Why can a rocket coast to the moon without its engine running?

[1234]

Why can a rocket travel to the moon with it's engine off?

i know that it's because space has no friction, air resistance so the rocket can travel when it's gained speed from traveling out of the atmosphere.
but are there any other reasons to that?

 

[somy]

Well, I think we can tell it as "the art of the nature".
Nature acts in a way that if no external force act on the body, its momentum is conserved.
It is the fact of the nature that we have detected it.
And we don't know why!
(Or maybe WE know and 'I' don't know!)

 

[Tide]

Why can a rocket travel to the moon with it's engine off?

i know that it's because space has no friction, air resistance so the rocket can travel when it's gained speed from traveling out of the atmosphere.
but are there any other reasons to that?

If you could leave your engines on you might get there and back a lot quicker! However, the fuel requirements would be enormous as chemical rockets are depressingly inefficient and you would need a LOT of fuel just to transport the fuel itself.

 

[geometer]

Why can a rocket travel to the moon with it's engine off?

i know that it's because space has no friction, air resistance so the rocket can travel when it's gained speed from traveling out of the atmosphere.
but are there any other reasons to that?

It's Newton's First Law in action - a body maintains its state of motion unless acted on by an outside force. Since, as you pointed out there is essentially no friction or air resistance in space, there is no force to change the rocket's state of motion.

 

[1234]

ohhh
the only reason is because no external force ?

 

[Alkatran]

No force means no acceleration. No acceleration means no change in speed. No change in speed means you can coast to the moon (well, very little change in speed in that case). QED