Name: Motion on Rough Inclined Plane
Uploaded: 2019-07-19
Duration: 6 min 27 s
Description: You know that smoothness of the surface influences the friction on the object moves over it. Let us discuss the motion of a block on a rough surface in this...

Question

What is frictional force? What is it due to?

Accepted Answer

Whenever a body tends to move over the surface of another body, each body exerts a frictional force on the other which is parallel to the surfaces in contact. The frictional force on each body is opposite to the direction of its motion relative to others.

Thus, when a body moves from left to right on a horizontal table then frictional force acts towards left on body and towards right on table.

Consider a block at rest on a table as shown in fig. $1$ a. Two forces acting on the block are:

(i) Weight $m g$ of the block acting vertically downward.

(ii) Force of reaction $P$ acting on the block due to table which is directed vertically upwards and passes through centre of gravity of block. As the block is in equilibrium $P = m g$

When a small horizontal force $F$ is applied on the block and block does not move the $P$ , gets inclined to vertical as shown in fig.1b. $P, m g a n d F$ form a closed triangle as block is in equilibrium. The force $P$ can be resolved into (i) $P \cos θ$ which is perpendicular to surface and is equal to Normal reaction balances the weight $R = m g$

(ii) $P \sin θ$ is parallel to contact surfaces and is called force of static friction.

What friction is due to

Modern theory says that it is a result of the electromagnetic attraction between charged particle in two touching surfaces. Friction arises due to roughness of the two surfaces in contact.

What is frictional force? What is it due to?

Important Questions on Friction

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