Action reaction problem or Newton's 3 law

In summary, there is a bloc B on a surface S and a bloc A on top of bloc B. When we pull a rope towards the right, there is friction between all surfaces and the blocs remain stationary. The forces applied on bloc B are a normal force exerted by the surface S, a normal force exerted by bloc A, a gravitational force exerted by Earth, and a friction force exerted by bloc A to the right. Additionally, there is a friction force exerted by the surface S to the left, acting as a stabilizer to prevent bloc B from moving. These forces follow Newton's Third Law, where for every action there is an equal and opposite reaction.
  • #1
astrololo
200
3

Homework Statement



There is a bloc B that is on a surface S. A bloc A is on on the bloc B. We pull the rope towards the right. There is friction between all surfaces and the blocs stay stationary (They don't move). Identify all the forces which are applied on the bloc B.
http://imgur.com/Hzgc8pP

Homework Equations



No equations.

The Attempt at a Solution



I know that there is going to be a Normal upward, another normal that is downward because it is a reaction according to Newton's third law, the gravitational force downward. I think that there is going to be a friction force on the right because it is a reaction to the friction of bloc A. Now, I don't know what else to find... There is one missing...

Here is another image http://imgur.com/FYWfLgE[/B]
 
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  • #2
Consider any pair of Newton's Third Law action/reaction forces. The two forces never act on the same object.

So, for example, Block A pushes down on Block B, and Block B pushes up on Block A.
 
  • #3
Mister T said:
Consider any pair of Newton's Third Law action/reaction forces. The two forces never act on the same object.

So, for example, Block A pushes down on Block B, and Block B pushes up on Block A.
Yes but I don't see what else I can get... I'm only interested in object B and I got one pair of normal forces on the bloc A and B.
 
  • #4
Draw a diagram showing only Block B. On the diagram indicate only the forces that are acting on Block B.
 
  • #5
Mister T said:
Draw a diagram showing only Block B. On the diagram indicate only the forces that are acting on Block B.
I know that there is going to be a Normal upward, another normal that is downward because it is a reaction according to Newton's third law, the gravitational force downward. I think that there is going to be a friction force on the right because it is a reaction to the friction of bloc A.http://imgur.com/T9RXe3F
 
  • #6
astrololo said:
I know that there is going to be a Normal upward,

Exerted by the table.

another normal that is downward

Exerted by Block A

because it is a reaction according to Newton's third law,

(Every force is a reaction according to Newton's Third Law!)

the gravitational force downward.

Exerted by Earth.

I think that there is going to be a friction force on the right because it is a reaction to the friction of bloc A.

Exerted by Block A.

And one more ...

Hint: The net force on Block B must be zero because Block B is not in motion.
 
  • #7
Mister T said:
Exerted by the table.
Exerted by Block A
(Every force is a reaction according to Newton's Third Law!)
Exerted by Earth.
Exerted by Block A.

And one more ...

Hint: The net force on Block B must be zero because Block B is not in motion.
Oh, there's a friction force to the left because if there wasn't one, then the block B would be moving, right ? So it's not a reaction but more of a "stabilizer", right ?

Also, when I said "I think that there is going to be a friction force on the right because it is a reaction to the friction of bloc A." and you said : "Exerted by Block A." You mean that the block A is responsible for this reaction to the right, right ?
 
  • #8
astrololo said:
Oh, there's a friction force to the left because if there wasn't one, then the block B would be moving, right ? So it's not a reaction but more of a "stabilizer", right ?

Table pushes to the left on Block B, Block B pushes to the right on Table. It's an action/reaction pair. We call it friction.

Also, when I said "I think that there is going to be a friction force on the right because it is a reaction to the friction of bloc A." and you said : "Exerted by Block A." You mean that the block A is responsible for this reaction to the right, right ?

Correct!

Block A pushes to the right on Block B, Block B pushes to the left on Block A. It's an action/reaction pair. We call it friction.
 
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Likes astrololo
  • #9
Mister T said:
Table pushes to the left on Block B, Block B pushes to the right on Table. It's an action/reaction pair. We call it friction.
Correct!

Block A pushes to the right on Block B, Block B pushes to the left on Block A. It's an action/reaction pair. We call it friction.
Just one thing, the "S" isn't a table but a floor.

Forget it I understood what you meant Thanyou!
 

1. What is Newton's Third Law?

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object will also exert an equal force in the opposite direction on the first object.

2. Can you give an example of Newton's Third Law?

Yes, a classic example of Newton's Third Law is when a person is standing on a skateboard and pushes against a wall. The person exerts a force on the wall, and the wall exerts an equal force back on the person, causing them to move in the opposite direction.

3. How does Newton's Third Law relate to everyday life?

Newton's Third Law can be seen in many everyday situations, such as when we walk or run. When we push against the ground with our feet, the ground pushes back with an equal and opposite force, allowing us to move forward. It also applies to throwing or catching a ball, as the force we exert on the ball is equal and opposite to the force the ball exerts on our hand.

4. Are there any exceptions to Newton's Third Law?

No, Newton's Third Law is a fundamental law of physics and applies to all interactions between objects. However, in certain situations, the forces may not cancel out completely, resulting in a net force and causing the objects to accelerate.

5. How is Newton's Third Law important in understanding motion and forces?

Newton's Third Law helps explain how forces cause objects to move and accelerate. It also helps us understand how objects interact with each other and how forces can be balanced or unbalanced. This law is essential in understanding the behavior of objects in motion and is a fundamental concept in physics.

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