
#19
Nov1012, 03:08 PM

P: 10





#20
Nov1012, 05:05 PM

P: 5,462

I clearly have a different definition of the principle of conservation of linear momentum than whatever you are thinking of. 



#21
Nov1012, 08:18 PM

Sci Advisor
P: 2,470

harrylin, you solve a lot of manybody problems analytically? Every single real world application of principles of physics is numerical. So yes, ability to take your problem and put in the form you can feed to a solver of some kind is what determines whether the method is useful or not.
Studiot, do you have a point? You are jumping all over the place and making counter points that have no common thesis. OP asked about forces. Fact is, nearly all of the physics has moved away from the force as a primary concept. Even in Classical Mechanics, once you move past Newtonian Physics, individual forces is not something you frequently consider. Newton's Laws have their applications. They do make many problems simpler. But they are neither the dominant explanation nor a dominant method even in mechanics. Hamilton's Principle and Conservation Laws are used instead. I have provided arguments and explanation for this position. You just pick at individual phrases rather than have any sort of kind of point. That's not how you construct a counterargument. 



#22
Nov1012, 10:12 PM

Engineering
Sci Advisor
HW Helper
Thanks
P: 6,347

Limiting yoursefl to only one philosophical toolkit doesn't have any advantage than I can see. The more ways you can use to intuitively "see" what's going on the better, IMO. 



#23
Nov1112, 04:18 AM

P: 3,178





#24
Nov1112, 04:35 AM

P: 3,178

However, as others already mentioned, no momentum is lost or gained by an object in static cases that force is applied. Force is in classical mechanics a more general concept than change of momentum. Do the links help or do you need more? PS You forgot to elaborate how the Coulomb interaction affects contact force and Hooke's law. 



#25
Nov1112, 05:26 AM

Sci Advisor
P: 2,470

Lagrangian mechanics generalizes trivially. Newtonian mechanics does not. 



#26
Nov1112, 06:36 AM

P: 977

Any possible continuous symmetry can be described by the invariance of lagrangian under certain transformation.It is really helpful when one does not get ideas from newtonian eqn.lagrangian can be written down without having much detail of forces which is certainly not the case with newtonian mechanics.




#27
Nov1112, 11:42 AM

P: 5,462

Since those who believe momentum to be one of the fundamental quantites have avoided my previous question about fluid dynamics I suppose that they will avoid this simple one as well.
Consider an isolated universe, empty except for a single particle. What is the momentum of that particle? 



#28
Nov1112, 01:13 PM

Sci Advisor
P: 2,470

You did not actually ask a question about fluid mechanics. Nor do you have a thesis still. What exactly are you arguing? What are your points and what are your arguments for these points?
Because I don't know your thesis, I am forced to guess your point about a lone particle. I'm guessing, you are trying to say "Force is absolute. Momentum is not." Well, you are wrong. If you take Relativity into account, force is framedependent just like momentum is. If you don't, then in Classical Mechanics I'm free to chose an absolute coordinate system and measure absolute momentum. Yes, even for one particle in the universe. So either both are relative or both are absolute depending on the kind of physics we are talking about. 



#29
Nov1112, 01:16 PM

Mentor
P: 16,477





#30
Nov1112, 02:19 PM

P: 5,462





#31
Nov1112, 04:41 PM

Sci Advisor
P: 2,470

Fluid dynamics is derived from classical field theory. I still have no idea what it is that you are asking. The entire topic is an example of how you work with momenta directly without ever considering forces.




#32
Nov1112, 06:22 PM

P: 5,462

On my last question. In my opinion momentum in my uniparticular universe is indeterminate since the particle's velocity is indeterminate. 



#33
Nov1112, 06:40 PM

Mentor
P: 16,477





#34
Nov1112, 06:42 PM

P: 5,462

A definite velocity relative to what?




#35
Nov1112, 06:44 PM

Mentor
P: 16,477

Relative to the reference frame. That is how velocities are always defined.




#36
Nov1112, 06:46 PM

P: 5,462

So where in this empty infinite universe is the origin of this reference frame?



Register to reply 
Related Discussions  
How many conservation laws ?  General Physics  8  
Conservation Laws  Classical Physics  13  
Conservation Laws  Special & General Relativity  13  
Conservation Laws  Advanced Physics Homework  2  
I need help with Conservation Laws!  Introductory Physics Homework  1 