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The Question

(Submitted November 17, 1997)

I am in 8th grade. I have to do a science project and I am really looking forward doing it. I really want to do something that has to do with physics especially gravitation, inertia, or relativity but I must be able to test it. Can you please help me get a topic that might take my science project all the way to state science fair?

The Answer

I don't know whether this will get you to the state Science Fair, but you could do something based on this common lecture demonstration.

Needed :

  • 2 lengths of sewing thread
  • 500g (1 lb) weight
  • a tall overhang to tie the string from

Tie one string from the overhang (like a hangman's gallows) onto the weight.

tie second string from weight toward floor.

           -----|
           |    |
  string 1 |   	|
	   |	|
  weight  {-}	|
	   | 	|
  string 2 |	|
       	   |	|
	   |	|
	  	|
		|
		|
     -----------------
Now if you pull the bottom string slowly the top string will break (your force + the force of gravity on the weight). If you jerk the bottom string down quickly it will break (the inertia of the weight will not give the impulse force enough time to put tension on the top string)

David Palmer and Michael Arida
for Ask an Astrophysicist

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