What device is used to verify Newton's second law with hanging masses?

An Atwood machine is used to verify Newton’s second law with hanging masses. It consists of two masses connected by a string that passes over a pulley, allowing their acceleration to be measured and compared with the net force divided by total mass.

In the ideal setup, the string is massless and inextensible, and the pulley has no mass or friction. If one hanging mass is heavier, it moves downward while the other rises. Applying Newton’s second law to each mass gives an acceleration of a = g(m₁ − m₂)/(m₁ + m₂), assuming m₁ is the heavier mass.

George Atwood invented the apparatus in 1784. Its design made it possible to study constant acceleration more slowly and precisely than a freely falling object, whose motion changes too quickly for many early measurements. The machine therefore became a useful laboratory demonstration of classical mechanics.

A pulley system is a broad description, not the specific name of this experiment. The Atwood machine is also different from a ballistic pendulum, which measures projectile speed through momentum and energy changes.