Rotational Energy Conservation - Physics Demonstrations - Rotational Energy Conservation | Physics Undergraduate Labs

The spinning mass can become a projectile if the string breaks or a knot fails. Inspect string before each use. Ensure adequate clearance from students.

Purpose

Demonstrates conservation of angular momentum. A mass spins in a horizontal circle on a string; shortening the radius decreases $$I$$ and the angular velocity increases to conserve $L = I\omega$ . The dramatic speed-up (quadrupling $\omega$ when $$r$$ is halved) makes the $$r^2$$ dependence visually obvious.

Apparatus laid out on a table: a black snap-hook clip with keyring, white string running to an aluminum cylinder on one end, and a dark rubber or lead hanging mass attached near the clip

Figure 1: The apparatus: an aluminum cylinder (the spinning mass) connected by string through a snap-hook slider to a hanging mass that provides constant tension.

Cork on String through Slider

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Safety Warnings

Warning: Rotating Mass Hazard

Purpose