Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Have 1 quesiton

  1. Oct 6, 2004 #1
    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 travelling out of the atmosphere.
    but are there any other reasons to that?
  2. jcsd
  3. Oct 6, 2004 #2
    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!)
  4. Oct 6, 2004 #3


    User Avatar
    Science Advisor
    Homework Helper

    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.
  5. Oct 6, 2004 #4
    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.
  6. Oct 7, 2004 #5
    the only reason is because no external force ?
  7. Oct 7, 2004 #6


    User Avatar
    Science Advisor
    Homework Helper

    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
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?