Figure 2 shows the ways the block and tackle are used.

The mechanical advantage depends on the use:

## Force (disregarding bearing friction and rope rigidity) :

**Formula **

a) Fixed Sheave or pulley

## F1 = Fo

b) Free sheave or pulley

## F1 = Fo/2

c) Ordinary pulley block

## F1 - Fo/n

d) Differential pulley block

## F1 = 1/2(1 - d/D)Fo

e) Multiple Differential Pulley Block

## F1 = Fo/2n

**Where: **

F1 - Force required to raise ot lower the load

Fo - Load

n = number of pulleys

d, D - Diameter of the pulleys

## Path of the Load

** Formulas - (figure 3) **

a) Fixed sheave

## s = h

b) Free sheave

## s = 2 x h

c) Ordinary pulley block

## s = n x h

d) Differential pulley block

## s = 2h/(1-d/D)

e) Multiple differential pulley block

## h = D/2n

## Moment of Force

Moment M of a force F about a point O is te perpendicular distance from point O to the line of action of force F times the force F.

** Formula **

## M = F x d

**Where: **

M is the moment

F is the force

d is the distance

Resultant forces: (figure 5)

**Formula **

F1 x d1 + F2 x d2 + F3 x d3 + ..... Fn x dn = 0

Pbs: F may be positive or negative according the direction defined by clockwise or counterclockwise.