Final answer:
When you move your head from side to side while watching a tennis match, the people on the other side of the court will appear to move faster due to parallax.
Step-by-step explanation:
When you keep your eyes on the net but move your head from side to side while watching a tennis match, the people on the other side of the court will appear to move faster. This phenomenon can be explained by the concept of parallax. Parallax is the apparent shift in the position of an object when viewed from different perspectives.
When you move your head from side to side, the people on the other side of the court will appear to move greater distances compared to objects that are closer to you, such as the net. This is because the closer objects have a smaller parallax angle, while the people on the other side of the court have a larger parallax angle. As a result, it gives the perception that the people are moving faster.