The difference is the relative position of the fulcrum, load, and effort. In a first-class lever the fulcrum is between the effort and load; in a second-class lever the load is in the middle; and in a third-class lever the effort is in the middle.
A lever is a rigid component that rotates around a fixed pivot called the fulcrum. The effort is the input force applied to the lever, while the load is the output force or resistance being moved.
| Lever class | Arrangement and effect | Example |
|---|---|---|
| First class | Effort, fulcrum, load. The output force reverses direction. Mechanical advantage may be greater than, equal to, or less than 1. | Scissors, pliers, seesaw |
| Second class | Fulcrum, load, effort. The effort arm is longer than the load arm, so the ideal mechanical advantage is greater than 1. | Wheelbarrow, nutcracker |
| Third class | Fulcrum, effort, load. The effort arm is shorter than the load arm, so the ideal mechanical advantage is less than 1. | Tweezers, human forearm |
The turning effect of a force is its moment, calculated using: