A top is spinning with it's vertex Q in contact with a rough horizontal floor so that the vertex does not move. Why reaction at Q does no work?

Question

theeric · Answer

Work can be $F\ d\ \cos(\theta)$.

The reaction force is just the reaction to the top's weight. By Newton's Third Law, forces come in pairs! Now, if there is no movement in the direction of the force, the force has done no work! No movement at all, also implies no work. 

Any questions?

gorica · Answer

I think the last sentence explained all to me :)

theeric · Answer

Cool! :) Take care!