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# Uses of Friction

by Ron Kurtus (revised 21 May 2009)

Although you normally hear about trying to reduce or eliminate friction, it actually has some important uses.

Since friction is a resistance force that slows down or prevents motion, it is necessary in many applications to prevent slipping or sliding. In those cases, there is an advantage of having friction. However, too much friction can be a nuisance, because it can hinder motion and cause the need for expending extra energy. A good compromise is necessary to get just enough friction.

Questions you may have include:

• What are important uses of friction?
• How is friction a nuisance?
• What is a good compromise for using friction?

This lesson will answer those questions. Useful tool: Units Conversion

## Important uses

In some situations, friction is very important and beneficial. There are many things that you could not do without the force of friction.

### Walking

You could not walk without the friction between your shoes and the ground. As you try to step forward, you push your foot backward. Friction holds your shoe to the ground, allowing you to walk. Consider how difficult it is to walk on slippery ice, where there is little friction.

Bear did not heed warning sign

### Writing

Writing with a pencil requires friction. You could not hold a pencil in your hand without friction. It would slip out when you tried to hold it to write. The graphite pencil led would not make a mark on the paper without friction.

A pencil eraser uses friction to rub off mistakes written in pencil lead. Rubbing the eraser on the lead wears out the eraser due to friction, while the particles worn off gather up the pencil lead from the paper.

### Driving car

Your car would not start moving if it wasn't for the friction of the tires against the street. With no friction, the tires would just spin. Likewise, you could not stop without the friction of the brakes and the tires.

## Problems from friction

Friction can cause problems or be a nuisance that you try to minimize.

### Makes movement difficult

Any time you want to move an object, friction can make the job more difficult. Excess friction can make it difficult to slide a box across the floor, ride a bicycle or walk through deep snow.

An automobile would not move forward very well unless its friction was not reduced. Oil is needed to lubricate the engine and allow its parts to move easily. Oil and ball bearings are also used in the wheels, so they will turn with little friction.

### Wastes energy

In any type of vehicle—such as a car, boat or airplane—excess friction means that extra fuel must be used to power the vehicle. In other words, fuel or energy is being wasted because of the friction.

Fluid friction or air resistance can greatly reduce the gas mileage in an automobile. Cars are streamlined to reduce friction. However, driving at highway speeds with your windows open can create enough drag on the car to greatly lower your gas mileage.

### Heats parts

The Law of Conservation of Energy states that the amount of energy remains constant. Thus, the energy that is "lost" to friction in trying to move an object is really turned to heat energy. The friction of parts rubbing together creates heat.

You've seen how people will try to start a fire by vigorously rubbing two sticks together. Or perhaps you've seen an automobile spin its wheels so much that the tires start to smoke. These are examples of friction creating heat energy. Just rub your hands together to create the same effect.

Besides the problem of losing energy to heat, there is also the threat of a part overheating due to friction. This can cause damage to a machine.

### Wears things out

Any device that has moving parts can wear out rapidly due to friction. Lubrication is used not only to allow parts to move easier but also to prevent them from wearing out. Some other examples of materials wearing out due to friction include the soles of your shoes and a pencil eraser.

## Compromise

A compromise is needed between too much friction and not enough.

### Reducing friction

Consider the situation where you wanted to slide a heavy box across the floor. You would want to reduce the friction between the box and the floor, so that it would be easy to move. Lubrication is often a way to reduce friction. There are also sliders or rollers that can be used to reduce the friction.

### Need for friction

But you would also want to increase the friction of your shoes on the floor, so that you would be able to get good traction and be able to push effectively. Soles made of rubber material that include treads can reduce slipping when walking, running or pushing a heavy object.

## Summary

Friction is necessary in many applications to prevent slipping or sliding. But also, it can be a nuisance because it can hinder motion. A good compromise is necessary to get just enough friction or a proper combination of frictions.

Observe little things around you

## Resources and references

Ron Kurtus' Credentials

### Websites

Friction Concepts - HyperPhysics

Friction - Wolfram Research Science World

Friction Resources - Extensive list

### Books

The following books are available from Amazon.com.

#### Basic

Complete Idiot's Guide To Physics by Johnnie T. Dennis; Alpha (2003) \$18.95

What Is Friction? (Ages 4-8) by Lisa Trumbauer; Children's Press (CT) (2004) \$4.95

Friction Science and Technology (Mechanical Engineering Series) by Peter J. Blau; Marcel Dekker Pub. (1995) \$89.95

Physics of Sliding Friction (NATO Science Series E:) by B.N. Persson, E. Tosatti; Springer Pub. (1996) \$358.00

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.

## Students and researchers

www.school-for-champions.com/science/friction_uses.htm

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