Paper 2, Section I, B

Classical Dynamics
Part II, 2020

A particle of mass mm has position vector r(t)\mathbf{r}(t) in a frame of reference that rotates with angular velocity ω(t)\boldsymbol{\omega}(t). The particle moves under the gravitational influence of masses that are fixed in the rotating frame. Explain why the Lagrangian of the particle is of the form

L=12m(r˙+ω×r)2V(r).L=\frac{1}{2} m(\dot{\mathbf{r}}+\boldsymbol{\omega} \times \mathbf{r})^{2}-V(\mathbf{r}) .

Show that Lagrange's equations of motion are equivalent to

m(r¨+2ω×r˙+ω˙×r+ω×(ω×r))=Vm(\ddot{\mathbf{r}}+2 \boldsymbol{\omega} \times \dot{\mathbf{r}}+\dot{\boldsymbol{\omega}} \times \mathbf{r}+\boldsymbol{\omega} \times(\boldsymbol{\omega} \times \mathbf{r}))=-\boldsymbol{\nabla} V

Identify the canonical momentum p\mathbf{p} conjugate to r\mathbf{r}. Obtain the Hamiltonian H(r,p)H(\mathbf{r}, \mathbf{p}) and Hamilton's equations for this system.