Select all of the following statements that are true regarding
friction.
a.
The equations that relate friction to the normal force and the
coefficient of friction are vector equations.
b.
For an object at rest, if there is no lateral force attempting
to make the object slide over the surface on which it rests, then
there is no static friction force on the object.
c.
Friction is due to the electromagnetic force.
d.
Friction always opposes the motion of an object.