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Confused about forumla

  1. Nov 12, 2011 #1
    F = Gmm'/r^2

    Does this explain the sum or total gravitational force between two bodies?
     
  2. jcsd
  3. Nov 12, 2011 #2

    rock.freak667

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    Homework Helper

    It's just the gravitational force between two point masses. The gravitational force is equal and opposite on each mass.

    If you have three masses, you'd need to apply more rules with the formula to get the resultant force.
     
  4. Nov 12, 2011 #3
    Ok thank you.
    Maybe you can help with this question as well...

    During a jump off a diving board, is your apparent
    weight (a) equal to your true weight, (b) slightly less
    than your true weight, (c) slightly more than your true
    weight, or (d) zero?

    The answer is zero? I thought it would have been (b)
     
  5. Nov 12, 2011 #4
    Last question... what is the equation...

    F is proportional to m/r^2
     
  6. Nov 12, 2011 #5
    Actually one last question also... Why do we use the gravitational constant G?
    Is this only relevant to earth? therefore if I wanted to calculate the gravitational force of an object to mercury I would have to use another value that is not G?
     
  7. Nov 12, 2011 #6

    DaveC426913

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    Why do you think it would have been b?

    If you held a bathroom scale against your feet during your jump, what do you think the scale would show as your weight?
     
  8. Nov 12, 2011 #7

    rock.freak667

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    G is a universal constant, so in any calculation with that formula you'd use one value of G.
     
  9. Nov 12, 2011 #8
    Zero... but that's because you don't have the natural force of the ground to push up on the scale, which in return determines the weight....

    But I also know w = mg.... and you have to have some initial acceleration greater than g and NOT zero to move upward... there for weight would exist..... would it not?
     
  10. Nov 12, 2011 #9
    So if I was listening to my self I should have actually said the weight would stay the same.
     
  11. Nov 13, 2011 #10

    DaveC426913

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    Gold Member

    Weight is what a scale measures. It measures the force placed upon it. On the moon you would weigh less.

    How much would you weigh in space, if you pressed the scale against your feet? (What would keep the scale pressed against your feet if you let go of it?)

    How much would you weigh if you pressed it against your feet while suspended in midair (after you've left the ground)?
     
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