2. The two links OA and OB are connected by a pin joint at O. If the link OA turns with angular velocity ?1 rad/s in the clockwise direction and the link OB turns with angular velocity ?2 rad/s in the clockwise direction, then the rubbing velocity at the pin joint O is (where r = Radius of the pin at O)
9. When the two elements of a pair have a surface contact when relative motion takes place and the surface of one element slides over the surface of the other, the pair formed is known as a