Lever

 Definition

          In physics, a lever (from French lever, "to raise", c.f. a levant) is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force (effort) that can be applied to another object (load). This leverage is also termed mechanical advantage, and is one example of the principle of moments. A lever is one of the six simple machines.

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 (pivoting point) and application point of the force applied at each end of the lever.

                   Mathematically, this is expressed by M = Fd, where F is the force, d is the distance between the force and the fulcrum, and M is the turning force known as the moment or torque.

Classes

Class 1: The fulcrum is located between the applied force and the load, for example, a crowbar or a pair of scissors or a seesaw

A class-1 lever has the fulcrum located somewhere between the effort and the load. With this kind of lever, the direction of force is changes. Effort applied downward moves the load up. Effort applied upward moves the load down.

 

Class 2: The load is situated between the fulcrum and the force, for example, a wheelbarrow or a nutcracker.

A class-2 lever has its fulcrum at one end of a lever arm. The load is between the fulcrum and the effort. With this kind of lever, the direction of effort is not changed. Pushing up on the class-2 lever arm pushes up on the load. Pushing down on the lever arm pushes down on the load. To gain a mechanical advantage, the load is places closer to the fulcrum than to the effort. The class-2 lever always reduces effort.

 

Class 3: The force is applied between the fulcrum and the load, for example, a tweezers or human mandible

In a class-3 lever, the fulcrum is at one end, and the effort is applied between the fulcrum and the load. With this kind of lever, the direction of effort is not changed. The load moves in the same direction as the effort. The gain offered by a class-3 lever is one of distance.