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Homework Help: Question: Why this ?

  1. Nov 18, 2005 #1

    How are you friends ?

    I want to know why when I let fall tow things that have a different mass, why they reach the ground in the same time?

    Thank you for your time.
  2. jcsd
  3. Nov 18, 2005 #2
    Newtons F = m*a and the approximation F = m*g, so a = g

    Although I guess if you really want to be anal, the heavier object hits very slightly first because the earth is accelerating up to the heavier object. So two earth sized masses would fall toward each other faster than a ping pong ball and the earth.
  4. Nov 18, 2005 #3
    The equation of gravitational law shows it
    F = GMm/r^2 where F is force applied due to gravitation by earth, G is a constant, M is the mass of the earth, m is the mass of the thrown object and r is the radius of the earth and from the law distancebetween the centre of two objects.

    F = ma
    therefore a = F/m = which here is g.
    thus g is equal for all objects. may it be anything. now what mcah5 explained is the gravitational force applied by object on earth. the heavy celestial bodies apply gavitational force on earth due to which the gravitational force on earth due to object becomes negligible.
  5. Nov 18, 2005 #4


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    Gold Member

    OK, now that the 'how' has been answered with equations, perhaps we can answer the 'why'? i.e a more intuitive answer.

    I respond to your question with another question:
    Tell me why you think they wouldn't they hit the ground at the same time.
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