Kinematics: Higher and Lower pair types, also difference between Chain & Mechanism

Kinematic Pairs -- types:

A Kinematic pair comprising two contagious (ability to transmit) links are classified into two categories: 

• Lower Pair: These are kinematic pairs having sliding joints which are in surface to surface contact e.g. shaft & bush
• Higher Pair: These are kinematic pairs having either linear contact e.g. cam & follower OR are in point contact e.g. pivot on a plate

In the above Fig. two different types of joints have been shown and the third one is the combination of the first two. The symbol representing these three are also shown below each.

Some more basics of Kinematics are depicted in the Fig. below along with the description:

Degree of Freedom of a mechanism:

One of the important concepts of Kinematics is to define the degree of freedom of the mechanism.It is defined by Grubler's Equation, which can be written as follow;

F = 3(n-1) - 2g

Where, F is the degree of Freedom, 'n' is the number of links (including the fixed link), 'g' represents the number of joints. We may say 'F' is a function of 'n' and g''. 

Capability of rotation in  Four-Bar Linkages:

In a four-bar linkage only the shortest link has the capability to rotate, as per Grashof's rule. The only exception being a double crank and double rocker mechanism.