## Question on Normal Force

Hi everyone.

I just started learning some basic Newtonian mechanics and several questions arose.
Hope you could help me with it. Thank you.

1. What exactly constitutes the "normal force".

It says that normal force is perpendicular to the surface where the object is placed but I don't really understand what exactly is this force.

2. Is "at rest" categorized as motion as well? Since Newton's First Law states that force doesn't produce motion..whereas it changes motion. Then if at rest is not considered motion then the law doesn't hold right?

3. Can frictional force produce motion?
We did those free body diagrams. I was wondering what would happen if you keep increasing the frictional force while keeping other forces the same. Wouldn't there be a non-zero net force then?
 I'm very new to this myself but I think I can answer your question on what would happen if you increased the force of friction. Consider placing an object on a low friction surface. Will it move? No, not without a sufficient applied force. Then place the object on a super high friction surface. Will it move? No but it is now even less inclined to move as a result of the increased friction. No negative movement occurs :)

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 Quote by FakeGeek 1. What exactly constitutes the "normal force". It says that normal force is perpendicular to the surface where the object is placed but I don't really understand what exactly is this force.
Push your hand against a book, or any surface. Do you feel something pushing back? That's the normal force.

 Quote by FakeGeek 2. Is "at rest" categorized as motion as well? Since Newton's First Law states that force doesn't produce motion..whereas it changes motion. Then if at rest is not considered motion then the law doesn't hold right?
If an object is at rest, there are still forces acting on the object. Newton's 1st Law states that "Every body remains in a state of rest or uniform motion (constant velocity) unless it is acted upon by an external unbalanced force." Therefore, if the object is at rest, the forces acting on it are balanced.

 Quote by FakeGeek 3. Can frictional force produce motion? We did those free body diagrams. I was wondering what would happen if you keep increasing the frictional force while keeping other forces the same. Wouldn't there be a non-zero net force then?
Friction's task is to oppose motion or attempted motion. So you can't just "increase" the frictional force to an indefinite amount. It will provide just enough counteracting force necessary to prevent motion.

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## Question on Normal Force

Welcome to the Physics Forums!
 Quote by FakeGeek Hi everyone. I just started learning some basic Newtonian mechanics and several questions arose. Hope you could help me with it. Thank you. 1. What exactly constitutes the "normal force". It says that normal force is perpendicular to the surface where the object is placed but I don't really understand what exactly is this force.
In basic mechanics, there are 2 types of forces: one is the 'action at a distance force' like the gravity force acting on an object (the 'weight' force), and the other is a 'contact' force, which can occur when 2 objects are 'touching' each other, like a tension force, a pushing force, a friction force, spring force, or normal force (as you have described). The best example of the normal force is the force pusing up on a block resting on a horizontal table. The weight of the block acts down, and since the body is at rest, Newton 1 says there can be no unbalanced net force acting on that object. The normal force is the upward force of the table on the block, balancing the weight force acting down, such that F_net = 0. Without the normal force, the block would fall through the table.
 2. Is "at rest" categorized as motion as well? Since Newton's First Law states that force doesn't produce motion..whereas it changes motion. Then if at rest is not considered motion then the law doesn't hold right?
I think you're misunderstanding the laws. Newton 1 refers to a body at rest or moving along an axis at constant speed. There is no net force acting on such an object, whether at rest, or moving at constant speed in a 'straight' line along an axis. Newton 2 says that an unbalanced net force will give that object accelerated motion in the direction of the net force.
 3. Can frictional force produce motion? We did those free body diagrams. I was wondering what would happen if you keep increasing the frictional force while keeping other forces the same. Wouldn't there be a non-zero net force then?
Yes. A good example is a car given accelerated motion forward by tires applying a backward force on the road, which in turm places a friction force acting forward on the tires. Without this force, the car would hopelessly spin its wheels in place and go nowhere.
 Thanks a lot guys. But I still don't get what exactly is this normal force. I understand that it must exist and perpendicular to the surface otherwise the object will accelerate down when placed on a flat surface. But WHAT TYPE OF FORCE IS THE NORMAL FORCE..it can't just be there right? doesn't it have to be produced by something? like electromagnetic force or force of gravity?

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 Quote by FakeGeek Thanks a lot guys. But I still don't get what exactly is this normal force. I understand that it must exist and perpendicular to the surface otherwise the object will accelerate down when placed on a flat surface. But WHAT TYPE OF FORCE IS THE NORMAL FORCE..it can't just be there right? doesn't it have to be produced by something? like electromagnetic force or force of gravity?
Newton's third law: push on something, it pushes you back with a force equal in magnitude.

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 Quote by FakeGeek Thanks a lot guys. But I still don't get what exactly is this normal force. I understand that it must exist and perpendicular to the surface otherwise the object will accelerate down when placed on a flat surface. But WHAT TYPE OF FORCE IS THE NORMAL FORCE..it can't just be there right? doesn't it have to be produced by something? like electromagnetic force or force of gravity?
It is an electrostatic force, due to the protons and electrons from the two objects being close together.