I have a question regarding the conservation of energy. If I were to push a medium sized box across a surface, I would be imparting a certain amount of energy to it (and myself) and also dissipating a certain amount of thermal energy into the surface. This energy I'm supplying comes from the transfer of the chemically stored energy in my body when I push the box, yes? Now, if I were to expend an equal amount of bodily energy pushing against a large box, and was not able to overcome the friction force, would all that energy be instead dissipated as thermal energy into the ground and box? Maybe I'm just overestimating the awesomeness of kinetic energy, but intuition (often wrong, admittedly) tells me that the thermal energy produced in the second scenario would not be equivalent to the kinetic and thermal energy my efforts produced in the first. Apologies for a potentially dumb question, but could someone explain this?