Lever

From Wikinfo

Contents 1 Definition 2 Early Work 3 Force and Levers 3.1 An Example 3.2 Principle of the Lever 4 The Three Classes of Levers 4.1 Examples 4.2 Examples 4.3 Examples 4.3.1 References

Definition

A lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object. This is also termed mechanical advantage, and is one example of the principle of moments. The principle of leverage can also be derived using Newton's laws of motion and modern statics.

Early Work

The earliest remaining writings regarding levers are provided by Archimedes ("Give me a place to stand, and I can move the Earth.", a remark of Archimedes quoted by Pappus of Alexandria) who formally stated the correct mathematical principle of levers.

Force and Levers

The force applied (at end points of the lever) is proportional to the ratio of the length of the lever arm measured between the fulcrum and application point of the force applied at each end of the lever. (M=Fd)

An Example

Principle of the Lever

The principle of the lever tells us that the above is in static equilibrium with all forces balancing. The force applied upwards on the boulder is equal to the ratio of the lever arms times the force applied downward at the other end. (40/2)*50 = 1000. By slightly increasing the downward force the boulder begins to move.

The Three Classes of Levers

There are three classes of levers representing variations in the location of the fulcrum and the input and output forces.

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Class 1

File:Lever class1.png

Examples

1. Seesaw
2. Teeter-totter
3. Pliers

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Class 2

File:Lever class2.png

Examples

1. Wheelbarrow
2. Nutcracker

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Class 3

File:Lever class3.png

Examples

1. Human arm
2. Tongs

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See also: engineering mechanics

References

• Adapted from the Wikipedia article, "Lever" http://en.wikipedia.org/wiki/Lever, used under the GNU Free Documentation License