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Name: John N.
Status: student
Age: 13
Location: N/A 
Country: N/A
Date: 10/24/2004

Does friction increase as temperatures change

Generally yes. If you slide two surfaces together, the resisting force is called friction. The amount of friction depends on many things. Perhaps most important is the type of material and the condition of the surface. Also, the presence of liquids or solids in between the surfaces.

For example, oil between two steel surfaces makes the friction low. Dry bare steel (no oil) sliding against another piece of steel gives higher friction. Hot steel surfaces tend to oxidize in air. The oxide has high friction.

The friction coefficient is one way of measuring friction and is the sliding force divided by the load force. For example, if a 20 pound brick needs 5 pounds to make it slide, the friction is 5/20 = 0.25. Bare steel is 0.7. Engine bearings might be 0.08. Some plastics, like DuPont's Teflon (TM), have fairly low friction. Of course, they are not very strong.

Oil and grease are used to lubricate bearings in cars, machines, etc. At very low temperature, the oil and grease are thick, and the bearing has high friction. The friction decreases as the temperature increases. At very high temperature the friction may increase because the oil and grease do not lubricate very well any more.

Friction also depends on the amount of load or force. For example, sliding plastic, metal or ice with a gentle pressure will give a certain friction coefficient. The same materials can give a different friction coefficient if the load is increased to tons.

Bob Erck

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