* The ball itself expands: As you pump more air into the ball, the internal pressure increases. This pressure pushes against the elastic material of the ball, causing it to stretch and expand. The volume of the *ball* increases to accommodate the extra air.
* Density increases: While the volume of the ball increases, the *volume of air itself* does not change. What actually happens is that you are packing more air molecules into the same space, making the air inside the ball denser.
Think of it like this:
Imagine a balloon. You can blow more air into the balloon and it will get bigger. The volume of the balloon increases, but the amount of air you actually blew into it remains the same. You've just compressed those air molecules into a smaller space.
The same principle applies to a basketball or any other inflatable ball. The ball itself expands, but the total volume of air you've pumped in stays constant. You're just increasing the density of the air within the ball.
