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

Question reguarding gravitational pull

  1. Mar 28, 2009 #1
    Hey there, firstly i'll just say to start i've not studied general relativity at all, and the answer to my question may lie there, but i'll ask anyway;

    Well I was thinking about the gravitational equation;

    F (1,2) = m1m2G/d²

    However putting the earth & a person in there gives an absolutely ridiculously high result, and yet we know for a fact that the pull of gravity on us is constant (10 ms ish), by just using really rough internet figures i get

    (70 (mass of avg person) * 5.9 * 10^24 (earth mass) * G)/ 6377000^2 (dist from core - surface of the earth)

    = 583 ish ms? A ridiculous answer

    Any reason for this? I don't think i've gone much wrong, not enough to cause that :eek:

    Thanks in advance for any help

    Edit :JEEZ MEGA FAIL ON MY PART - F = MA, LAWLLLLL, diving by 70 gives a very good answer for gravity -

    does this then mean that 9.8 isn't constant? And it is indeed dependant on mass, but it makes almost no difference whatsoever - sorry for failthread
     
  2. jcsd
  3. Mar 28, 2009 #2
    A person with a mass of 70 kg has a weight close to 700 newtons on earth. That's the gravitational force exerted by the earth on the person. Your method should give you a number close to that expected answer.
     
  4. Mar 28, 2009 #3
    G m_earth / (r_earth)^2

    = (6.67 X 10^-11 N m^2/kg^2) ( 5.98 X 10^24 kg) / (6.37 X 10^6 m)^2

    = 9.83 kg m/s^2
     
  5. Mar 28, 2009 #4
    So....it's not constant? :P Didnt really get the 2nd post
     
  6. Mar 29, 2009 #5

    DaveC426913

    User Avatar
    Gold Member

    Where are you incorporating G, which equals 6.67*10^-11?
     
  7. Mar 29, 2009 #6
    Yeah sorry i forgot to edit the original post - i did get it in the end, just forgot to divide by mass xP, got 9.75 ish which is awesome considering the mega-rounding i did with the wiki figures, it's just really nice to see these awesome equations work using them yourself! Thanks guyz
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question reguarding gravitational pull
Loading...