impact velocities and angles. The pendulum is raised to a set height and then drops due to gravity until it hits a horizontal stop-bar. The location of the bar that stops the pendulum as it swings down sets the projectile impact angle. Our pendulum setup is illustrated in Figure \[fig:pend\]. A photograph of the experimental setup is shown in Figure \[fig:setup\] and a close up view in Figure \[fig:setup\_close\]. An illustration of the sandbox, camera and lighting as viewed from above is shown in Figure \[fig:ric\_lighting\].

Prior to letting the pendulum drop, the marble is held up against a thin rubber washer. A red turkey baster handle is used to apply light suction to the marble to hold it in place. A light tap on the pendulum is enough to break the suction and eject the marble. Because the required tap is light, the marble suffers only a small reduction in velocity during ejection. The marble is ejected with some backspin (angular rotation rate $\sim -30$ rad s$^{-1}$), that is usually well below the size of the horizontal velocity component divided by marble radius ($\sim $ 100 to 300 rad s$^{-1}$). Backspin is larger than expected from the pendulum swing 