1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gravity independant of mass?

  1. Apr 25, 2009 #1
    Following text:

    "Galileo Galilei is supposedly the first one to prove that the speed of a falling
    object is independent of its mass. He did this by demonstrating that a 100 pound
    cannonball and a one pound ball dropped at the same time from the Leaning
    Tower of Pisa reached the ground at the same time. The acceleration of gravity
    is therefore independent of mass."

    I have never really understood why it hits the floor at the same time. When I look at the formula F = mg, I would say the force of gravity is greater for the 100 pound ball, so why does it not fall faster? Let's also assume that it's performed in vacuum.
  2. jcsd
  3. Apr 25, 2009 #2
    you've got that equation right.


    With F Being the force of gravity on the object. However, the 100 pound ball is harder to accelerrate than the 1 pound ball. That can be expressed as


    Where F is the force on the object, and a is the acceleration of the object. All you must do is set these forces equal to each other.


    divide by m.


    So any object, neglecting air resistance will fall with an accleration of g under earth's gravity.
  4. Apr 25, 2009 #3
    Thanks, I fully understand now.
  5. Apr 25, 2009 #4
    But considering air resistance, shouldn't the cannonball in Galileo's story reach the ground first? Did they modify the story or wasn't it noticeable?
  6. Apr 25, 2009 #5
    It probably wasn't noticeable, but as far as I know the "Leaning Tower of Pisa Stories" are entirely fictitious, and the experiments were actually performed using angled ramps to the same effect, but reducing the impact of air resistance.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook