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Seperation effects on the forces of gravity and eletricity

  1. Feb 15, 2009 #1
    1. The problem statement, all variables and given/known data
    Two charged pellets are pulled apart to twice their original separation. (a) Which is likely to be larger, the gravitational force or the electrical force between them? Why? (b) Which will change by a greater factor when they are pulled apart, the gravitational force or the electrical force between them? Why?

    2. Relevant equations
    Fg = (G x m1 x m2) / r2
    Fe = (K x q1 x q2) / r2

    3. The attempt at a solution
    a) Well, assuming 6.673 × 10−11 for the constant of G and 8.987 x 10 9 for the constant of K, I would assume that the electrical force would be higher.
    b) I am assuming that they would change at the same factor when they are pulled apart.

    Am I assuming correct or am I wrong?
  2. jcsd
  3. Feb 15, 2009 #2
    gravitational force is immmmmmmensely SMALLER than the electrical force.

    remember, unless you are working with an extremely large mass, the electrical force will always be larger. plug in your value for mass and charge into the two force equations.
  4. Feb 15, 2009 #3


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    Homework Helper

    This type of question basically asks you what happens to the force when the distance is doubled. To see it, write
    Fe = (K x q1 x q2) / r2
    and then write it again replacing r with (2r). Do it with a red 2 if you can. Then you try to factor the 2 out so it sits in front of the rest of the stuff. In this case you'll get
    Fe2 = (K x q1 x q2) / (2r)2 = 1/2^2*(K x q1 x q2) / r2 = 1/4*Fe
    showing that the new force at double the distance is 1/4 of the original force.
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