Friction and Acceleration

[Primarygun]

Imagine there is an object on the surface.

The surface is uniform smooth(with same friction over the all surface and friction is greater than 0).

Let's define the friction be f.

Act a f force to horizontally to the object continuously, it is continuous added.

It is obviously stationary.

I'm quite confused of here then. If there is 1N force pushed to it in the same direction to the f force added by hand.

What will be observed?

a.Move with acceleration first, then remains the velocity later on.

b.1.If f>kinetic friction, then the object accelerates first then decelerates to stop.

b.2. If f> kinetic friction, then the object will accelerates continuously forward.

Which one is correct?

[cyeokpeng]

QUESTION:

 

Is it possible to add the friction force on the object by hand? Friction force is characteristics of the system in equilibrium i.e the static force of friction is responsible in keeping the object from moving.

And static force of friction will always be acting opposite in direction to the direction of tending motion.

The other type of friction, which is the friction force acting on the object when the object is on the move, is the kinetic force of friction, which is also acting opposite in direction to the motion direction.

 

So question is, is it even possible to add the static force of friction by hand, that is in the case of your question? You may argue that by somehow increasing the roughness of the surface evenly throughout the surface, i.e the increase of roughness follows a uniform distribution. BUT NOTE THAT THE STATIC FORCE OF FRICTION IS ALWAYS ACTING IN THE OPPOSITE DIRECTION TO THE INTENDED MOTION.

So in your question, let's say we can somehow increase the static force of friction continuously. If no external force is applied and the surface is horizontal (no gravity effects come in), the direction of static friction can be to the left or to the right for the object-surface system in equilibrium.

If an external force of 1N is applied to the right, the static force of friction will be ACTING TO THE LEFT.(It cannot be to the right due to the nature of friction)

So it is impossible to have the applied force of 1 N to be in the same direction of the f force.

 

Unless I misunderstood your question, this should be the case.

[cyeokpeng]

Please define your forces consistently. I'm confused with which one is your externally applied force AND which one is the force of friction. Do your f refer to the friction force acting on the object or the externally applied force???

[Primarygun]

Never mind, I got the answer. It is b2.