Why does the air pressure increase when you pump a tire?

When you pump air into a tire, you are increasing the number of air molecules inside the tire's confined space. As more air is added, these molecules collide more frequently with the tire walls, leading to an increase in pressure. This rise in air pressure is a result of the gas laws, specifically Boyle's law, which states that at a constant temperature, the pressure of a gas increases as its volume decreases. Therefore, the confined volume of the tire limits the space for the air, resulting in higher pressure.