Which of the following describes an example of uniform circular motion?

Correct Answer: A fan blade rotating at constant speed

Understanding Uniform Circular Motion:

Uniform circular motion is defined as the motion of an object traveling along a circular path at a constant speed.

Let us analyze the key requirements for uniform circular motion:

1. The trajectory or path must be circular.

2. The magnitude of the velocity, which is the speed $v$, must remain constant throughout the motion.

Evaluating the Given Options:

1. A train moving on its track: This generally represents linear or straight-line motion (or motion along arbitrary curves), not continuous uniform circular motion.

2. A car accelerating on its way: Since the car is accelerating, its speed is changing over time. Therefore, it is not moving at a constant speed.

3. A ball thrown vertically upwards: The ball travels in a straight vertical line under the influence of gravity, so its speed changes continuously and its path is not circular.

4. A fan blade rotating at constant speed: Any specific point on a rotating fan blade moves along a circular path around the central axis. When the fan operates at a fixed setting, it spins at a steady, unchanging speed. Thus, this is a classic example of uniform circular motion.