Final answer:
The pressure inside a pool floatie increases when air is blown into it because the added air molecules have less space, leading to more collisions and greater pressure inside the confined space of the floatie.
Step-by-step explanation:
When you blow air into a pool floatie, the air molecules inside the floatie become compressed as more molecules are introduced into a confined space. This compression of air molecules increases the frequency at which they strike the inside walls of the floatie, resulting in an increased force applied over the internal surface area. According to principles of physics, especially Boyle's Law, an increase in the number of air molecules, while the volume remains constant, leads to an increase in pressure.
The phenomenon is similar to what happens within a gas canister when air is pumped into it. The enclosed space limits the volume, so the more molecules you add, the higher the pressure becomes. In the case of the pool floatie, it is flexible but still has a limited volume, so as you continue to blow air into it, the internal pressure continues to rise until it reaches an equilibrium with the force of the air you're blowing or until the floatie is fully inflated.
In summary, the pressure inside the floatie increases because the additional air molecules have less space to move around, leading to greater collision frequency within the confined space of the floatie. This is an application of the gas laws, which relate pressure, volume, and temperature in scenarios where gases are involved.