Did you ever wonder...

    ...how ice skaters, divers, and gymnasts get themselves spinning and twisting faster?  You've probably seen an ice skater start to spin suddenly faster.  A diver or gymnast may also experience a sudden increase in speed by re-distributing their mass; bringing their arms toward their body.  A rotating object tends to keep rotating with a constant "angular momentum" unless it is acted upon by an outside force.  A person sitting on a rotating chair has angular velocity and inertia.  If you are initially rotating with your arms outstretched, when you draw your arms inward, your moment of inertia decreases and you spin faster.

You Try It!

• Sit in the chair with one of the weights in each hand and arms outstretched.
• Have a friend spin you around slowly and then let go and move away.
• Bring your arms slowly to your side.
• Be careful!  Don't get dizzy!

    This effect, called the conservation of angular momentum, explains why an ice skater starts to spin faster when he suddenly draws his arms inward, or why a diver or gymnast who decreases her moment of inertia by going into the "tuck" position starts to flip or twist at a faster rate.