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Gravity and Jupiter's moon Io

  1. Apr 15, 2013 #1
    1. The problem statement, all variables and given/known data

    Io (pronounced “EYE oh”) is one of Jupiter’s moons discovered by Galileo. Io is slightly larger
    than Earth’s Moon.

    The mass of Io is 8.92*1022 kilograms
    and the mass of Jupiter is 1.9*1027
    kilograms. The distance between the
    centers of Io and Jupiter is r = 4.22*10 meters.

    1. Calculate the magnitude of the gravitational force of
    attraction that Jupiter exerts on Io.

    2. Calculate the magnitude of the acceleration of Io due
    to the gravitational force exerted by Jupiter.

    2. Relevant equations

    Fg = G m1 m2/r2

    Io = m1 = 8.92*1022
    Jupiter = m2 = 1.9*1027
    r = 4.22*10
    G = 6.67*10-11

    3. The attempt at a solution

    1. Fg = (6.67*10-11)(8.92*1022)(1.9*1027) / (4.22*108)2

    = 6.36*1022N

    2. How can i find the acceleration of Io?
    Do i use F=ma => a=F/m => a = (6.35*1022) / (8.93*1022) = 7.12*1043 ?? this does not seem right.
  2. jcsd
  3. Apr 15, 2013 #2
    Looks like you multiplied instead of dividing in the last line of your post.
  4. Apr 15, 2013 #3
    Thanks Jesse, i kept on making that mistake. Until i realized it was the way i typed it into my calculator...

    2. How can i find the acceleration of Io?
    Do i use F=ma => a=F/m => a = (6.35*1022) / (8.93*1022) = 0.71m/s2?

    However, i still would like to know if i have used to correct method and achieved the correct result?
    Considering earths moon's gravitational attraction (roughly 1.6m/s2), compared to Io the larger moon, you would expect Io to have a slightly greater gravitational attraction due to its greater mass. Therefore i am assuming that my answer is still not correct.
    Last edited: Apr 15, 2013
  5. Apr 16, 2013 #4


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    As you can see from the equations you have used, the acceleration of the satellite towards the parent body is independent of the mass of the satellite. It depends on the mass of the parent and distance from it. Although Jupiter is so much more massive than the Earth, Io's extra distance from it more than makes up for this.
  6. Apr 16, 2013 #5
    I see, i was not taking the distance into consideration in my assumption. Io is farther away from Jupiter than is the Moon from Earth.Therefore Io's force of gravity will be less then i expected.
    In addition I have only calculated the acceleration of the force of gravity towards Io's surface and not that of Io's acceleration towards the parent body Jupiter.

    Therefore i haven't answered the question correctly. I can not seem to figure out the answer to this question, i feel like i am missing some key point of information... i understand i must calculate the Fg of Jupiter and then divide it by the distance "r" (assuming i also figured out how to implement the strength decrease of Fg per distance).
  7. Apr 16, 2013 #6


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    No, you did it correctly (apart from the numerical error). You computed the force of attraction between Jupiter and Io, then you divided by the mass of Io get the acceleration Io experiences as a result of that force.
  8. Apr 16, 2013 #7
    Thats right, i calculated the Fg between m1 and m2 and divided it by Io's mass to produce the acceleration of that force.
    Not solely Io's Fg, because in order to do that i would have needed to calculate "Fg = GmIo / r2" (where r would be the radius of Io's center to its surface).

    Thank you for clearing that up :)
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