Final answer:
A gear is an example of a rigid body because it maintains its shape and size when external forces are applied to it.
Step-by-step explanation:
A rigid body is an object that does not deform under the actions of external forces. An example of a rigid body is a gear. Gears are used in many mechanical systems, such as machinery and vehicles, and they maintain their shape and size when external forces are applied to them. Unlike a hydraulic system, spring, or elastic belt, gears do not change shape or deform under external forces.