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Weight of the whole earth with reference to an apple

  1. Jan 1, 2008 #1
    I don't know the answer to this question but it may only require common sense:

    Let's say an apple on the surface of the earth weighs 0.25 Kg. Imagine the apple as the little earth and the whole earth on top of it. What is the weight of the earth with reference to that apple?

    I suspect the answer is 0.25 Kg also? If so, why? If not, then what is the correct answer and why?
  2. jcsd
  3. Jan 1, 2008 #2


    Staff: Mentor

    First kg is a unit of mass, and weight is a force. So a .25 kg apple in earth's gravitational field would weigh 2.45 N. Since forces are equal and opposite (Newton's 3rd law) the weight of the earth in the gravitational field of the apple would also be 2.45 N.
    Last edited: Jan 1, 2008
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