Levers of the 1^st Order [Class I Levers]

In this type of lever the effort and the resistance (load) are situated on either side of the fulcrum.

Let us consider the lever AB which is used to overcome a load L at B by applying the effort E at A. The fulcrum of the lever is at F as shown in the figure below.

Levers of first order

The distance AF is called the effort arm and the distance BF is called the load arm.

If the lever is in equilibrium, then by applying the principle of moments about the fulcrum, we get

Clockwise moment = Anticlockwise moment

Effort x Effort arm = Load x Load arm

The ratio of the effort to the load is the mechanical advantage of the lever, therefore

Depending upon the relative position of load, fulcrum and effort, the mechanical advantage (shown in figure below) of the class I lever may be any of the following:

Relative positions of load, fulcrum and effort of class I lever

• M.A. = 1,

when Load arm = Effort arm, e.g. beam balance

• M.A. > 1,

when Effort arm > Load arm, e.g. Cutting pliers

• M.A. < 1,

when Effort arm < Load arm, e.g. Garden scissors

Equal Arms Beam Balance

A beam balance is an example of the class I type of levers (Shown figure below).

Beam Balance

It consists of two arms of equal lengths and two pans of equal weights. It works on the principle of moments. The turning effect produced by the mass on the left pan is equal to the turning effect produced by the pan on the right. Thus, if standardized weights are used in one of the pans the weight in the other pan can be known.

A true balance remains in equilibrium when either equal weights are put in both the pans or equal weights are removed from both the pans.