Time travel thread, Hey ho let's go!

How? It's like this: consider a rapidly rotating wheel. All the parts of it are going round in circles. Newton says that to deviate from straight uniform motion you have to be accelerated by some net force. In this case all the bits of the wheel need to be being pulled towards the middle of the wheel to make them go round in circles. If the wheel is symmetrical, these forces all balance out so when you hold the wheel by its axle, all you feel is its weight. But if you try to rotate the axis of the wheel in a different way from the way it's already spinning you feel a load of extra forces. Say you are holding the axle horizontal in front of you, the wheel is spinning so that the top is moving away from you, and you try to turn the axle to your left: the parts of the wheel are already going round in circles, they can't go round different circles at the same time, so they actually follow more complicated paths. As the axle turns, the bits of the wheel going along the top and bottom have to change direction sideways to remain part of the wheel. The bits going away from you along the top have to be accelerated to the left, and the bits coming towards you on the bottom have to follow curves that bend to the right. The forces to achieve these accelerations might be equal, but they don't line up, so they don't cancel out and you have to supply them (as a twist, bottom right, top left -> left hand down, right hand up) in order to make the wheel's axle rotate to the left.

This is all very well and nice, Tom, in its long-windedness and all. But what you're really trying to say can be put a good deal more succinctly:

"DON'T LEAN!"