptive content forms a coherent picture

□ I have checked my materials for proper mathematical discourse and clarity of presentation

□ I have used proper mathematical notation

□ I have not overburdened the listener with too many equations

□ My equations form a logical progression

□ I understand what I want to say about each equation

□ I have carefully planned my demo

□ The demo is easily seen by all audience members

□ There are no safety issues

□ I have a backup plan in case of loss or damage of the demo equipment

□ I have considered the special needs of a poster presentation

□ I am aware of the formatting requirements

□ I know the rules of presentation

□ I have determined the amount of material I can place on the poster

□ I have created a workable layout

□ I have replaced the temporal orientation of an oral presentation with an appropriate spatial orientation

□ I have created an alternative layout that is clear and easily understood by the viewer

□ I have created or gathered needed ancillary items (handouts, business cards, brochures, etc.)

□ I have considered any ethical implications of my presentation

□ I understand what is appropriate ethical conduct within my discipline/profession

□ I have consulted the ethical codes for my organization

□ I understand the special needs of my audience

4.9 Chapter Recap

1. The target specifications for designing your talk must consider the nature and scope of the subject material, the nature and size of the audience, the time alloted, and the characteristics of the venue.

2. Logic, grammar, mathematics, graphic design, and ethics are all key aspects of quality control when it comes to a technical presentation.

3. Learning about fallacious arguments is one effective way to avoid making them.

4. Simple set diagrams can be helpful in spotting formal logical fallacies.

5. It only takes one counterexample to invalidate a formal syllogism.

6. Know all the terms on your slides (what they mean and how to pronounce them!).

7. Be consistent with English punctuation.

8. Don’t confound the listener with a muddle. Deliver well-planned descriptions and logically sound arguments.

9. Time spent learning English grammar is valuable even for speakers who do not plan to implement every rule they encounter.

10. Mathematics is about clarity and precision. It is rarely the place for abuse of symbols or terminology.

11. Don’t plan to read your equations symbol by symbol. In fact, you can show certain equations on your slides without referring to them at all. For the most part, however, you should provide engineering-level meaning to your equations.

12. Design your slides carefully. They should be clear and inviting visual aids. There is no definite rule regarding the number of slides you should prepare.

13. Special considerations are required for a safe and successful equipment demo.

14. Be aware of the formatting and presentation requirements specific to poster presentations.

15. Engineers are professionals and are subject to ethical requirements.

4.10 Exercises

4.1. Identify the argument as valid or fallacious.

(a) Gold has a density of 19,300 kg/m³. This material has a density of 19,300 kg/m³. Therefore, this material is gold.

(b) All elements with an atomic number of 79 are gold. This element has an atomic number of 79. Therefore, this element is gold.

(d) Nobel prizes are made from gold. Some engineers have Nobel prizes. Therefore, some engineers have gold.

4.2. Assume P, Q, R, S are statements. Are the following argument forms valid? Explain.

(a) P or Q.

If P, then R.

If Q, then R.

Therefore, R.

(b) P or Q.

If P, then R.

If Q, then S.

Therefore, R or S.

If P, then R.

If P, then S.

Therefore, not-P.

(d) Not-R or not-S.

If P, then R.

If Q, then S.

Therefore, not-P or not-Q.

4.3. Consider the following list of invalid categorical syllogisms. Find a real-world counterexample that reveals each syllogism as invalid.

All P is M.	All M is P.	All M is P.
Some S is M.	No M is S.	All M is S.
∴ Some S is P.	∴ A No S is P.	∴ All S is P.
No M is P.	Some P is M.	Some M is not P.
All M is S.	Some S is M.	Some S is M.
∴ No S is P.	∴ Some S is P.	∴ Some S is P.
Some M is P.	No P is M.	Some M is not P.
Some S is not M.	No S is M.	No S is M.
∴ Some S is not P.	∴ No S is P.	∴ Some S is not P.
No M is P.	No M is P.	All M is P.
All S is M.	Some S is M.	All S is M.
∴ All S is P.	∴ Some S is P.	∴ No S is P.
All M is P.	Some M is P.	All M is P.
Some S is M.	All S is M.	Some S is M.
∴ Some S is not P.	∴ All S is P.	∴ All S is P.
No M is P.	Some M is not P.	Some M is not P.
Some S is M.	All S is M.	All M is S.
∴ No S is P.	∴ No S is P.	∴ No S is P.

