Movement of planet in central force - hamilton mechanics

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SUMMARY

The discussion centers on deriving motion equations for a mass orbiting a larger mass using Hamilton mechanics, specifically in a polar coordinate system. The participant initially struggles with incorporating the Coriolis effect into their Lagrangian, which includes gravitational and centrifugal potentials. Ultimately, they conclude that the Coriolis force, being a pseudo force, does not need to be included in the Lagrangian for this inertial system, simplifying their calculations. The conversation also highlights the importance of using appropriate coordinate systems, suggesting that plane polar coordinates may not be suitable for a three-dimensional problem.

PREREQUISITES
  • Understanding of Hamiltonian mechanics and Lagrangian dynamics
  • Familiarity with polar coordinate systems in classical mechanics
  • Knowledge of gravitational potential and centrifugal force concepts
  • Basic grasp of pseudo forces, particularly the Coriolis effect
NEXT STEPS
  • Study Hamiltonian mechanics in-depth, focusing on applications in orbital dynamics
  • Learn about the derivation of equations of motion using Lagrangian mechanics
  • Explore the implications of using different coordinate systems in mechanics, such as spherical vs. plane polar coordinates
  • Investigate the role of pseudo forces in inertial vs. non-inertial reference frames
USEFUL FOR

Students and researchers in physics, particularly those focusing on classical mechanics, orbital dynamics, and Hamiltonian systems. This discussion is beneficial for anyone looking to deepen their understanding of motion in central force fields.

player1_1_1
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Hello, sorry for my English:D

Homework Statement


I am trying to find motion equations for a mass moving around a big mass (ex. planet around sun), assumption is that the mass in middle is static (so this can be reduced to moving of mass around central force in middle of cartesian system), and everything would be good but I don't know what to do with Coriolis effect (I am using polar system with angle and radius as generalised coordinates), using Hamilton mechanics

Homework Equations


Hamilton equations, differential equations, motion equations

The Attempt at a Solution


I have generalized coordinates in polar system: [tex]r,\phi,p_r,p_\phi[/tex] and I going to find lagrangial and hamiltonian, depending on general definition of both functions
[tex]\mathcal{L}\left(r,\phi,\dot r,\dot\phi\right)=\frac{m}{2}\left(\dot r^2+r^2\dot\phi^2\right)-U(r)[/tex]
now I find potential of centrifugal and central force
[tex]\mathcal{L}\left(r,\phi,\dot r,\dot\phi\right)=\frac{m}{2}\left(\dot r^2+r^2\dot\phi^2\right)+\frac{GMm}{r}-\frac{\ell^2}{2mr^2}-U\left(F_c\right)[/tex]
and now my problem is, what to do with general potential of Coriolis force? I know I can write is similar to electromagnetic force potential, but I don't know if Coriolis effect exist in this kind of motion (this system is inertial and Coriolis effect is connected with not inertial systems), when I know this, it will not be a big problem to find hamilton equations and finish divagations, so I only need answer for this, with explanation please;] thank you!
 
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player1_1_1 said:
I have generalized coordinates in polar system: [tex]r,\phi,p_r,p_\phi[/tex] and I going to find lagrangial and hamiltonian, depending on general definition of both functions
[tex]\mathcal{L}\left(r,\phi,\dot r,\dot\phi\right)=\frac{m}{2}\left(\dot r^2+r^2\dot\phi^2\right)-U(r)[/tex]
now I find potential of centrifugal and central force
[tex]\mathcal{L}\left(r,\phi,\dot r,\dot\phi\right)=\frac{m}{2}\left(\dot r^2+r^2\dot\phi^2\right)+\frac{GMm}{r}-\frac{\ell^2}{2mr^2}-U\left(F_c\right)[/tex]
and now my problem is, what to do with general potential of Coriolis force?

Why are you even bothering to add in these pseudo-potentials to your Lagrangian? Just work with the gravitational potential alone and derive the general equations of motion...if you want to then assume a circular or elliptical orbit and see what happens to your equations, it is a straight forward matter of adding this constraint into your Lagrangian by writing it in terms of a single independent variable ([itex]\rho[/itex] and [itex]\phi[/itex] will have a specific relationship to each other for any given orbit you choose to look at)

Also, why are you using plane polar coordinates (as opposed to spherical polar coordinates)...isn't this really a 3D problem? (The gravitational potential you are using is the 3D- potential)
 
Thanks for answer;]
one of assumption was that the planet is not moving in third dimension - only in one plane; for simplify divagations. Of course, I know that I can work only with gravity force potential, but I added centrifugal force potential to lagrangian because I also need to express this function only by [tex]r,\dot r[/tex] coordinates. I didnt write all the calculations because I only needed to know what to do with Coriolis effect. Summing up, it means that since coriolis force is pseudo force, I don't need it in my lagrangian (only gravity force potential)? thanks for help!
edit: well, I already found out an answer for this;] I must say - I asked stupid question :D
 
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