Let m = Mass of reciprocating parts,

l = Length of connecting rod PC,

r = Radious of the crank OC,

Θ = Angle of inclination of the crank with the line of stroke PO,

ω = Angular speed of the crank,

η = Ratio of length of the connecting rod to the crank radious = l/r

We have already discussed in previous articles that the acceleration of the reciprocating parts is approximatey given by expression,

Inertia force due to reciprocating parts or force required to accelerate the reciprocating parts,

Inertia force due to reciprocating parts or force required to accelerate the reciprocating parts,

We have discussed in the previous article that the horizantal component of the force exerted on the crank shaft bearing (i.e F

_{BH}) is equal and opposite to inertia force (F1). This force is an unbalanced one and is denoted by F_{U }.
Unbalanced force

The expression (m.ω^2 .r cos Θ) is known as Primary unbalnced force and (m.ω^2 .r [cos 2Θ]/n ) is called secondary unbalanced forces.

The expression (m.ω^2 .r cos Θ) is known as Primary unbalnced force and (m.ω^2 .r [cos 2Θ]/n ) is called secondary unbalanced forces.