Question

What is the order of coefficient of static friction between tyre and road in dry condition?

A. >1
B. <1
C. =1
D. <.5

Answer 1

Hint: When an object is in contact with the smooth surface the contact force acting on it will be normal force only. When the object is in contact with a rough surface then the contact forces acting are normal force and friction force. Based on surface conditions also frictional force varies.

Complete answer:
Basically there are 4 fundamental forces in nature. Hence whatever the force we talk about, that must be derivative of one of these 4 fundamental forces. Now the friction force is a type of contact force which arises due to interlocking between the surface and the object. It comes under the category of electromagnetic fundamental force which arises due to interaction between the atoms of contact surface and the resting base of the object.
We usually see that on wet surfaces when vehicles apply brakes they get skidded. Even though there will be many reasons for that skidding, the main reason is the friction between the vehicle tyres and contact surface.
Hence on wet surface friction will be very less. But if the surface is too wet then friction might be more. Take an example of white marble. If the surface of white marble is too wet and if we place another white marble on it, it will be sometimes difficult to separate them or rub one on another due to friction.
But the dry surfaces have more friction. Usually the maximum value of coefficient of friction is 1 and reaching one is rare. Since dry surfaces have more friction its coefficient will be near to one i.e slightly less than one.

So, the correct answer is “Option B”.

Note:
There are some materials whose coefficient of friction is greater than one. One of the examples is silicon rubber. Theoretically that means the amount of friction force required to move is greater than the normal force as the friction is produced by normal force and friction coefficient.