# HIGHLIGHTS THEORY OF MACHINES

THEORY OF MACHINES: HIGHLIGHTS

Lower pairs have line contact. Higher pairs have point contact or sliding contact. Rolling pairs have surface contact. Link is a resistant body which has relative motion but does not affect motion of other members (pendulum has one degree of freedom as θ).Piston and piston rod form one link since there is no relative motion between these.

Kinematic pair—–Combination of two links such that the motion is constrained.

There are different types of kinematic pairs depending on the following considerations:

•  relative motion
•  type of connection between the links
• On the basis of how the links are held together (closed or open pair)

DEGREES OF FREEDOM

Degrees of freedom mean freedom in motion i.e. number of independent co-ordinates to define the motion completely.

For example: A nut having rotary as well as translator motion over a bolt has only one degree of freedom since bolt and nut do not have any  connection between them. A rigid body has 6 degrees of freedom (3 motions of translation and 3 motions of rotation).A flexible body has infinite degrees of freedom. A link has three degrees of freedom. Fully constrained body has one degree of freedom. An unconstrained body has degrees of freedom more than one. A body can be constrained only by the application of a force.