Linked Questions

43
votes
6answers
16k views

Newton's 3rd law… hitting drywall (which I break) vs hitting a brick (which breaks me)?

According to the Third Newton's law of motion: For every action there is an equal and opposite reaction. So, I understand that if I hit a brick wall with $50\, \mathrm{lbs}$ of force, the brick ...
17
votes
4answers
4k views

Do the Earth and I apply the same gravitational force on each other in GR?

Our high-school teacher told us that the Earth pulls us with some force $F$ and we pull the Earth with the same force $F$. Within Newtonian physics this is true because of Newton's 3rd law, but let’s ...
16
votes
2answers
2k views

Why do people say that Hamilton's principle is all of classical mechanics? How to get Newton's third law?

From the principle of least (or stationary) action, we get that a classical system will evolve according to Euler-Lagrange equations: $$\frac{d}{dt}\bigg (\frac{\partial L}{\partial \dot{q_i}}\bigg) =...
14
votes
4answers
6k views

Does conservation of momentum really imply Newton's third law?

I often heard that conservation of momentum is nothing else than Newton's third law. Ok, If you have only two interacting particles in the universe, this seems to be quite obvious. However if you ...
0
votes
1answer
9k views

Violation of Newton's 3rd law and momentum conservation [closed]

Why and when does Newton's 3rd law violate in relativistic mechanics? Check this link.
6
votes
4answers
819 views

Newton third law and collinearity of forces

I have a doubt on the formulation of Newton third law. When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction ...
8
votes
3answers
1k views

Where does the reaction to action come from?

Third Newton's law, $F_{1->2} = -F_{2->1}$ So, how does a body react with the same force that it's receiving from the acting body? Is it the electric interactions at the subatomic level? When ...
14
votes
2answers
884 views

Is force a “real thing”, or a tool for explaining changes in measurable phenomena?

My physics text says that force is "an interaction between two bodies or a body and its environment." When an object undergoes acceleration we explain it with a force. But we don't measure force, ...
7
votes
3answers
353 views

Why there is no 3-body (or more generally $N$-body) fundamental force?

Fundamental forces are believed to be two body interactions. However, I found myself if there is no opportunity for a 3-body or more generally $N$-body "fundamental" force. Is there a proof that any ...
0
votes
2answers
537 views

WHY are Newton's Laws true?

Before you close this has a duplicate ! I've read some the related posts on this - but I have slightly different question. A lot of posts on stack exchange have demonstrated that Newton's laws can ...
-1
votes
1answer
674 views

Logical requirement of newton's third law [duplicate]

I'm describing a hypothetical universe. I'm assuming that the first law of newton holds true, that means there exists a inertial reference frame. Now the universe has three bodies. Second law is ...
3
votes
2answers
512 views

Internal potential energy and relative distance of the particle

Today, I read a line in Goldstein Classical mechanics and got confused about one line. To satisfy the strong law of action and reaction, $V_{ij}$ can be a function only of the distance between the ...
2
votes
2answers
78 views

Do internal forces always act along the line joining the particles?

For the rate of change of angular momentum of a system to be equal to the torque due to external forces, the torque due to internal forces should be zero. This will mathematically be possible only ...
0
votes
2answers
567 views

Conservation of linear momentum (classical mechanics and special relativity)

How did Newton deduce the law of conservation of linear momentum? Can it be derived only by Newton's laws, or does it follow from practical experiments? If the law of conservation of linear momentum ...
2
votes
0answers
348 views

N-body forces in classical mechanics

For a system of two interacting particles 1, 2 we get from the conservation of momentum $$ \dot{\bf{p_1}} + \dot{\bf{p_2}} = 0$$ ...

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