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.

 

 

 

Datasheets


N° of component