(a) Define frictional force (or friction)
(b) Explain why frictional force is said to be a contact force.
(c) Explain why magnetic force is said to be a non-contact force.
What can you comment on the objects in contact for them to experience frictional force?
Which of the following are non-contact forces?
Magnetic force, Frictional force, Gravitational force, Electrostatic force.