Kepler problem: flows generated by constants of motion

In summary, the flows generated by the functions m_i and W_i are canonical transformations and they are also point transformations.
  • #1
Clausius
4
0
Consider the Hamiltonian of Kepler problem
[tex] H(\boldsymbol{r},\boldsymbol{p})=
\frac{|\boldsymbol{p}^2|}{2\mu}
+\frac{\alpha}{|\boldsymbol{r}|},
\qquad \mu>0>\alpha,[/tex]
where [tex]\boldsymbol{r}\in M=\mathbb{R}^3\setminus\{ 0 \}, \ (\boldsymbol{r},\boldsymbol{p})\in T^*M[/tex] and
[tex]|\boldsymbol{r}|=\sqrt{r_1^2+r_2^2+r_3^2}.[/tex]
The quantities
[tex] \boldsymbol{m}=\boldsymbol{r}\times\boldsymbol{p},
\qquad \boldsymbol{W}=\boldsymbol{p}\times\boldsymbol{m}+\mu\alpha\frac{\boldsymbol{r}}{|\boldsymbol{r}|}[/tex]
are constants of motion, as is well known.

My question is: how can I prove that the flows generated by the functions m_i and W_i, i=1,2,3 are canonical transformations?
Moreover, are such transformations point transformations?

A canonical transformation [tex]\Phi: T^*M\to T^*M[/tex] is a point transformation if it is induced by a transformation [tex]\phi:M\to M,[/tex]
so that
[tex]\Phi(\boldsymbol{r},\boldsymbol{p})=
(\phi(\boldsymbol{r}),\phi^{*-1}),
\ \phi^*_i=
\frac{\partial\phi_i}{\partial r_j}p_j.[/tex]
 
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  • #2
In order to prove that the flows generated by the functions m_i and W_i are canonical transformations, we must first determine the generating functions of these flows. Generating functions of the form S(\boldsymbol{r},\boldsymbol{q}) can be used to define canonical transformations through the equations \boldsymbol{p}=\frac{\partial S}{\partial\boldsymbol{q}},\ \ \boldsymbol{r}=\frac{\partial S}{\partial\boldsymbol{p}}.We then use Hamilton's equations\frac{d\boldsymbol{r}}{dt}=\frac{\partial H}{\partial\boldsymbol{p}}and\frac{d\boldsymbol{p}}{dt}=-\frac{\partial H}{\partial\boldsymbol{r}}to prove that the flows generated by the functions m_i and W_i do indeed generate canonical transformations.To show that the transformations are point transformations, we must additionally prove that there exists a transformation \phi:M\to M such that\Phi(\boldsymbol{r},\boldsymbol{p})=(\phi(\boldsymbol{r}),\phi^{*-1}),\ \phi^*_i=\frac{\partial\phi_i}{\partial r_j}p_j.This can be established by solving the Hamilton-Jacobi equation for the generating functions S(\boldsymbol{r},\boldsymbol{q}) and then constructing the corresponding transformation \phi:M\to M from the solution.
 

Related to Kepler problem: flows generated by constants of motion

1. What is the Kepler problem?

The Kepler problem is a mathematical model used to describe the motion of two objects that are gravitationally attracted to each other, such as a planet orbiting around a star. It is named after the astronomer Johannes Kepler, who first described the laws governing planetary motion.

2. What are flows generated by constants of motion?

Flows generated by constants of motion refer to the trajectories or paths followed by objects under the influence of a constant force, such as gravity. These paths are determined by the conservation of certain physical quantities, such as energy and angular momentum, which remain constant throughout the motion.

3. How are the constants of motion related to the Kepler problem?

In the Kepler problem, there are three constants of motion: energy, angular momentum, and the Laplace-Runge-Lenz vector. These quantities determine the shape, size, and orientation of the elliptical orbit followed by an object around a central mass. They also allow us to predict the future positions and velocities of the object based on its current state.

4. What are the implications of the Kepler problem for planetary orbits?

The Kepler problem and its associated laws have significant implications for our understanding of planetary orbits. By studying the motion of planets, we can determine their masses, distances from the sun, and other important characteristics. This information is crucial for predicting future events, such as planetary conjunctions and eclipses, and for space exploration missions.

5. Are there any real-world applications of the Kepler problem?

Yes, the Kepler problem has many real-world applications beyond the study of planetary motion. It is used in fields such as celestial mechanics, astrodynamics, and satellite orbit prediction. It also has applications in spacecraft trajectory planning and in the development of efficient and accurate numerical methods for solving complex physical systems.

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