Extreme Science: Penny Shine

What you will need:

  • Hot wheels tracks
  • (2) Golf balls (or similar size)
  • Adult supervision

Procedure:

  1. Set up your tracks so that you have two tracks that are side by side.  Both tracks need to be set up so that they are curved just as the path that a ball on a pendulum would take as shown:

    Note: You may want to use a string and a pencil to draw a ¼ circle on a piece of cardboard or something that you can cut out to help hold your track on this (pendulum) curve as shown:
  2. Place a ball on each track and release them at the same time.  Both balls should hit the bottom of the tracks at the same time.  Now, try placing the balls at different spots on each track and release them again at the same time.  If you track has the right curvature, they should both hit the bottom of the track at the same time regardless of where they started from.
  3. Now try placing two tracks side by side with no curve (as shown) and try the experiment again.

What is going on?

You will find that when you place the balls on the curved track, both balls will reach the bottom of the track at the same time, regardless of where you start them.  On the other hand, when you place the balls on the straight tracks, they will only reach the bottom at the same time IF you start them at the same height on the track.  When you release the balls from different spots on the straight track, the balls that is lower on the track will always reach the bottom first.

When you release the balls on the straight track, the angle of the track is the same regardless of where the balls start.  This will cause both balls to speed up at the same rate no matter where they start from.  Notice how the angle of the curved track is different at every spot on the track.  The higher you go on the curved track, the steeper the angle.  This causes the ball to speed up faster when it is released towards the top of the track allowing it to travel a greater distance in a shorter amount of time.  Thus, the balls released towards the bottom of the track move a lot slower.

Try this:

Try making two pendulums that are the same length right next to each other.  Now, pull both of them back the same distance and release both of them at the same time.  Both pendulums will swing at the same rate and take the same amount of time for a full swing, or rotation.  Now, try pulling one of them back twice as far as the other and release both of them at the same time again.  You will find that the results are the same.  Both pendulums will take the same amount of time to complete a full swing, or rotation.

Radical Rick

Extreme Science

www.ExtremeScienceFun.com

509-892-7621

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