# Friction

Friction is the slowing down of a moving object because it is touching another object. Newton said that objects in motion tend to stay in motion and they do. In a vacuum, or in a place with nothing, if an object were put into motion it would never stop. In space objects keep moving at their original speed forever or until they collide with another object. But on earth we have friction to slow us down.

A homemade hovercraft reduces then friction below the vehicle dramatically.

Look for places around your house where friction is an issue. Consider cars, bicycles, the bathtub (don’t want to slip), the outside walk when it’s wet or icy, the spinning drum in your dryer, and many more. In some places we want friction and in others we don’t. How do we overcome the friction problems in each of the places you found around your home?

Wheels are a way to overcome friction. Think about how a wheel reduces the friction and makes it easier to move an object vs. dragging it across the ground. Pick a heavy object and try to move it by first dragging it, then by putting it in a wagon or wheel barrow to move it. Which is easier?

Here are some friction experiments to try:

## Sandpaper vs. Smooth

Get an object like a block of wood or a bar of soap. Attach a string to it. Pull it across a smooth surface, like your counter top then pull it across a rough surface, like a piece of sandpaper.

• Which was easier to move across?
• Can you think of ways to reduce the friction on the counter to make it slide even more easily?

## Air has friction too

. . . But it has much less than a solid surface. Make a balloon hovercraft to demonstrate this.

You need a balloon, an old CD, a spool, like from sewing thread, and some glue, like Gorilla Glue or super glue.

1. Glue the spool directly to the CD, lining it up with the hole.
2. Let the glue dry.
3. Now put the end of the balloon over the spool.
4. Blow up the balloon through the spool.
5. Let it go, CD down, on a smooth surface.
6. The CD will skate all over the surface until the balloon runs out of air.

## Friction Increases as Speed Increases

Rub your hands together slowly, pressing them into each other.  Can you feel the resistance between your hands?  That is friction.

Now rub them very quickly together. You’ll feel your hands getting hot. The friction produces heat.