Mar 282013

A machine is a device that is capable of converting the available forms of energy to useful work.

Each part of a machine, that undergoes relative motion with respect to some other part, is called kinematic link (or kinematic element). Kinematic links help in the transmission of motion, from one machine part to another.

The connecting rods shown in the image below (brown in colour) are individual kinematic links. They are used for transmitting motion from piston to crankshaft in an engine.

Connecting Rods

Kinematic links form the backbone of any mechanical system.

Types of Kinematic links:

Based on rigidity, kinematic links can be broadly classified into three types. They are:

  1. Rigid link
  2. Flexible link and
  3. Fluid link

A kinematic link need not be essentially rigid. It must be resistant enough to transmit motion.

1. Rigid Link:

Rigid links are those kinematic links that do not undergo any change of shape when transmitting motion (or when subjected to external forces). In reality, no rigid links exist. However, kinematic links whose deformation is very small are considered as rigid links. Some good examples of rigid links are crankshafts, connecting rods (pictured above) and cam followers. These links do not undergo significant deformation while transmitting motion.

Flexible link:

A flexible link is a resistant kinematic link that undergoes partial deformation when transmitting motion. Its deformation does not hinder its effectiveness of transmission. Some examples of flexible links are belts (in belt drives) and chains (in chain drives).

The belt found in the following image is a flexible link.

Belt - Flexible Link

Fluid Link:

A fluid link makes use of a fluid (liquid or gas) to transmit motion, by means of pressure. Fluid links always undergo deformation when transmitting motion. Some good examples where fluid links are used are pneumatic punching presses, hydraulic jacks and hydraulic brakes.

Kinematic pair is a combination of two kinematic links. It is discussed in detail in this article.

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I am a mechanical engineer with a passion for technical stuff. I am the founder and former editor-in-chief of

  • manib4u

    really got some stuff

    • Surjeet S

      Thanks :)

  • leela kishore

    what is the difference between belt drive and rope drive? how can we justify what to use?

    • Surjeet S

      Both belt and rope drives are used for transmission of power between two shafts. In general, when a small power is to be transmitted over a short distance (say less than 8m), belt drives are used. When a large amount of power is to be transmitted over a long distance (say upto 150m), rope drives are used.

      • bhima leelakishore

        what about transmitting more power to a small distance(say 2 to 4) meters? which drive has to be used?

        • Surjeet S

          For transmitting huge amount of power over a very small distance, we use gear drives. Chain drives and V-belt drives can also be used for transmitting relatively large power over a short distance (say 1-4m).

  • bhima leelakishore

    what is difference between ordinary belt and v-belt. What is the property that makes v-belt to transmit more power.

  • umakant yadav

    fluid link changes the form of energy to be transmitted ?


    But what deformation u r talking about, in size, or shape or anything else, zara ache se batao na

  • gollavilli hari

    tis .com is not fully developed.but upto mark it is excellent.