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

G-force on ground

  1. Aug 1, 2014 #1
    I was looking at this graph and wondering what the value of the graph would be before the engines turn on. Should it be 1 g-force or 0 g-force? (the "force" in g-force being a misnomer as it is a measure of acceleration, not force) Below are arguments for each:

    Why it should be 1 g-force: We experience 1 g-force of acceleration on earth's surface. The astronauts would also experience 1 g-force before the engines turn on.

    Why it should be 0 g-force: The acceleration of the rocket (in m/s^2) is clearly 0 while the rocket is still on the ground. 0 m/s^2 corresponds to 0 g-force.

    Which is the correct interpretation? Or is this just a problem of choosing your zero? In that case what is the convention?
  2. jcsd
  3. Aug 1, 2014 #2


    User Avatar
    Science Advisor
    Gold Member

    That's "proper acceleration":

    That's "coordiante acceleration" in the rest frame of the surface:

    If it says "G-force" it probably means proper acceleration. Also because it drops to 0 during stage changes. Coordinate acceleration would drop to -1g.
  4. Aug 1, 2014 #3
    Ah I should have paid attention to the stage changes! No ambiguity there. Thank you!
  5. Aug 1, 2014 #4


    User Avatar
    Science Advisor
    Gold Member

    And also the figure caption:

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