Me. give an everyday example of an action and reaction pair that does produce motion and one that does not.

An example of producing motion would be two billiard balls colliding. One's force would cause a reaction with the second ball that would move. Without motion would be one where you could be pushing a fridge but because you are not strong enough, the fridge doesn't move. The fridge's reaction is actually pushed back to you, and that is the action-reaction.

The center is basically the heart of it