Solving Constants of Motion for Particle in 3D - No Quotes

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The discussion focuses on deriving the Hamiltonian function for a particle moving in three dimensions under a conservative force with potential energy V(r). The Hamiltonian is expressed as H = P²_r/(2m) + P²_θ/(2mr²) + P²_φ/(2mr²sin²θ) + V(r). It is established that P_φ is a constant of motion due to its cyclic nature. Participants discuss methods for identifying other constants of motion, suggesting the use of Poisson brackets to analyze the relationship between the Hamiltonian and the constants. The conversation emphasizes the importance of understanding these concepts for solving related physics problems.
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[SOLVED] Constants Of Motion

A Particle of mass m moves in three dimensions under the action of a conservative force with potential energy V(r).Using the sperical coordinates r, \theta,\phi, obtain the hamiltonian function for the system.
Show that P_{\phi} , \frac{P^{2}_{r}}{2m} + \frac{P^{2}_{\phi}}{2mr^{2}sin^{2}\theta} + V(r) and P^{2}_{\theta} + \frac{P^{2}_{\phi}}{sin^{2}\theta} are constants of motion.

I found the hamiltonian, H = \frac{P^{2}_{r}}{2m} + \frac{P^{2}_{\theta}}{2mr^{2}} + \frac{P^{2}_{\phi}}{2mr^{2}sin^{2}\theta} + V(r).


Since \phi is cyclic we have P_{\phi}^{'}=0 or P_{\phi} is a constant of motion. I don't have much idea about the rest. Do u people have any suggestions? Thanks in advance..
 
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Hi, abeen,

Welcome to PF.

From the way you phrased your questions, it sounds like you are seeking advice for how to attack a homework problem. If so, there's a special forum at PF for that (look up above for the "sticky"). If not, we can help you right here.
 
abeen said:
. I don't have much idea about the rest. Do u people have any suggestions? Thanks in advance..

Hint: Poisson bracket
 
siddharth said:
Hint: Poisson bracket

Thanks.Can you please give me a brief account of the methods for identifying a constant of motion.
 
abeen said:
Thanks.Can you please give me a brief account of the methods for identifying a constant of motion.

That was the hint. If F(p,q) is a constant of motion and H is the hamiltonian, what can you conclude about {H,F} ?
 
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