LEVER

Lever is a simple machine which is used to lift heavy bodies or heavy load in a very easy way.

Lever consists of a rigid bar capable to rotate about a fixed axis called fulcrum. Effort is applied at one end of the bar and weight can be lifted from the other end.

TYPES OF LEVER: -

There are three kinds of lever depending upon the positions of load, effort and fulcrum.

FIRST KIND OF LEVER: -

In the first kind of lever, the fulcrum F lies between effort (P) and load (W).

Example: common balance, seesaw, scissors, handles of hand pump.

SECOND KIND OF LEVER: -

In the second kind of lever, load (W) lies between effort (P) and fulcrum (F).

Example: door, nutcracker, punching machine.

THIRD KIND OF LEVER: -

In the third kind of lever, effort (P) lies between load (W) and fulcrum (F).

Example: forceps, jaws, human forearm, fire tong.

MECHANICAL ADVANTAGE OF LEVER: -

Consider the example of a lever of 1st kind.

In equilibrium position torque of effort is always equal to the torque of load. i.e.

Clockwise torque = Anti clockwise torque

Torque of effort = torque of load

OR

effort x effort arm = weight x weight arm

P x OA = W x OB

OA = W x OB/P

W/P = OA/OB

But [W/P = M.A.]

M.A = OA/OB

OR

M.A. = Effort arm / weight arm

This equation shows that mechanical advantage of lever can be increased: ·         By increasing effort arm. ·         By decreasing weight arm