PULLEY

A pulley is a simple machine. It consists of a wheel mounted on an axis which is fixed to a frame called block. The wheel is free to rotate. With the help of pulley we can lift heavy loads very easily by applying little force and also change the direction of force.

FIXED PULLEY: -

If the block of the pulley is fixed to a strong beam or ceiling, the pulley will not move and is called a “Fixed Pulley”.

MECHANICAL ADVANTAGE OF FIXED PULLEY: -

In fixed pulley, the effort ‘P’ is applied which is equal to the load ‘W’, if we ignore weight of rope and force of friction between rope and pulley then:

effort = load

P = W

Dividing both sides by P

P/P = W/P W/P = 1 Since [W/P = M.A]

So therefore M.A = 1

This shows that fixed pulley can only change the direction of force but it will lift load equal to the effort applied on it.

MOVEABLE PULLEY: -

In a moveable pulley, one end of the rope which passes around the pulley is tied to a firm support ‘O’ and effort ‘P’ is applied to the other end. The load is hung from the hook of the block. As the load is applied by two segments of rope, the effort becomes twice of the applied value. i.e.

EFFORT = 2 x P

In equilibrium condition we have

Load = Effort

W = 2P

Dividing both sides by P

W/P = 2

But [W/P = M.A]

Thus

M.A. = 2

This shows that a moveable pulley can lift a load double the effort.