Which of the following does NOT define the motion of a pendulum swinging back and forth?

The correct option is "The pendulum exhibits uniform motion".

To understand why this is the correct answer, let us analyze the physics of a swinging pendulum step-by-step:

1. Understanding Uniform vs. Non-Uniform Motion:
Uniform motion is defined as the motion of an object covering equal distances in equal intervals of time. This implies that the velocity (both speed and direction) of the object remains constant throughout its motion. Conversely, non-uniform motion is when an object covers unequal distances in equal intervals of time, meaning its velocity is constantly changing.

2. Analyzing a Pendulum's Journey:
As a pendulum swings back and forth:
- At the highest points of its swing (the extreme positions), the pendulum momentarily comes to a complete stop, so its velocity becomes zero.
- As it moves down towards the lowest point (the mean position), gravity pulls it, causing it to speed up. Its speed reaches a maximum at the mean position.
- After passing the mean position, it climbs up towards the opposite extreme, slowing down until its velocity becomes zero again.

3. Evaluating the Options:
- Periodic Motion: The pendulum repeats its path of motion back and forth at regular intervals of time, which is the definition of periodic motion. Therefore, this defines the pendulum's motion.
- Accelerated Motion: Because the pendulum's velocity constantly changes in both magnitude (speeding up and slowing down) and direction, it is undergoing acceleration. Thus, it exhibits accelerated motion.
- Non-Uniform Motion: Since its speed is not constant, it covers unequal distances in equal time intervals, which defines non-uniform motion.
- Uniform Motion: Since the speed of the pendulum changes continuously during its swing, its motion is definitely not uniform.

Consequently, the statement "The pendulum exhibits uniform motion" does NOT define the motion of a swinging pendulum.