Study of a rolling ball

A large ball bearing or 'bagatelle ball' rolling down a smooth track can be timed by a pendulum. To make the track, fasten together two 120 cm lengths of glass tubing (or other smooth rods) with rubber bands. Place them on a length of wood resting on a table, with a matchbox under one end. Set up a simple pendulum to give about quarter second time intervals. A metal nut carried by cotton is suitable. Begin the ball rolling down the track and observe its position after successive swings of the pendulum. Make marks along the wood opposite the position of the ball at equivalent time intervals.