Which statement best describes a simple machine?

• A. A device that makes work easier by changing the size or direction of a force; lever, inclined plane, screw, wedge, pulley, wheel and axle.
• B. An energy form that is used up when a machine runs.
• C. A measure of how fast work is done.
• D. A type of chemical reaction that releases energy.

Answer: (A)

A simple machine is a device that makes work easier by changing the size or direction of a force. The listed examples—lever, inclined plane, screw, wedge, pulley, wheel and axle—fit this idea because each one lets you move a load with less effort or in a more convenient direction. Remember, a simple machine doesn’t create energy; it changes how you apply force, often trading force for distance or changing its direction. The other statements describe energy being used up, or the speed of doing work (power), or a chemical reaction, which aren’t descriptions of a simple machine.