In the kinetic molecular theory, what causes gas pressure?

• A. Volume of the gas particles.
• B. Gravitational pull on the gas.
• C. Temperature alone.
• D. Collisions of gas particles with the walls of the container.

Answer: (D)

Gas pressure comes from the constant, random motion of gas particles colliding with the container walls. Each collision transfers momentum to the wall, producing a tiny force; adding up countless collisions over the surface area gives the pressure. Temperature influences this by changing how fast the particles move (and thus how often and how violently they collide), but the direct cause of pressure is those wall collisions. Gravity and the actual size of the particles aren’t what creates the pressure in the kinetic picture, and the volume acts to change how often collisions happen rather than being the source of pressure itself.