What you need:
Coins (preferably of the same size)
A dinner knife
A table
What to do:
1. Stack the coins one atop the other on a steady table. Keep the coin tower as straight as you can. You can decide how high you want your tower to be.
2. Now, hold your dinner knife as flat against the table as possible. Carefully (and quickly), swipe the knife to remove the coin at the bottom of the tower.
What happens:
If you’re doing it right, the coin at the bottom should slide out, leaving the tower still standing! Repeat the swiping process to check how many coins you can knock out before your tower of money comes crashing down.
Why?
The famous scientist, Sir Isaac Newton, has put down a law that states ‘an object at rest stays at rest, or if it is in motion it will continue to move until it is acted on by an external force. This tendency of the object to maintain its state of rest or motion is called inertia. Simply put, it means that the coins in the stack will remain motionless where they are unless something causes them to move. That something is the force you apply with your knife. But when you try to move a coin slowly, the entire tower topples over.
You can blame friction for that. Friction is a resisting force that opposes the motion of one object’s surface over another. When you try to move the bottom coin slowly, friction acts between the surface of that coin and the one above it. So the bottom coin drags the one above it that coin pulls the next coin along and crash! That is why you need to swipe out the bottom coin as fast as possible. The force you apply is so fast and hard that it overcomes the friction force, causing the bottom coin to shoot out smoothly.
Picture Credit : Google
