Why does the tension force in a pendulum's string not do work on the pendulum?

The tension force in a pendulum's string does not do work on the pendulum primarily because the tension force is always directed toward the pivot point, which is how it maintains the pendulum's arc-like motion. When an object is in motion, work is done when a force causes the object to move in the direction of that force. In the case of the tension in the string, it acts perpendicular to the direction of the pendulum's displacement at every point in its swinging motion.

Since work is calculated as the product of the force applied and the distance moved in the direction of that force (work = force × distance × cos(θ)), and since the angle θ between the tension force and the direction of motion is 90 degrees (where cos(90°) = 0), the work done by the tension force is zero. This is a crucial concept in understanding the dynamics of oscillatory motion, as it highlights the role of different forces in a system and how they contribute (or don’t contribute) to the system's energy.

In contrast, other choices do not accurately describe why no work is done by the tension force. For instance, whether the string is too heavy or only acts at rest positions doesn't fundamentally affect the