Lever

In physics, a lever (from Old French levier, the agent noun to lever "to raise", c. f. levant) 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 studies

The earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. Give me the place to stand, and I shall move the earth is a remark of Archimedes who formally stated the correct mathematical principle of levers (quoted by Pappus of Alexandria).

In ancient Egypt, constructors used the lever to move and uplift obelisks weighting more than 100 tons.

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. Mathematically, this is expressed by M = Fd.

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.

First-class levers

Examples:

1. Seesaw (also known as a teeter-totter)
2. Crowbar
3. Pliers (double lever)
4. Scissors (double lever)

Second-class levers

Examples:

1. Wheelbarrow
2. Nutcracker (double lever)
3. The handle of a pair of nail clippers

Third-class levers

Examples:

1. Human arm
2. Tongs (double lever) (where hinged at one end, the style with a central pivot is first-class)
3. Catapult
4. Any number of tools, such as a hoe or scythe
5. The main body of a pair of nail clippers, in which the handle exerts the incoming force

See also

• Engineering mechanics
• Voting lever
• Linkage (mechanical)