Can friction act in the direction of motion?

Question

If yes, give an example and if not, explain why not.

Now, given that this is a question as a HW assignment, I would say no because for one object to move one way, it is done by friction on the opposite direction.

HOwever, my friend argues that the direction of friction would be the same as the surface that the object was on. Thus, the table and friction are in the same direction.

I argued that friction force of one object cant be applied to another object....

Can anyone resolve this issue?

done by overcoming friction*

well, newtons third law would say force of 1 on 2 is same as force of 2 on 1. Thus, the surface of which the object is moving goes the opposite way...the only reason the table doesnt move is it has friction force to the floor.

My friend was comparing the friction force of the object to the direction the table was travelling in.

Answer 1

The force of friction acts in the direction to oppose motion.

Think, conceptually, what it would mean if friction did/could act in the same direction as motion....
If an object is sliding along a floor without anything acting on it besides friction, it would continue to accelerate for no reason, its velocity every increasing, and thus continually gaining kinetic energy. Where does this energy come from?
On the other hand, if the force of friction acts to oppose motion then the object will continually slow and loose energy in the form of heat.

This statement confuses me,
"Thus, the table and friction are in the same direction. "
--Just what direction is the table in?
I can understand the concept of friction acting in a certain direction since it is vector, but a table?


EDIT:
OK, I see what you were saying now.

I think the distinction which needs to be made here is on which object the force is acting on.

Take this hypothetical example.....

A block sliding on a table which is sitting on a frictionless floor. The mass of the block is m, the mass of the table is M. The coefficient of friction between the block and the table is mu, and the coefficient of friction between the table and the floor = 0 (frictionless).
The force of friction between the block and the table which act on the block is given as F_f = m*g*mu.
Due to Newton's 3rd Law we know that this must also equal the magnitude of the frictional force acting on the table....but in the opposite direction.

We now have two objects, each of which have a net force acting on them.
The block has the force of friction acting on it in the "negative" direction and the table has a frictional force acting on it in the "positive" direction.
In both cases the frictional force acting on the particular object in question is acting in the direction to oppose motion of that object. Relative to the other object....the forces want to bring both objects to a stop relative to the other object.
It is irrelevant that both or neither of these objects might be at rest with respect to the frictionless floor or the observer, they would like to be at rest with respect to each other, the relative motion between the two being zero.

Answer 2

Direction Of Frictional Force

Answer 3

It's impossible, because of the law of conservation of energy.

Imagine an object on a surface where friction pushed in the direction of motion. If you pushed the object a little bit, the friction would keep pushing it faster in the same direction, and the object would keep moving forever, faster and faster. Obviously that's impossible.

Friction is always opposed to the direction of motion.

Answer 4

when you have rotational motion in the same direction as the linear motion then force of friction is in the same direction as motion