Teach Fzx - Spinning Ladies and Disappearing Inertia

You're traveling down the street at 10 mph on your bicycle and BOOM - half of your mass disappears.  I mean straight vaporized - and not just vaporized but annihilated.  But not even annihilated - that mass (inertia) is just no longer even part of the universe.

Right after that BOOM, suddenly you're going 20 mph since half your inertia disappeared but momentum is still conserved - so you have to be going twice the speed.  Crazy, right?

The above situation is, of course, impossible, but that's basically what's happening when all the spinning ladies on ice at Sochi speed up when they pull their arms in.  That's why gymnasts and divers tuck to spin faster.  They lose rotational inertia - it disappears from the universe - and they speed up since rotational momentum is conserved.

The opposite process is also true.  Spinning skaters slow down when they extend their arms and flipping gymnasts seem almost to stop when they fully extend.

We live in a world where you can lose or gain rotational inertia simply by changing your body orientation or the location of your arms and legs.  We spin faster when we lose rotational inertia; slower when we gain it.

The same does not apply to linear momentum and linear inertia (mass).  But imagine what'd happen if linear and rotational were the same.  Imagine and learn.