Why would you pump a flat basketball?

Answer 1

As air fills the Basketball, the pressure expands outward to make the outside of the ball feel harder. The valve on the outside of the ball allows the pump to put air in prevents air from escaping.

Answer 2

Pressure is the ratio of mass per volume. Adding more air (mass) into the fixed volume of the ball increases the pressure inside it. A basketball cannot expand much even when the pressure inside is higher than the outside air.

Answer 3

The pressure increases, and the molecules collide with the ball's inner surface.

Answer 4

so that the air particles inside will move faster and the ball will be full.