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Phone Book Swing
Two phonebooks can hold thousands of pounds. How is this possible? A rigorous weight lifting regimen? Nope.
Friction is the force created when objects move—or try to move—across each other. The force of friction can be small, like sliding a hockey puck across the ice, or it can be huge, like trying to drag a couch (complete with your napping Uncle Bob) over a shag carpet.
There are two types of friction: kinetic (moving) and non-moving (static). The phone books holding up the swing are demonstrating STATIC friction, because they are not moving.
Friction depends on a couple key factors:
- How rough or slippery the touching surfaces are (a slippery banana peel on a slick linoleum floor versus rusty barbells on top of some really rough sand paper).
- How much weight is on each of the surfaces (a very small and slippery banana peel on a slick linoleum floor versus several hundred pounds of rusty barbells on a really rough piece of sand paper).
But, isn’t the paper in a phonebook smooth and more slippery than rough? Not really. Look at a photo of a piece of paper through a microscope, and you will see that the surface of a piece of paper is actually bumpy and irregular. Put two pieces of phonebook paper together and this roughness will give you a small frictional force. Squeeze thousands of pages against each other and you get an enormous frictional force…capable of holding several thousand pounds.
- Learn More About How Friction Works
- Take a Look at the Surface of a Piece of Paper Through a Microscope
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