Let's say we do a push up. If asked to compute the work, it would be Mass(lifted) x G(gravity) x height moved. I get that.
What confuses me is how/what force does the work?
Part of me feels it would be the ground, because as we push down, the ground pushes back forcing us up. However, this makes no sense as the ground has no energy to give and the distance at the point of application is zero.
So that must mean the work is done by the muscles. But how so? Really yes the muscles start pushing down, which causes the ground to push back, making the muscles internally then push up and move the body, hence we say the person/muscles did the work.
I never thought of it before. If I think of it as the muscles pushing the body up, obviously this is not an issue. But I realized for the muscles to push up, they must push the ground too, which doesn't move.
Sorry if this is repetitive, I am really confused. Thank you for the help
Best Answer
Essentially the force from the ground just acts as an energy converter (here from chemical to mechanical) and in due process you neither gain nor lose any amount of energy (assuming that dissipation in the form of heat is negligible). A similar case is of walking where frictional force converts your chemical energy into your kinetic energy. During the whole process the ground neither gains nor loses the energy (assuming that there is negligible change in earths rotatory motion).