Why does compressing a gas increase its internal energy?

The correct answer is Because work is done on the gas..

Application lens: Apply the rule to the specific sample or situation instead of reciting a broad fact. This question asks: Why does compressing a gas increase its internal energy. The correct response is Because work is done on the gas., because gas pressure comes from particle collisions with container walls. In Increasing the pressure of a gas (physics only) (HT only), the marking point should connect directly to (Physics only) (HT only) Explain why a gas may get hotter when it is compressed quickly. If the question includes values, the working must keep the appropriate unit and operation; if it is an explanation, it must name the relevant particle behaviour or energy change. This item belongs to Particle model and pressure, so avoid answers that switch to a different quantity, confuse heat with temperature, or describe gas pressure without collisions when collisions are the reason. Checkpoint 607 is distinct because it uses this exact question context and the application lens rather than a generic particle-model sentence.