Law of coulomb friction, Mechanical Engineering

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Law of coulomb friction:

Coulomb in the year 1781 presented certain conclusions which are called as Coulomb's law of friction. These observations are based on experiments on block tending to move on the flat surface without rotation. These laws are appropriate at condition of impending slippage or once the slippage has begun. The laws are enunciated below:

1. The total force of friction, which can be developed, is not dependent on area of contact.

2. For low relative velocities between the sliding bodies, the total amount of frictional force is not dependent on velocity. But force required to start the motion is greater than that needed to maintain the motion.

3. The total frictional force, which can be developed is proportional to the normal reaction of surface of contact.

So, coefficient of friction (µ) can be defined as the ratio of the   limiting force of friction (F) to normal reaction (R) between the two bodies.


µ = Limiting force of friction/ Normal reaction = F/R

or, F = µ.R, In general µ < 1

The factor affecting coefficient of friction are:

1. The material of meeting bodies.

2. The roughness or smoothness of the meeting bodies.

3. The   temperature of environment.

Efforts to minimize it:

1. The use of proper lubrication can minimize friction.

2. Proper polishing of the surface minimizes it.


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