Newton’s Laws of motion are very important from the perspective of IIT JEE Physics preparation. This IIT study material discusses a few concepts related to friction.

The first thing to be discussed in the IIT JEE video lecture is the method to find the direction of the force of friction. Force of friction opposes the relative motion between the surfaces. The direction of the frictional force has been with the help of a diagram.

Another diagrammatic illustration has been taken in the JEE online lecture to explain the concept. Here an object is placed on top of another one, and the one on the bottom is pulled. If there is no friction (no horizontal force component), then the object on the top would fall backwards.

An example of a bicycle which is very important for understanding this topic has been discussed in this online IIT JEE coaching lecture. It is assumed that there is no frictional force. In such a case the cycle would have no forward motion, because the rear tire would not show a forward motion. Friction is responsible for the forward motion practically.

In case there is no friction between the ground and the front tire, the front tire would not rotate. Skidding would occur in such case. The torque for rotation of the front tire is provided by friction in practical situation. This is the explanation for skidding of bikes on mud or other wet surfaces. This concept is very important and problems related to this can be often seen in previous years IIT JEE papers and JEE solutions.

Another example is taken in the online IIT JEE coaching lecture. Here a spherical/cylindrical object is assumed to be rolling on a surface that is first flat, and then inclined. The object would roll from the flat surface onto the incline. In this case there is both linear and rotational motion. Once again the condition of no friction is assumed.

After it climbs the incline, then its linear velocity would decrease (due to gravity), whereas the angular velocity would remain unaltered (there is no friction).

Also, if a spherical object is left on the top of an incline and there is no friction, the sphere would come down without exhibiting a rotational motion.

Numerous examples related to this topic can be seen illustrated in IIT preparation books. Thus you can understand this even more clearly using IIT books or other conceptual IIT JEE video lectures available here.


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