In physics, 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 studies
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. 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:
- Seesaw (also known as a teeter-totter)
- Crowbar
- Pliers (double lever)
- Scissors (double lever)
Second-class levers
Examples:
- Wheelbarrow
- Nutcracker (double lever)
- The handle of a pair of nail clippers
Third-class levers
Examples:
- Human arm
- Tongs (double lever ) (where hinged at one end, the style with a central pivot is first-class)
- Catapult
- Any number of tools, such as a hoe or scythe
- The main body of a pair of nail clippers, in which the handle exerts the incoming force
See also