How the Air Puck Works



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The puck moves on a cushion of air. The tube that supplies the air also includes a fine chain that is connected to a high voltage source called a spark timer. The voltage source produces a spark between the centre of the puck and the carbon paper at precise intervals. The sparks passing through the carbon paper leave a dot indicating the position of the puck at that instant. In this case, the elapsed time between dots is 50 ms(milliseconds), that is 0.050 s.

The track produced by the spark timer shows that the motion of the puck is symmetric. Near the top, on either side, the dots are very closely spaced. This indicates that the puck came to a momentary stop, it was motionless. Therefore, its kinetic energy is zero and, because it is at the top of its travel, the gravitational potential energy is at a maximum.

Near the bottom of the track the dots are spaced far apart, because the puck is moving fast. Therefore, its kinetic energy is at a maximum at the very bottom. The bottom of the swing is also the reference level for the gravitational potential energy, which means that the potential energy is at a minimum.

The spacing of the dots also indicate that this is an accelerated motion. The increase in distance between the dots towards the bottom indicates that the puck was accelerating, speeding up on the way down and slowing down on the way up. The symmetry of the track suggests that the acceleration is the same on both sides of centre.