Yo-Yo and Counterweight - Physics Demonstrations - Yo-Yo and Counterweight | Physics Undergraduate Labs

Purpose

Demonstrates how mechanical constraints produce counterintuitive motion. As the yo-yo unwinds and falls, its decreasing effective radius releases string, causing the balanced counterweight to descend rather than rise -- challenging students' Atwood machine intuitions.

Two bench clamp stands with pulleys on a horizontal rod; a blue yo-yo hangs on the left and a white counterweight on mass hanger hangs on the right, connected by string over the pulleys

Figure 1: Yo-yo (left) and counterweight on mass hanger (right) connected by string over two pulleys. When the yo-yo is wound up and released, both sides descend.