## Essential University Physics: Volume 1 (3rd Edition)

The apparent weightlessness of the ball has to do with the gravitational force acting on the ball. In this sense, the ball appears to have no $\underline{mass}$. However, what causes the ball to hurt is $\underline {inertia}$, which measures how hard it is to move the object. Therefore, the ball will still hurt to kick even though it appears to be weightless.