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Why do figure skaters spin so fast?

Submitted by Andrew Smith on Tue, 09/11/2018 - 15:46

In this experiment, middle school and high school students use their PocketLabs learn about angular velocity -- the rate of change of angular position of a rotating body.

Other physics classroom activities on this topic explore momentum, like in this experiment, as well as the moment of inertia, like in this experiment.

This experiment corresponds with NGSS unit "K - Forces and Interactions: Pushes and Pulls."

Learn more about motion and inertia in this PDF from Hooked on Science.

TOPICS: Angular Velocity, Momentum, Inertia

Use a swivel chair for a physics experiment in angular velocity. Suitable for middle school and high school students.

STEP ONE

  • Tape your PocketLab to the back of a swivel chair, close to the y-axis.
  • Select the ANGULAR VELOCITY setting

 

STEP TWO

  • Sit in the swivel chair.
  • Tuck in your feet (so they don't touch the ground) and pull your arms close to your chest.

 

STEP THREE

  • Ask a friend or classmate to spin you in the swivel chair.
  • As you are spinning, stretch your arms out from your chest.
  • Does it feel faster or slower?
  • Examine your PocketLab data. Were you actually spinning faster or slower?

 

BONUS

  • Stretch your arms in different directions -- including all the way up, parallel to your body.
  • Stretch out your feet.
  • Spin in different directions.
  • Start a spin faster and slower than the original spin.
  • Hold a heavy object in your lap.
  • When you stretch out your arms, hold something heavy in one hand. Try the other. Try both.

 

What is angular velocity?

When a figure skater spins, the skater positions her or his arms to control the speed of the spin -- the angular velocity. As you stretch your arms and feet, you distribute your mass across a larger area, spinning more slowly.

Try this experiment in angular velocity. Why do figure skaters spin so fast?

 

The angular momentum of the skater is always conserved, no matter the positioning of the arms, and can be represented by the equation --

L = Iw

 

-- where L is angular momentum, I is moment of inertia and w is angular velocity.

The moment of inertia is an object’s resistance to change in angular velocity and is related to the distribution of the object’s mass.

In this physics experiment, learn why this male figure skater spins so fast.
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