Stick Balancer

Find the centre.

 

 

 

Category - Force & Energy

Key Idea - Centre of Gravity

 

Purpose - A long thin object will balance on its centre of gravity.  Here is how to find it.
Nature -  Demonstration
Materials -  A metre ruler, a large lump of plasticine 
Method - 
  1. Placing your hand wide, balance the metre ruler on your the top of your index fingers.
  2. Slowly slide your hands together until they touch.  Notice that the ruler is balancing.  Note where your hands meet.
  3. Now attach the lump of plasticine to one end of the ruler, and try it again.  You should find that the rule again ends up balancing on your hands, however their location will have changed
Safety - Nil 
Explanation - The centre of gravity of and object is the point on which it balances.  When you balance an object on two fingers, the one closest to the centre of gravity will be taking slightly more weight.  When you start to slide your fingers towards each other one furthest from the centre of gravity slide easier (because of the slightly less friction). It will move along the stick until it is closer to the centre of gravity than the other finger, which now starts to slide.  This process see saws back and forth until both fingers are under the centre of gravity.
Notes - This works even if the centre of gravity is thrown off by an unevenly weighted object.