In kinetic theory, what is the origin of gas pressure?

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In kinetic theory, gas pressure comes from the collisions of gas particles with the container walls. Each collision transfers momentum to the wall, producing a small outward force; when you have billions of particles colliding trillions of times per second, these impulses add up to a measurable pressure on all the inner surfaces. The speed and frequency of these collisions, which determine the magnitude of the pressure, depend on temperature: higher temperature means higher average kinetic energy, so particles strike the walls more forcefully and more often, increasing pressure at a given volume. Intermolecular attractions matter in real gases and can affect how particles interact, but in the ideal-gas picture the pressure origins are the wall collisions. Gravity mainly influences how gas density varies with height and is not the microscopic source of pressure in a uniform, fixed-volume container.