# Need Help Immediately Physics Lab Write-up

1. Dec 4, 2003

### Astronomer107

What is it meant by:

mr(1)V(1)= mr(2)v(2)
The quantity mrv is called the angular momentum of the planet. Is angular momentum of the planet conserved?

What do they mean conserved?? Thanks and sorry such short notice... my physics teacher soooo nicely gave us 2 days notice to finish all the labs for the 2nd marking period by tomorrow, which is in a half hour and I need some sleep, thanks.

2. Dec 4, 2003

### Ambitwistor

"Conserved" means "doesn't change with time".

3. Dec 5, 2003

### HallsofIvy

"mrv" is mass (m) times distance from the sun (r) times velocity (v).

Ordinary momentum itself is conserved (doesn't change as ambitwistor said) as long as there is no external force on the object.

That's not true for planets- the force of gravity from the sun is an external force.

Angular momentum is conserved if the force is perpendicular to the line of motion. Since planets move in ellipses rather than circles, that is not exactly true but the ellipses are so close to being circles that for most planets the difference is not very large.