Say you compress a closed container full of gas (you reduce its volume). You are not holding the pressure constant or anything. As you do this, the temperature increases, but why? My best guesses are: - some of the energy you use for pressing down on the container is transferred to heat energy and thus increasing the temperature (?) - the force exerted on pushing the container down is passed onto colliding particles, thus increasing their kinetic energy But these two explanations would only increase the average kinetic energy by a small amount, if at all. Is there an explanation for this using kinetic theory?