Do Multiple Reaction Forces Create Infinite Chains in Newton's Third Law?

In summary, the conversation discusses Newton's third law and its application to various scenarios involving forces on different bodies. It also addresses potential misconceptions about the concept and clarifies the relationship between action and reaction forces. The conversation concludes by mentioning the need to use Newton's second law in addition to the third law for a complete analysis of forces.
  • #1
AmrD
1
0
I have a 2 questions regarding Newton’s third law and I will explain them using examples:

1. Body A is pushing against Body B with a force F(AB), Now body B will push against body A with a reaction force F(BA) equal but opposite to F(AB). Now shouldn’t be another reaction force F2(AB) due to the action of the reaction force F(BA) and another reaction force F2(BA) as a reaction to that reaction !

2. Three bodies A, B and C setting on a frictionless surface in the order A, B and C. A is pushing on B with F(AB)
First, is it true that B will also push on C with the same force F(AB) and if that is true shouldn’t C also exert a reaction force on B with the magnitude F(AB).

I think I am misunderstanding the concept and how are forces transmitted through the bodies and how does Newton’s third law apply here.

I need some help here.

Thanks in advance.
 
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  • #2
AmrD said:
I1. Body A is pushing against Body B with a force F(AB), Now body B will push against body A with a reaction force F(BA) equal but opposite to F(AB). Now shouldn’t be another reaction force F2(AB) due to the action of the reaction force F(BA) and another reaction force F2(BA) as a reaction to that reaction !
There are just two bodies and thus two forces involved: F(AB) and F(BA). Those forces are equal and opposite. (Using your notation, F2(BA) is the same force F(BA).)

2. Three bodies A, B and C setting on a frictionless surface in the order A, B and C. A is pushing on B with F(AB)
First, is it true that B will also push on C with the same force F(AB) and if that is true shouldn’t C also exert a reaction force on B with the magnitude F(AB).
No, it is not true. At least it's not necessarily true. If those blocks are held in place so they have no acceleration, then the force that A exerts on B must equal the force that C exerts on B. Nonetheless, they are not 'action-reaction' pairs.

I think I am misunderstanding the concept and how are forces transmitted through the bodies and how does Newton’s third law apply here.
Using your three bodies (let's assume blocks on a frictionless surface) as an example. The Newton 3rd law pairs are:
(1) A pushes on B and B pushes on A
(2) B pushes on C and C pushes on B

The force between A and B does not necessarily equal the force between B and C. To fully analyze the forces exerted, you'll need Newton's 2nd law as well as the 3rd.
 

1. What is Newton's Third Law of Motion?

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

2. How do action and reaction forces affect motion?

Action and reaction forces do not cancel each other out, but rather they act on different objects. This results in a change in the motion of both objects. The direction of the forces will be opposite, but the magnitudes will be equal.

3. Can action and reaction forces act on the same object?

No, action and reaction forces always act on different objects. This is because for every action, there must be an equal and opposite reaction on a different object.

4. Are action and reaction forces always the same type of force?

No, action and reaction forces can be of different types. For example, if a person pushes a wall, the action force is a muscular force while the reaction force is a contact force between the person's hand and the wall.

5. Do action and reaction forces always have the same magnitude?

Yes, according to Newton's Third Law, action and reaction forces always have the same magnitude. This means that if object A exerts a force of 10 N on object B, then object B will exert a force of 10 N back on object A in the opposite direction.

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