What is a simple machine?

• A. A device with many moving parts that increases work.
• B. A complex engine.
• C. A device with few moving parts that makes work easier.
• D. A machine that operates only in space.

Answer: (C)

Simple machines change the size or direction of a force so you can do work more easily, and they usually have only a few moving parts. The description that fits this idea best is a device with few moving parts that makes work easier. That captures both the simple design and the helper effect, since you can apply a smaller force over a longer distance to accomplish the same task. Examples include levers, inclined planes, pulleys, screws, wedges, and wheels and axles. The other options describe more complex or irrelevant ideas—for instance, more parts and increased work, a complex engine, or something that only functions in space—so they don’t match what a simple machine is.