Conservation of Mechanical Energy

A bowling ball fastened at the end of a cord hanging from the ceiling of the classroom demonstrates the exchange between potential and kinetic energies.

A ball rolling on this track demonstrates the relationship among potential, kinetic and rotational energies. Loop-the-loop is a circular section of track with rails of metal tubing held together by metal cross ties. It is attached to two straight sections of similar track. The ends of the cross ties have threads that fit short support rods for use in supporting the track. Release the ball from one end of the track. The ball will orbit the track without losing contact and will reach the other end at the same height as it began.

The track used in this demonstration is mounted on a wooden board. It consists of an aluminum wide strip covering the board and two parallel sides a little wider than the ball used. One end of the track is clamped to heavy stands forming an inclined plane and it is set on the edge of a table. The ball is released twice from the top of the track. First, it is allowed to rotate. On the second time, it slides down the plane – the rotational movement can be inhibited by pulling out two small rods mounted on the sides of the ball, like wings, and setting it on the track. The “wings” should hold to the sides of the track. The whole class will see that when the ball does not rotate, it jumps further away from the table than when it rotates down the track.

This apparatus can be used to demonstrate topics of conservation of momentum and projectile motion. The pendulum swings freely at one end. When the ball hits the bob and swings it up, the bob is held at its highest point of the swing by a ratchet system. A protrusion at the base of the bob catches the ratchet which has a scale for measurement of height changes. For experiments on the range of the projectile, the pendulum can be swung out of the way so that the spring gun can fire the projectile horizontally into the air. The projectile can be fired at different velocites by the spring-gun, adjusting the spring’s tension. It also shows conservation of energy since potential energy is stored in the spring-loaded gun which becomes kinetic energy when the massive bob is fired, and is converted back to potential energy when it catches the ratchet.

It shows the conversion of potential energy into kinetic energy. Although the low road ball must travel a longer distance, it will be faster than the high road ball due to the conversion of gravitational potential energy into kinetic energy.

In a simple pendulum, the ball swings to the same height on each side of its rest position. If a bar interrupts its motion on one side, making the pendulum shorter, the ball still reaches the same height.