I'm a little confused about what exactly work/energy is. I understand that if I exert 10 N o a box over a distance of 10 m, 100 J of energy are expended. However, say I exert 10 N on a 100 kg box, and it does not move, why is no energy expended? Such an action certainly requires energy?

 PhysOrg.com physics news on PhysOrg.com >> Iron-platinum alloys could be new-generation hard drives>> Lab sets a new record for creating heralded photons>> Breakthrough calls time on bootleg booze
 Energy is transferred in the form of chemical reactions in your body that fuel your exerting of force. However, no work is done on the 100-kg box due to the fact that there is no movement. The force of static friction counteracts the force you exert.
 First, realize that physicists have a very specific mathematical meaning of "work" and "energy" and they are not the same as "effort". You should meditate on the case of a table. A table can hold things up indefinitely without expending any energy at all. No energy is required, because while the table is pushing up on the object, the object isn't moving, so no work is being done. It may be tiring to hold the same object stationary in your outstretched palm, but that doesn't mean that your palm is doing work *on the object,* any more than the table is doing work on the object when it supports the object. You get tired because the biology of your muscles is such that they need to burn fuel just to create a force in the first place. If the object doesn't move, your muscles burn chemical fuel, releasing energy, but that energy just ends up heating up your muscles instead of doing work on the object.

Recognitions:
Gold Member