1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Newton's Law of Universal Gravitation

  1. Aug 9, 2010 #1
    1. The problem statement, all variables and given/known data
    I am doing a lab-"Kepler's Laws and Newton's Law of Universal Gravitation". There is an image representing various positions, at equal intervals, of a satelitte in an elliptical orbit around the earth. A list of planets and their radi and periods are given. I have calculated acceleration using two formulas a=GMm/r^2 and a=4pi^2r/T^2
    Question states: "Calculate acceleration using the two equations and compare the results. Do your results confirm Newton's law of universal gravitation?"

    2. Relevant equations

    3. The attempt at a solution
    Ex. of results: accleration obtained for Venus using 1st equation= 5.5407*10^24 and using 2nd equation=0.0113286
    I was expecting them to be the same...please help
  2. jcsd
  3. Aug 9, 2010 #2


    User Avatar
    Gold Member

    a=GMm/r^2 is wrong

    go back to the general equation

    m1=mass of Venus
    m2=mass of satellite



    compare to the one you originally had (a=GMm/r^2)
  4. Aug 13, 2010 #3
    But mass of the satellite isn't given..?
  5. Aug 13, 2010 #4
    Wait...so as you said to use a=Gm1/r^2...for venus I got a=(6.67*10^-11)(4.8690*10^24)/(1.08*10^11)^2= 2.784*10^-8
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook