Question

a block of mass 10 kg is placed on a surface, what will be the frictional force experienced by it?

Answer 1

As no external force is acted upon the body so the frictional force acting on the body is zero.

Answer 2

Frictional force experienced will be zero.

But why ?

• First of all, when the block of mass 10 kg is placed on the surface, the mass is stationary. Hence, it should experience STATIC FRICTION.

• The maximum static friction that can be experienced by the block will be equal to $f=\mu_{s}\times mg$ , where $\mu_{s}$ is the static friction coefficient.

However, this static friction starts to act only well an external force is applied with an intention to push the block.

• When an external force starts pushing, the static friction also keeps on adjusting itself to stop the motion until a point when the box starts moving. After that kinetic friction starts to act.

Since there is no external force, the net friction experienced will also be zero.