Why do gas particles collide with the walls of their container?

The correct answer is Because they are moving in constant random motion.

Practical lens: Link apparatus, readings, and uncertainty to the exact measurement named in the objective. This question asks: Why do gas particles collide with the walls of their container. The correct response is Because they are moving in constant random motion, because gas pressure comes from particle collisions with container walls. In Particle motion in gases, the marking point should connect directly to explain that the force from particle collisions produces gas pressure. 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 470 is distinct because it uses this exact question context and the practical lens rather than a generic particle-model sentence.