Law of a Machine:
The term ‘law of a machine may be defined as the relationship between the effort applied and the load lifted. Thus for any machine, if we record the various efforts required to raise the corresponding loads and plot a graph between effort and load. We shall get a straight line AB as shown below figure:
We also know that the intercept (OA) represents the amount of friction offered by the machine. In other words, this is the effort required by the machine to overcome the friction, before it can lift any load.
Mathematically, the law of a lifting machine is given by the relation:
P = mW + C
P = Effort applied to lift the load
m = A constant is called the coefficient of friction which is equal to the slope of the line AB.
W = Load lifted
C = Another constant which represents mechanical friction.