As air is warmed, the particles (molecules) it is made up of spread out. The warm water heated the air in the ball. The warm air in the ball spread out (expanded) and pushed out the dent..

The student is able to communicate that the warm water heated the air in the ball. The air in the ball expanded and pushed out the dent. The student is able to communicate that warm air pushed out the dent. The student is able to communicate that warm water pushed out the dent. The student is able to communicate that the water pushed out the dent.