So let me try to explain a little bit. Lets say I have a robot on wheels. I want this robot to push a block. Lets say the force to produce in order to move that block is 100N.

How much energy will I need in order to begin pushing this block?

My dilemma is, Nothing is moving, therefore no work is being produced therefore no energy... But when I push something myself, I'm obviously using energy. But how do I produce force with energy if nothing moves.


Many students confuse the term work in physics with the conventional term of work. Your body wastes energy when you push something, and when that something doesn't move... 100% is wasted in the biological efficiency. 1st step: forget the concept of how hard it would be for you to do it.

How much work is a table doing by holding up a 1kg weight? zero. It has little to do with the fact it would be heavy and tiring for you to hold.

When you push a wall and it doesn't move, it is the same as if you leaned a filing cabinet on the wall. nothing moves, no work.

Your question "How much energy will I need in order to begin pushing this block?" is invalid. The question is how much force... and that is 100N. The energy applies in pushing it a certain distance. The power is how fast it will move.

  • $\begingroup$ Just the kind of remark I was thinking on making, in particular the first paragraph! $\endgroup$ – Ignacio Vergara Kausel Jul 16 '14 at 15:05
  • $\begingroup$ Hmm, I didn't really confuse the terms although I understand why you bring it up. I know no work is produced, because the equation W = Fd, implies that it's force over distance. But how can you produce force without using energy? $\endgroup$ – user3471141 Jul 17 '14 at 1:05
  • $\begingroup$ For example. If I had a robot continuously move. It hits a block, but can not move it until I give it more power. Mathematically, how can I tell how much power I need to supply enough force to push the block $\endgroup$ – user3471141 Jul 17 '14 at 2:14
  • $\begingroup$ Your question is still flawed. A very tiny amount of power, combined with the mechanical advantage of gears can in theory move an enormous block, but very slowly. $\endgroup$ – Michael Jul 17 '14 at 13:30
  • $\begingroup$ You're real question is how much power does it take to make your robot produce 100N. That is all in the electrical and mechanical design of the robot. You need to tell us the mechanical gearing to the wheels, and torque curve of the motor, and the resistance of the windings and then maybe we can work out the minimal power to just reach 100N. To be clear, the "Power to produce 100N" is all the energy losses in the system, not a simple Newtonian calculation that you seem to be looking for. $\endgroup$ – Michael Jul 17 '14 at 13:31

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