Thursday, October 16, 2014

Tackling Friction

Friction is a force that helps things slow down when they're moving. Friction is what makes your brakes work on your bike or car, and what helps a ball roll on the ground. But what happens when you want to have less friction? Try out this experiment and see if you can figure it out!

The Experiment

This experiment is based on a similar experiment by



Try it out:

  1. Ask an adult to help you cut a small hole on one side of the box. This is where the end of the balloon will stick out.
  2. Put the balloon through the hole so that the large part of the balloon is inside the box and the end is sticking out.
  3. Blow up the balloon, then hold the end closed with your fingers. Put the box on a flat surface, like the floor, and use tape to mark the starting point.
  4. Let go and measure how far the box travels. Try this a couple of times.
  5. Now cover the floor with straws like this. You'll need at least 3 feet of straws:

    6. Place the box and balloon on the straws and see how far they go this time.
    7. Finally, glue or tape two straws to the bottom of the box like a sled
Shoebox Sleigh
   8. Place the box and balloon back on the floor and see how far they go.

Which box went the farthest? Why do you think that is?

What's happening

Friction is a force that acts in the opposite direction as the direction something is moving. When the box moves forward, friction pulls it back. The stronger the friction is, the less the box can move.

What makes friction stronger? There are a couple of different things. One is how rough the surface is. A rough surface like carpet or the street will have more friction than a smooth surface like a wood floor. When you pushed the box on the lined up straws, the straws roll around and have very little friction because they are very smooth.

Another is the surface area of the object that is touching the floor. If the surface area of the object is bigger, that means the friction can push on a big area, which makes the friction stronger. When you glued the two straws on the bottom of the box, you gave the friction less surface area to push on. That makes the friction weaker so the box can move farther.

If you thought this was cool...

This experiment is related to mechanical engineering. You can find out more here.
Some ideas from physics in this experiment include forces and friction.

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