For example,

All P is M.	All cats have four legs.
Some S is M.	Some chairs have four legs.
∴ Some S is P.	Therefore some chairs are cats

4.4. Look for fallacies.

(a) Jones’s results are questionable because she made significant errors in the past.

(b) Since it is impossible to conceive of anything but overheating causing this problem, the problem must be due to overheating.

(c) Having discovered failures in two of the connectors tested at random, we concluded that all 5000 connectors likely failed.

(d) The vibration level increased after we heard the noise, hence the noise must have caused the vibration increase.

(e) Transistor leads are like tiny legs. Since insects have six legs, transistors have six leads.

(f) Only two possibilities exist: either the flux decreased or it increased. Since both of these represent changes, we do know that the flux changed over time.

(g) This motor is superior to the other alternatives because it is better.

(h) Resistors often have white stripes. Therefore, they seldom have green stripes.

(i) All machines are somewhat inefficient. Zach is somewhat inefficient. Hence Zach is a machine.

(j) A capacitor is an electrical device. A transistor is an electrical device. So a capacitor is a transistor.

(k) There must be something wrong with subsystem Q. Ever since it was installed, subsystem R has been unreliable.

4.5. As humans, we have cognitive biases that lead us to distort our experiences and process information selectively. Do some background reading about cognitive biases. Could any of these patterns make it easier to commit fallacies?

4.6. Consult a logic textbook (e.g., one of the books listed on page 137) to learn the Venn diagram method for validating syllogisms. Use the method to validate the following 19 syllogisms:

All M is P.	No M is P.	All M is P.
All S is M.	All S is M.	Some S is M.
∴ All S is P.	∴ No S is P.	∴ Some S is P.
No M is P.	No P is M.	All P is M.
Some S is M.	All S is M.	No S is M.
∴ Some S is not P.	∴ No S is P.	∴ No S is P.
No P is M.	All P is M.	All P is M.
Some S is M.	Some S is not M.	No M is S.
∴ Some S is not P.	∴ Some S is not P.	∴ No S is P.
Some M is P.	All M is P.	Some P is M.
All M is S.	Some M is S.	All M is S.
∴ Some S is P.	∴ Some S is P.	∴ Some S is P.
Some M is not P.	No M is P.	No P is M.
All M is S.	Some M is S.	Some M is S.
∴ Some S is not P.	∴ Some S is not P.	∴ Some S is not P.
All M is P.	No M is P.	No P is M.
All M is S.	All M is S.	All M is S.
∴ Some S is P.	∴ Some S is not P.	∴ Some S is not P.
	All P is M.
	All M is S.
	∴ Some S is P.

Note that care is required with the last four of these in cases where empty sets are permitted. The syllogisms in the sixth row only hold if the class M has at least one element. The last entry only holds if P has at least one element.

4.7. Check the following equations for dimensional correctness.

(a) The kinematic relation x = x0 + v0t + 12at2 $x = x_{0} + v_{0} t + \frac{1}{2} a t^{2}$ , where x and x₀ are distances, v₀ is a speed, a is an acceleration, and t is time.

(b) The kinematic relation v2 = v20 + 2a(x−x0) $v^{2} = v_{0}^{2} + 2 a (x - x_{0})$ , where the quantities are as in part (b).

(c) The kinematic relation v = (2gh)^1/2, where v is a speed, g is the free-fall acceleration constant, and h is a height.

(d) The energy balance relation 12kx2 = 12mv2 $\frac{1}{2} k x^{2} = \frac{1}{2} m v^{2}$ , where k is a spring constant, x is a displacement, m is a mass, and v is a speed.

