Define what acceleration means.
A steel ball with diameter $0.080\,\text{m}$ is let go from rest and drops vertically through air, as shown in Fig. 2.1. A horizontal light beam of negligible width is $0.280\,\text{m}$ vertically below the bottom of the ball at the instant it is released. As the ball falls, it passes through and interrupts the beam.
Explain why the force due to air resistance on the ball can be ignored when finding the time for the ball to reach the beam of light.
Calculate the time for the ball to fall from rest to position $P$ at which the bottom of the ball just touches the beam of light.
Determine the time interval for which the ball breaks the beam of light.
A different ball is released from the same position as the steel ball in (b). It has the same diameter but a much lower density. For this ball, the force due to air resistance cannot be ignored while it falls. State and explain the change, if any, to the time interval for which the ball breaks the beam of light.