Question

Which of these is a contact force ?
A.Friction
B.Muscular force
C.Magnetic force
D. Both A and B are correct

Answer 1

Hint: Contact force is that force which acts on a body by coming in direct physical contact with it while non-contact forces are those which act from a distance and there is no need for physical contact for the force to act on a body.

Complete answer:
The forces in nature can be categorized on the basis of the fact that whether they act on the body by coming in physical contact with the body or not. On the basis of this, we have contact forces and non-contact forces.
Contact forces are those forces which can act on a body only by coming in direct contact with it. Non-contact forces are those forces which do not need to come in contact with the body and act in the body from a distance.
Friction is a contact force because it originates when two bodies slide over one another.
Muscular force is also a contact force as muscles need to come in direct contact with an object to apply the force.
Magnetic force is not a contact force because two magnets can attract each other from a distance without coming in contact with each other.

Therefore, the correct answer is option D.

Note:
There four fundamental forces of nature: Gravitational force, electromagnetic force, weak and strong nuclear forces; are all non-contact forces. The non-contact forces can be explained by the standard model of particle physics which says that these forces occur by interchange of certain mediating particles between two bodies.