Question

what is frictional force​

Answer 1

Answer:

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact.

Answer 2

In reality, all surfaces are not smooth but rough also and that's why exert some force on the body in the opposite direction of the motion to make the motion slow.

So, the roughness of the Surface is Friction and the force due to friction is the frictional force.