The links in a mechanism are mostly connected by means of pin joints. The rubbing velocity is defined as **the algebraic sum between the angular velocities of the two links which are** **connected by pin joints, multiplied by the radius of the pin.**

Consider two links *OA* and *OB* connected by a pin joint at *O* as shown in Fig. Let

ω1 = Angular velocity of the link *OA* or the angular velocity of the point *A* with respect to O

ω2 = Angular velocity of the link *OB* or the angular velocity of the point *B* with respect to *O*, and *r *= Radius of the pin.

According to the definition,

Rubbing velocity at the pin joint *O* is given by the formula

=(ω1-ω2)*r , if the links move in the same direction

= (ω1+ω2)*r, if the links move in the opposite direction where ω_{1} = angular velocity of link 1

ω_{2} = angular velocity of link 2 r = radius of the pin

**Note : **When the pin connects one sliding member and the other turning member, the angularvelocity of the sliding member is zero. In such cases,

Rubbing velocity at the pin joint = ω*r*

where ω=Angular velocity of the turning member, and *r *= Radius of the pin.

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