We define two classes of forces, namely conservative forces and non-conservative forces.
When we do work against non-conservative forces , then our work is dissipated in the form of heat, sound or light. When we do work against conservative forces, our work gets stored in the form of potential energy. What my doubt is that how does it get stored as potential energy
For example, consider the block and earth system , When I make the block move up slowly to a height $h$ , I do $mgh$ work on it, and the earth's gravitational field does $-mgh$ work on it. As a result, the $mgh$ energy goes from me to block and $mgh$ from block to the earth's gravitational field. There's no change in the kinetic energy of the block, but the energy of the gravitational field of the earth increases, and my chemical energy decreases.
The doubt that arises here is that the energy of the earth's gravitational field increases, then why do we say that the energy of the earth+block system increases.
Even if we say that energy goes to total field, then we can also say that block's gravitational field has done work on block which is false. What's the flaw in my reasoning here?
Best Answer
It is because gravitational potential energy, like all forms of potential energy, is a system property. Potential energy is the energy of the position of something relative to the position of something else. In the case of gravitational potential energy, is not the energy of the earth's gravitational field alone or the energy of the block alone, but the energy of the combination of the earth+block system.
Hope this helps.