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

Homework Help: Gravity & Weightlessness

  1. Apr 15, 2008 #1
    1. The problem statement, all variables and given/known data
    How far away from earth does a spacecraft have to be for the astonauts in it to be weightless?

    2. Relevant equations

    3. The attempt at a solution

    Is this correct:

    Since the gravitational force is a long range force, no matter what finite distance the spacecraft and earth are from each other, there will still be gravitational attraction. In order for the astronauts to be truly weightless the distance between the ship and the earth would have to be infinite.

    -I had second thoughts about what weightless meant. My book define weight as a normal force, so if the astronauts are floating around in the spacecraft, they have no normal force acting on them, but are they truly weightless?
  2. jcsd
  3. Apr 15, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    You are correct. There is still a gravitational force whatever the distance. But if the vehicle you are travelling in is accelerating at the same rate you are due to that force, then that force produces no normal force. You have to choose one definition or the other. They don't agree. Most people would call astronauts 'weightless', even though in low earth orbit the g force on them is not that much less than the ground.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook