Rotational Motion · Interactive

Angular Momentum — Spinning Disc

Change a spinning body's moment of inertia and watch its spin rate answer instantly. Like a skater pulling their arms in, sliding the masses inward drops I and spikes ω — while L = Iω stays locked. Rotational KE, though, is not conserved: the skater does the work.

↻ Spin ω ● Point masses ▮ KE gauge Top-down view · L conserved

Setup

Arm radius r 0.70 m
Point mass m 2.0 kg
Platform M 4.0 kg
Platform radius R 0.70 m
Initial spin ω₀ 6.0 rad/s
6.00
Angular velocity ω (rad/s)
2.9
I (kg·m²)
6.0
ω (rad/s)
17.3
L = Iω (const)
52.0
KE_rot (J)
L = Iω conserved pull in → I↓ → ω↑ KE = ½Iω²

Playback

Try this: pull the arms all the way in (r → 0.15) and watch ω spike while L holds steady. Then hit Drop disc I₂: a still disc lands on top, they lock into a common ω — L survives but KE takes a hit.