Frictional Loss in Lifting Machine and Law of Machine

Frictional loss is the part of the inputs or work done by the effort used to overcome the friction of the machine. No machine can be 100% frictionless; therefore, some parts of the inputs are always used to overcome the friction of the machine. Thus, the efficiency of the real machine always lies below 100%.

 

Frictional loss = Input – Output

 

The relationship between the load and effort is shown in the graph in Figure 13.2.

Figure 13.2 Relationship Between Load and Effort (Law of Machine)

OA – Effort required overcoming the friction.

where P_i is the ideal effort required to raise a given load, P_a is actual effort required to raise the load, and P_f is effort required to overcome the friction.

For an ideal machine, η = 1

Putting the value of P_i in Eq. (13.1).

The relation between load and effort is given by an equation, P = m·W + C which is known as law of machine. Where m is slope of the line and equal to  and C is constant known as frictional constant.