How is energy transferred from the bicycle wheel?

Michio Cuckoo

So check out the above video.

When the man flips the bicycle wheel over, the turntable he is sitting on starts to rotate. What I don't understand is, how is energy transferred from the bicycle wheel to the turntable?

A.T.

Energy isn't transferred from the bicycle wheel to the turntable. Just angular momentum.

Michio Cuckoo

But where does the turntable get the energy to rotate?

A.T.

From the muscles of the man.

HallsofIvy

In order to turn the wheel through a right angle, the man must apply force to ends of of the axle. You can trace trace the reaction force through the man's muscles and skeleton to his feet braced on the turn table (obviously, if he were standing on frictionless ice or in space, the motion would be different.)

A.T.

Yes, the forces (or rather torques) are transferring angular momentum from the wheel to the turn table. But there is no energy transferred from the wheel to the turn table.
On ice it would be quite similar to the turn table.

Michio Cuckoo

quite a sneaky transfer of energy. Thanks for explaining.

haruspex

So what happens if he flips the wheel back again? Presumably the man has to work just as hard, but now the turntable stops. Where has the energy gone?