What is a pulley?

• A. A device that amplifies energy through friction
• B. A machine that supports movement and changes the direction of force
• C. A type of lever that has a fixed length
• D. A simple machine that uses hydraulic principles

Answer: (B)

A pulley is defined as a machine that supports movement and changes the direction of force. This explanation stems from its fundamental design and function: a pulley consists of a wheel on an axle or shaft that is designed to support the change in direction of force applied to a rope or cable running along its circumference. When you pull down on one side of the rope, the other side goes up, allowing for easier lifting of objects, making it a practical tool for many applications, such as in construction and transport.

In contrast, other options describe concepts that do not accurately capture the essence of what a pulley is. For example, amplifying energy through friction might refer to a different type of mechanical system, and the concept of a lever implies a different mechanical advantage based on distance from the fulcrum. Similarly, hydraulics pertain to fluid dynamics, which is not related to the functionality of a standard pulley. Thus, option B accurately and comprehensively encapsulates the core purpose of a pulley in simple machine terminology.