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Moon -> Earth (Gravitational Pull help any comment welcome

  1. Feb 11, 2009 #1
    Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!

    1. The problem statement, all variables and given/known data

    At what distance (AU) does a spacecraft leaving the gravity of the earth travelling toward the moon balance the gravity of the moon? I.E. What distance in (AU) will the object begin being affected by the Moon's gravity and not that of the Earth's strong gravity?

    Earth Mass 5.9 x 10 24/pwr kg
    Earth Gravitational Parameter, Gm earth: 3.986004418 x 10 12/pwr km/squared
    Earths Eccentricity: .081819301

    Moon Mass 7.3 x 10 22/pwr kg
    Moon Gravitational field Parameter: J2= +0.02027 x 10/-3pwr
    Distance between the earth and the moon: 7.84 x 10 8/pwr meters





    2. Relevant equations

    Earth gravitational pull = 0? (At what point?)
    Moon gravition pull = 0 (At what point?)

    Example: Apollo 13, system failure. Astronaut had to do one last safe burn to enter a safe earth orbit in order to avoid spinning out into infinity.



    3. The attempt at a solution
    I am struggling writing (pwr) in this blog if someone can tip me off on how to write them I can give my progress on this problem!!!! Thanks for those interested parties that provide feedback, positive, negative or troll!!!

    -James
    Space Coast, FL
     
  2. jcsd
  3. Feb 11, 2009 #2

    LowlyPion

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    Re: Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!

    Welcome to PF.

    As to your problem draw a picture and recognize that De and Dm sum to the distance between Earth and Moon.

    Your equations simplify then to

    Me/De2 = Mm/Dm2

    and

    De + Dm = Dem

    If you click the Quote button you can see the codes in all the posts.
     
  4. Feb 11, 2009 #3
    Re: Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!

    The question is at what radius r will the gravitational forces of the Earth and the Moon be equal. Do you know the formula for the gravitational force between two objects?

    [/QUOTE]

    The object will always be affected by both the Earth and the Moon's gravity. The question is which force is larger.
     
  5. Feb 11, 2009 #4
    Re: Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!


    Wow mate~!! Awesome response time and data points. I am curious if you could direct me to a web site, online source, etc. where that formula is from? I dont understand the variables of that formula. Both of the posters thus far are helping me see outside the box. I cant belv this web site its so awesome. I called my mom with a headache from class today and she went onto google.com and found this site. Then tonight I joined it... Wow... Gotta keep pencilin I guess But i dont understand the variables of the formula yet...

    -Happy James
     
  6. Feb 11, 2009 #5

    LowlyPion

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    Re: Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!

    http://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation

    Since the 2 forces must be equal at the tipping point,

    GMem/De2 = G*Mmm/Dm2

    That simplifies to the equation provided. (The m of the object simply cancels along with G)

    The D's are distances to the centers of the earth or moon.
     
  7. Feb 11, 2009 #6
    Re: Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!



    SPECIFICALLY WRITTEN: At what distance from the earth to the moon is the earth's gravitational force equal to the earth's gravitational force of the moon??? This would be the accurate question I think my Aerospace Systems II Prof. is reaching for..
     
  8. Feb 11, 2009 #7
    Re: Moon --> Earth (Gravitational Pull... help plz any comment welcome!!!

    I promise I am not mentally challenged. I am struggling with my book to find the attributes for the formula you gave me. I am not asking for the answer. I am asking if you can point me in the right direction by way of an outside web site. Where I can locate the data? I feel bad writing another help question really, but I see how this can be a valuable resource for assistance. I want to do the problem and find the answer but I cant seem to locate the data to plug into the formula.

    -Last cry for help.
    James
    Space Coast, FL
     
  9. Feb 11, 2009 #8

    LowlyPion

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