Understanding the Third Law of Newton — How can the forces be equal?

[chucho11028]

Homework Statement

understanding

Relevant Equations

n/a

Hello guys,
The third law says:
"For every action, there is an equal and opposite reaction. The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. "
so my question is about this statement:
The size of the forces on the first object equals the size of the force on the second object.
I know that:
F= a*m

But If I have 2 object with different masses, how is possible these two force are equal?
who determines the force? the masses or aceleration? however, a and m are part of the equation. How is possible the mass is not affecting?
For instance, the moon and the earth, two different masses but according to the 3th law, the forces must be the same, how is possible?

I will appreciate you guide me here

 

[PeroK]

Homework Statement:: understanding
Relevant Equations:: n/a

Hello guys,
The third law says:
"For every action, there is an equal and opposite reaction. The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. "
so my question is about this statement:
The size of the forces on the first object equals the size of the force on the second object.
I know that:
F= a*m

But If I have 2 object with different masses, how is possible these two force are equal?
who determines the force? the masses or aceleration? however, a and m are part of the equation. How is possible the mass is not affecting?
For instance, the moon and the earth, two different masses but according to the 3th law, the forces must be the same, how is possible?

I will appreciate you guide me here

It's a law of nature. The real question is: "why is it not possible"?

If you stopped the Earth and Moon, they would fall towards each other. The force on each would be the same. How is that not possible?

 

[chucho11028]

It's a law of nature. The real question is: "why is it not possible"?

If you stopped the Earth and Moon, they would fall towards each other. The force on each would be the same. How is that not possible?

I appreciate you took your time for answering but to be honest, it is not enought. I would like to know why the mass is not affceting this force
Regards,

 

[Doc Al]

For instance, the moon and the earth, two different masses but according to the 3th law, the forces must be the same, how is possible?

While, per Newton's 3rd and our understanding of gravity, the force is the same on each, that doesn't mean that the acceleration is the same. The same force can have a different "effect" on different bodies.

 

[etotheipi]

I appreciate you took your time for answering but to be honest, it is not enought. I would like to know why the mass is not affceting this force
Regards,

The product of the two masses does affect the magnitude of the force, specifically $F \propto m_1 m_2$. But both forces in the pair have the same magnitude.

Conservation of momentum can be derived from the fact that the magnitudes of these two forces are equal, and their directions opposite.

 

[PeroK]

I appreciate you took your time for answering but to be honest, it is not enought. I would like to know why the mass is not affceting this force
Regards,

Let's imagine that the Moon was one particle and the Earth was 100 particles. All the same mass. The force between the Moon and any of the 100 Earth particles is the same both ways. Let this force be $F$.

1) The total force on the Moon is $100 \times F$.

2) The total force on the Earth is $100 \times F$.

 

[wrobel]

the equation F=ma is not a definition of F

 

[chucho11028]

the equation F=ma is not a definition of F

I see, I think I start to udnerstand it. Thanks for your observation