(e) The rotational kinematic relation θ = ω0t + 12αt2 $θ = ω_{0} t + \frac{1}{2} α t^{2}$ , where θ is an angle in radians, ω₀ is an angular speed, α is an angular acceleration, and t is time.

(f) Bernoulli’s equation v²/2 + gz + p/ρ = constant, where v is a speed, g is the free-fall acceleration constant, z is a height, p is a pressure, and ρ is a density.

4.8. Some groups of words are easily confused because, for instance, they sound alike. For example

• their, there, they’re

• lead, led

• we’re, where, were

• sight, site, cite

• all together, altogether

• its, it’s

• passed, past

Make a list of words that you personally find confusing.

4.9. Engineering speakers are not the only ones embarrassed by improper word choices or by usage blunders. The Internet is rife with hilarious examples appearing in newspaper headlines and on signs. Make a list of your favorites. Take particular note of any you think you might have made yourself (if you hadn’t done this assignment first!).

4.10. Classify the following passage as description or argumentation.

Let P and S designate the primary and secondary planes, respectively, of the transformer. Our goal is to reflect the secondary circuit to the primary side In this case we may replace the circuit to the right of plane P by its Thevenin equivalent. Consider the open-circuit terminal voltage. Since I₁ = NI₂ and I₁ = 0, we have I₂ = 0. This implies that the voltage across the secondary plane is V_S = V_s2, hence V_oc = V_s2/N across the primary plane.

4.11. Repeat for the following passage:

First let us assume thermal equilibrium with no externally applied voltage. Charge-carrier density gradients are set up by diffusion processes that occur across the junction region when it is formed. The immediate junction area consists of a depletion region characterized by a lack of mobile charge carriers; an associated electric field constitutes a built-in potential barrier with a contact potential of a few tenths of a volt (commonly 0.7 V). No net current flows across the junction in equilibrium; there is a precise balance between diffusion currents and “drift currents” caused by the junction field. The depletion region is also known as the space-charge region. It is around 0.5 μm thick, and has a junction capacitance typically in the low-pF range.

4.12. In addition to advancing sound arguments and providing clear descriptions, engineers have to develop and explain classifications. For example, chemical engineers classify aqueous solutions as acid or base, according to pH, but may also choose to further classify acids as either strong or weak, or as either organic or inorganic. Generate a slide that serves to classify some objects or ideas of interest to you. Practice the presentation to yourself, anticipating possible questions or objections.

4.13. On page 76 the following were cited as examples of mathematical carelessness. Precisely what is wrong with each one?

(a) M_s = 4πM_s

(b) w = ∑Nn=xn $w = \sum_{n =}^{N} x_{n}$

(d) ∫ cos x = sin x

(e) F → ma

(f) f(θ) = cos(theta)

4.14. Write out your favorite equation from physics or engineering, and practice explaining it without reading it symbol by symbol.

4.15. Linda is a sales engineer for ABC Corporation. Her job requires technical knowledge, but she is really the person that sells the product to her clients. One of Linda’s clients asks her to speak at his son’s high school. Are any ethical considerations involved here? Why or why not?

4.16. Build a presentation and construct a rubric to evaluate the result. You may wish to use the checklist from Section 4.8 as a guide. Attend the presentation of a speaker that you admire, and apply the rubric.

¹”Dr. Edward Teller’s Magnificent Obsession,” Life Magazine, p. 62, September 6, 1954.

² http://news.bbc.co.uk/2/hi/7702913.stm. Last viewed January 24, 2015.

³Remember, people have been giving engaging talks for millennia without using a single slide. Story-tellers have passed along oral history, philosophers have described difficult subject matter, and religious figures have explained detailed history and concepts, all without slides.

⁴ http://www.nsf.gov/bfa/dias/policy/rcr.jsp. Last viewed January 24, 2015.

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Table of Contents for 4 Building Your Presentation

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Table of Contents for
4 Building Your Presentation