Mechanical Basics

Theory of Machines

What is Theory of Machines?

        Theory of Machines simply called TOM is another important subject in Mechanical Engineering; it deals with the motions and their responsible forces of a body. In the theory of machines, we are going to study different types of Machine Elements, Laws, Components, Transmitters, Balancing of automobiles, etc. It is the combination of the topics Kinematics and Dynamics of Machines. 

For example, let us consider the shaping machine (you can read about the shaper machine very soon on this website). A shaper is a machine tool used to cut, groove the materials using cutting tools whereas “cutting material will stay still without any motion (fixed) and the cutting tool will be moved to and fro directions“.

Theory of Machines


     Internal Mechanism of a Shaper

      So, the movement of to and fro is achieved with the help of the internal mechanism which is to convert the rotary motion (developed by the motor) into the reciprocating motion. So such conversion is possible only when we are aware of the links, kinematics, devices, and parts that are responsible for the conversion of motions (like gears, gear trains), etc. So, the Theory of Machines is the key subject for such learning.

What we can learn on this page?

  1. Theory of Machines Syllabus.
  2. Theory of Machines Basics.
  3. Theory of Machines Textbook. (for reference)

Theory of Machines Syllabus:

The syllabus is the particulars we read or learn in our semester or academics. As the syllabus will vary according to their University, so I listed out the important syllabus that everyone will follow, and this syllabus is equal to GATE (Graduate Aptitude Test in Engineering).

  • Mechanisms
  • Kinematics and Dynamics Analysis of Planar Mechanisms.
  • Governors.
  • Balancing.
  • Gears.
  • Gear Trains.
  • Vibrations.

Theory of Machines Basics:


It is the element in a machine that forms a joint.


It is the combination of the two links

Kinematic Pair: 

It is the relative motion between the pairs is said to be constrained, then it is called the Kinematic Pair.

There are different types of Kinematic Pairs. They are classified as

  • According to Type of Motion Kinematics are Sliding Pair, Turning Pair, Rolling Pair, Screw Pair, and Spherical Pair
  • According to Type of Contact Kinematics are Lower Pair and Higher Pair.
  • According to Type of Closure Kinematics are Self Closed Pair and Force-Closed Pair

Kinematic Chain:

It is the combination of the Kinematic Pairs, and the relative motion between them should be completely constrained.

Example: Crankshaft with bearings, Connecting rod with a crank, etc.


It is defined as the method of obtaining different types of mechanisms by fixing the links ends.

Types of Kinematic Chains:

  • Single Slider Crank Chain: 

The Inversion of this type of chain is Pendulum pump or Bull Engine, Whitworth quick return motion, Rotary internal combustion engine or Gnome engine, Crank & Slotted lever quick return mechanism and Oscillating Cylinder engine.

  • Four Bar or Quadric Cycle Chain:

The Inversion of this type of chain is the Crank and Lever mechanism, Double crank, or Coupling rod of Locomotive and Watt’s indicator mechanism.

  • Double Slider Crank chain:

The Inversion of this type of chain is Elliptical Trammels, Scotch yoke mechanism, and Oldham‘s Coupling comes under this Kinematic chain.


If a link is fixed at one end and the other links in the Kinematic Chain can Transform or Transmit the motion, such a process is called the Mechanism.

Instantaneous Centre:

It is defined as the center which will be changed from one instant to another. The line which is drawn through an Instantaneous center and perpendicular to the plane of motion is called the Instantaneous axis.

Hooke’s Joint: 

It is the joint that is used to connect two shafts at a small angle. It is also called the Universal Joint. We can see those joints frequently in connecting the Propeller shaft of an Automobile.

Theory of Machines Textbook (for reference):

Student needs to refer the textbooks to grab the knowledge that not even found in the classroom teaching. When the student starts referring to the textbooks then the seed of knowledge will start growing in oneself. So, do not stick to the classroom notes but also try to refer to the textbooks that increase the knowledge.

Here I am mentioning a few Theory of Machines book for your references, please go through them.

  • Theory of Machines by S S Ratan.
  • Theory of Machines by Thomas Bevan.
  • Theory of Machines by R S Khurmi & J K Gupta.
  • Theory of Machines by Dr. R K Bansal.

Note: Please refer to the syllabus in each textbook before you refer or purchase.