# Simple Machines - Compound Machines

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In many instances, the combination of two or more simple machines achieves results that cannot be achieved by a simple machine alone. Such combinations are known as compound machines. An example of a compound machine is the common garden hoe. The handle of the hoe is a lever, while the blade that cuts into the ground is a wedge. Machines with many simple machines combined with each other—such as typewriters, bicycles, and automobiles—are sometimes referred to as complex machines.

## Resources

### Books

Bains, Rae. Simple Machines. Mahwah, NJ: Troll Associates, 1985.

Macaulay, David. The New Way Things Work. Boston: Houghton Mifflin Company, 1998.

David E. Newton

## KEY TERMS

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Compound machine

—A machine consisting of two or more simple machines.

Effort force

—The force applied to a machine.

Friction

—A force caused by the movement of an object through liquid, gas, or against a second object that works to oppose the first object's movement.

—A mathematical measure of the amount by which a machine magnifies the force put into the machine.

Resistance force

—The force exerted by a machine.

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