Friction at negative value?

Question

at what situation can we say that the value of a friction is negative? sorry for the bad grammar :)

Answer 1

i don't know whether i misunderstand you.

but wasn't friction always get negative because it is the opposition of the applied force. (there is only friction when there is an applied force)

Answer 2

i am fairly sure you cant get a 'negative' friction value as such, wouldn't that mean things speed up when sliding across them?

Answer 3

friction can never have a negative value. friction force is the force that opposes the motion of the particle or an object.it is in the direction opposite to the direction of motion of objects.considering your idea hypothetically for friction being negative,then it acts as a driving force for the motion of body instead of a resisting force,but that is impossible.so your question or an assumption of friction being negative is wrong..

Answer 4

Whatever sign convention you want to use for friction, that sign is never changing. It always opposes motion.