# Free fall and Weight question

by musicboy
Tags: fall, free, weight
 P: 4 Hi there Just wondering: all objects fall at the same speed, right(not taking into account air resistance)? So if I dropped a feather and a bowling ball on the moon, they'd fall at the same speed. So far so good. But my physic book's definition of weight is "The weight of an object is the force that acts on it because of gravity; Weight = Mass x Acceleration due to gravity" . The bowling ball's mass is clearly greater than the feather's, so therefore it's weight and therefore pull of gravity on it must be different, resulting in a different speed.... Confused! Any help much appreciated :)
HW Helper
Thanks
P: 26,157
hi musicboy!
 Quote by musicboy … my physic book's definition of weight is "The weight of an object is the force that acts on it because of gravity; Weight = Mass x Acceleration due to gravity" . The bowling ball's mass is clearly greater than the feather's, so therefore it's weight and therefore pull of gravity on it must be different, resulting in a different speed....
yes, the force of gravity on it is greater (Mg > mg)

but force = mass times acceleration (that's Newton's second law),

so the accelerations are the same (A = Mg/M, a = mg/m)
P: 3,914
 Quote by musicboy Weight = Mass x Acceleration... The bowling ball's mass is clearly greater than the feather's, so therefore it's weight and therefore pull of gravity on it must be different,
You have the equation right there. If you change Weight & Mass by the same factor, Acceleration stays the same.

 Quote by musicboy resulting in a different speed....
The terminal speed, where air resistance = weight, is different. But in vacuum they fall the same.

 Sci Advisor Thanks P: 3,459 Free fall and Weight question To add to what A.T. And Tiny-Tim have said... There's an FAQ on this at http://www.physicsforums.com/forumdisplay.php?f=209
 P: 4 Gotcha :) Thanks very much all of you for quick and concise replies. Have a good day :D

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