Another conservation of momentum question, but this one involves gravity

[kashiark]

If you throw a baseball up on the moon, and it comes down, how is momentum conserved?

 

[Doc Al]

Momentum of the "baseball-Moon" system will be conserved, but the momentum of the baseball alone would not.

 

[kashiark]

How? I don't understand.

 

[Doc Al]

How? I don't understand.

How what? What specifically don't you understand?

What are the conditions under which momentum is conserved?

 

[kashiark]

Does the moon gain momentum in the direction the ball was going?

 

[Doc Al]

The moon and baseball exert equal and opposite forces on each other. If one gains momentum in one direction, the other must lose momentum in that same direction (or gain it in the opposite direction).