Science Projects And Inventions

YOU NEED:

• Two cardboard rolls from a paper towel roll
• A ruler

Arrange the two cardboard rolls side by side and ,balance the ruler on top of the two as shown in the illustration.

If you happen to rotate the rolls inward, as indicated the arrows, the ruler remains balanced. It may shift back and forth slightly but it remains balanced. Even though it may move backwards and forwards.  It however remains balanced. Rotate the cardboard rolls in the opposite direction. The ruler will slowly travel to one side till it falls off the rolls.                   

HOW DOES IT WORK?       

The action that you have just noticed is the result of merger of weight and friction.

Take the case of the rolls rotating inwards. The moment the ruler moves a little bit to the left — its weight on the

cardboard roll increases. This naturally increases the friction between the ruler and the roll. With more friction

in the roll on the left than on the right, the moving left roll brings the ruler back to balance.