Scrolling in web applications is done by using the mouse pointer to drag the scrollbar back and forth or up and down, or by spinning the mousewheel. This doesn't work on a mobile device because there's no mouse. Everything is controlled by gestures on the screen. For example, if you want to scroll down, you use your thumb or index finger to pull the content up by physically moving your finger on the screen.

Scrolling like this is difficult to implement, but it gets more complicated. When you scroll on a mobile screen, the velocity of the dragging motion is taken into consideration. You drag the screen fast, then let go, and the screen will continue to scroll based on how fast you moved. You can also touch the screen ...