The Atwood machine belongs to the class of machines that includes block and tackle systems. What is this class?

• A. Levers
• B. Pulley systems
• C. Inclined planes
• D. Screws

Answer: (B)

Pulley systems are devices that use wheels with grooves to redirect force and, with multiple pulleys, to gain mechanical advantage. The Atwood machine fits this category because it uses a rope passing over a pulley to connect two masses, letting them accelerate while the pulley changes the direction of the force. Block and tackle are simply multiple pulleys arranged to increase the mechanical advantage, all within the same pulley family. Levers, inclined planes, and screws are different kinds of simple machines that operate through a pivoted bar, a ramp, or threaded motion, respectively, and don’t describe this setup.