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Description:

This demonstration is proof that all objects without air resistance will fall at the same rate, regardless of their mass.

 


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Possible Incorporated Topics:

  • Constant acceleration
  • Air resistance
  • Gravitation



Theory:

Galileo was the first to discover that dropping two objects from the same height will result in them hitting the ground at the same instant if all air resistance is ignored. The effects of air resistance are most dramatically seen with the classic example of the feather and the bowling ball. The feather’s shape causes it to endure significantly more air resistance than the streamlined bowling ball does, and therefore the feather takes a much larger amount of time to fall to the ground than the bowling ball.

If this experiment were done in a vacuum, there would be no air to form resistance and both objects would fall with constant acceleration – acceleration due to gravity. In other words, all objects fall to earth with the same acceleration (g = 9.8m/s2) but other effects hinder this value.

This demonstration is done in a vacuum and shows the consistency of the acceleration due to gravity.

 


Apparatus:
  • Ball
  • Feather
  • Vacuum pump and connectors
  • Two long, securely sealed clear tubes
  • Smaller tube
  • Large sheet of wood
  • Object that will allow the apparatus to spin
 

Procedure:

Before beginning, it is best to make sure that all junctions are securely sealed; any leaks will allow air into the apparatus and ruin the demonstration by causing resistance! 

  1. With the apparatus in place, connect the vacuum pump to the valve and pump the air out of the tubes. The amount of time this takes will vary depending on the size of the tubes and the and strength of the pump. For our demonstrator it takes approximately 45 seconds.
  2. Close the valve on the apparatus and turn off the vacuum pump. Remove the vacuum tube from the valve.
  3. Spin the apparatus and watch the objects fall. It is best to do this step quickly so that neither object reaches the top of the spin first and gets a "head start" in falling. This may take some practice and is best to perfect before demonstrating for a class.


SAFETY WARNINGS:

  • Make sure no one is in the way of rotating apparatus as it may end up needing to be spun very quickly!
  • Always be careful when using a vacuum pump. Keeping it turned on for too long can damage the pump and the demonstration apparatus. Also, vacuuming all the air out of the tubes and subsequently releasing it puts stress on the tubes. It is therefore best to do this as few times as possible.