Physics Learning Tool

Angular Momentum: Spinning Skater

Move the skater's arms inward or outward and watch how moment of inertia, spin speed, and angular momentum change together.

Big idea: angular momentum remains constant when the net external torque is zero. A skater can spin faster by pulling mass closer to the rotation axis.

Interactive Angular Momentum Simulation

Explore the same rotation from above and from the side. Move the arms to change the distribution of mass.

Ready

Direction guide: in the top view, ⊗ means angular momentum points into the page and ⊙ means it points out of the page.

Live Results

Blue: spin speed ω Purple: angular momentum L Green: radius r Yellow: hand weights

Arm PositionMedium

Value adjusted to the safe range.

Skater Mass45 kg

Value adjusted to the safe range.

Hand Weight Mass2 kg

Value adjusted to the safe range.

Initial Spin Speed Angular velocity tells how fast the skater rotates, measured in radians per second. 2.2 rad/s

Value adjusted to the safe range.

Rotation DirectionClockwise

Conservation mode: keep angular momentum constant Show labels Show motion trail

What Just Happened?

Move the arm-position slider, make a prediction, then press Play.

Direction Check

Viewed from above, clockwise rotation gives angular momentum into the page. The side view shows that same direction as a downward arrow through the skater.

See the Physics

L = IωAngular momentum equals moment of inertia times angular velocity.

Star 0

Make a Prediction

Choose an answer, then check your prediction.

What Students Should Remember

Mass far from the axis matters

When the skater's arms are out, more mass is spread away from the centre, so moment of inertia is larger.

Spin speed adjusts

With little external torque, pulling arms inward lowers moment of inertia and increases angular velocity.

Direction uses the right hand

Curl your fingers with the rotation. Your thumb points in the angular momentum direction.