- #1
krishna mohan
- 117
- 0
Hi...
I was reading through the second edition of the book Galactic Dynamics from Binney and Tremaine.
Chapter 3 :eqns 3.8 and 3.9.
3.8 says
[tex]r^2 \frac{d \phi}{dt}=L=constant[/tex].
Then 3.9 writes
[tex]\frac{d}{dt}=\frac{L}{r^2}\frac{d}{d\phi}[/tex]
But is this correct? For example, if I act this on r, the radial coordinate, I get
[tex]\frac{dr}{dt}=0[/tex]
For a general orbit in a central force, r is not a constant.
So is there a mistake in the book, or am I missing something?
I was reading through the second edition of the book Galactic Dynamics from Binney and Tremaine.
Chapter 3 :eqns 3.8 and 3.9.
3.8 says
[tex]r^2 \frac{d \phi}{dt}=L=constant[/tex].
Then 3.9 writes
[tex]\frac{d}{dt}=\frac{L}{r^2}\frac{d}{d\phi}[/tex]
But is this correct? For example, if I act this on r, the radial coordinate, I get
[tex]\frac{dr}{dt}=0[/tex]
For a general orbit in a central force, r is not a constant.
So is there a mistake in the book, or am I missing something?