Figure 21-2: Length Contraction and Time Dilation (a) The faster an object moves, the shorter it becomes along its direction of motion. Speed has no effect on the object’s dimensions perpendicular to the direction of motion. (b) The faster a clock moves, the slower it runs. This graph shows how many seconds (as measured on your clock) it takes a clock that moves relative to you to tick off 1 second. The effect is pronounced only for speeds near the speed of light c.