the sand tray is leveled in directions parallel and perpendicular to the marble launcher using a bubble level.

The pendulum itself is $L=94.8$ cm long, but the radial distance from pivot to marble ejection point is $L_m = 84.3$ cm long. Due to its extended mass distribution, the pendulum is a compound pendulum. We measured the moment of inertia of the pendulum from its period of small oscillations ($T=1.78$ s) and its center of mass radius from the pivot, $R_{cm} = 50.5$ cm using the relation $$\frac{I_{pend}}{M_{pend}} = \frac {T^2}{(2\pi)^2} g R_{cm}$$ where $M_{pend}$ and $I_{pend}$ are the mass and moment of inertia (about the pivot point) of the pendulum. Measurements of the pendulum are listed in Table \[tab:pend\]. The inside dimensions of the sandbox are 87.5 cm long, 11.5 cm wide and 6.3 cm deep.

![Side-view illustrations of our pendulum based marble launcher. The pendulum is dropped from a height $h$, setting the velocity of impact. The pendulum swing is stopped by a stop-bar at an angle $\theta_{sb}$ that sets the angle of impact. The marble is ejected from its holder when the pendulum is stopped and then hits the sand. The red bulb is used to apply a 