THE SIMPLE ROLLER COASTER

The simple roller coaster started with Galileo Galilei. Below is a description of how to demonstrate Galileo's experiment using the Roller Coaster Simulator. [This experiment could also be duplicated using a HotWheels™ track and a marble.]



This has far-reaching implications. (1) The marble could take any path until it reaches the same height it starts from, assuming no friction. In the previous activity, the marble did not roll to the same height it started from because of friction. But it consistently rolls to the same height. To reflect these implications, the track could be reshaped as shown below.

(2) The ball begins to roll down due to the force of gravity. It stops when all the energy gravity gave the ball is used up. The marble accelerates only while a force acts on it in its direction of motion.

Here is a good exercise to draw on a chalk board.

The acceleration can be demonstrated experimentally using the roller coaster simulator or HotWheels™ track. If a long enough section is made horizontal, it can be shown that the average velocities calculated at the beginning and at the end of the horizontal section are equal. Form the track in the shape shown below. Roll a marble or steel bearing down the track. It will accelerate along the drop and move at a constant velocity along the horizontal section and slow down as it climbs up the opposite side. When the marble slows down and speeds up on the hills it is visually obvious. What is not so visually obvious is what happens along the horizontal section of the track. The ball's constant velocity can be shown mathematically. Divide the horizontal section of the track into 2 sections. Calculate the average velocity of the ball along these two sections. If done accurately, the velocities will be nearly equal. To obtain more accurate results, use fairly long sections of horizontal track. The longer the sections of track, the greater the time measurement. Longer time measurements mean lower percent errors.

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Along the horizontal section of the track, ignoring the minimal effects of friction, there are no forces acting on the ball horizontally. Therefore the ball moves at a constant velocity while no force acts on it. This is Galileo's law of inertia!!!

The ball continues until it reaches the starting height.