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Roll With The Changes (Friction)

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• Why do the tires on your bike roll better when they're all pumped up than when they're soft? And why do your roller blades go better on smooth pavement than on a sandy road? The answer is friction...the big rub! The force that slows you down and gets you going; without friction, you'd be slip slidin' away!

What To Do

This challenge involves rolling things and friction. Here's what you'll need to play:

• a big flat board that's at least 6 inches wide and 2 feet long

• a large thick book or a few smaller books totaling about 2" - 3"

• three cans of soup all the same exact size and brand. One should be a cream soup like cream of mushroom, one should be a clear soup like chicken broth and one should be a chunky soup like vegetable or chicken noodle.

Find yourself a big open room. You may have to move some furniture around. Lay your books down on the floor at one end of the room and rest one end of the board on top of it. The board should now look like a ramp.

The ground rules are as follows:

1. You must start all the cans from the exact spot on the top of the ramp and you're not allowed to roll them or push them in any way. The only thing that gets them going is gravity!

2. Before you try it out, study each can carefully. Then make a prediction about who the winner will be and write down your prediction.

3. In order to make sure your results are accurate, repeat the experiment at least three times.

Okay, here's the challenge question: Which do you think will roll farther down the ramp, the can of clear soup, the can of creamed soup or the can of chunky soup? (Maybe they'll all go the same distance, after all, they're the same size and shape!)

Related Web Sites

Friction Sites

Science Projects for All Students: Friction Activities
http://www.fsbassociates.com/sciprojects/friction.htm

General Science Sites

Science and Technology for Children Curriculum
http://www.si.edu/nsrc/pubs/stc/overv.htm

The Natural History Museum (London)
http://www.nhm.ac.uk/index.html

Edison National Historic Site
http://www.nps.gov/edis/

Endangered Species Program
http://endangered.fws.gov/

National Inventors Hall of Fame
http://www.invent.org/book/index.html

Understanding Our Planet Through Chemistry
http://minerals.cr.usgs.gov/gips/aii-home.htm

Maps and References
http://www.cgrer.uiowa.edu/servers/servers_references.html

Glossary of Terms

Potential Energy: Energy that can be used later. (When you're at the top of a hill, you have potential energy.)

Kinetic Energy: The energy of an object in motion. (Roll down the hill, and you've turned your potential energy into kinetic energy.)

Gravity: The force that pulls things toward the Earth.

Friction: When one thing slides against another, friction slows down the motion.

Drag: Friction between a moving object and the air around it. Drag also slows things down.

Momentum: The "oomph" of a moving object. The more momentum something has, the longer it can keep moving and the harder it is to stop.