kade Posted August 14, 2010 Share Posted August 14, 2010 Okay, so I have been thinking about this for awhile. Gravity pulls everything down with the same air resistence at the same speed no matter the weight, correct? And gravity is what makes a ball roll down a slope. Then why when you get two balls with the same amount of friction, but different wieght, and you roll them down a hill, the one with more weight rolls down faster? Link to comment Share on other sites More sharing options...
timo Posted August 14, 2010 Share Posted August 14, 2010 (edited) Wasn't there some famous experiment by some famous scientist (Galileo?) proving that two balls heavy enough so that air resistance becomes negligible roll down the same speed? Perhaps you should simply try if they really roll down with different speeds. Seeing you are new: Welcome to sfn. Here's an alternative answer: If you [can] ignore resistance the two balls will roll down the slope with the same speed. That's what theory says. I was serious about trying it out, though. Edited August 14, 2010 by timo Link to comment Share on other sites More sharing options...
kade Posted August 14, 2010 Author Share Posted August 14, 2010 okay ill try it How should I go about testing this? Link to comment Share on other sites More sharing options...
swansont Posted August 14, 2010 Share Posted August 14, 2010 Rolling is different than falling, because rotation is involved http://blogs.scienceforums.net/swansont/archives/2066 1 Link to comment Share on other sites More sharing options...
timo Posted August 14, 2010 Share Posted August 14, 2010 Rolling is different than falling, because rotation is involved I was of course completely aware of that which is exactly why I proposed trying it out ok, I screwed that one up. Link to comment Share on other sites More sharing options...
Mr Skeptic Posted August 14, 2010 Share Posted August 14, 2010 Okay, so I have been thinking about this for awhile. Gravity pulls everything down with the same air resistence at the same speed no matter the weight, correct? And gravity is what makes a ball roll down a slope. Then why when you get two balls with the same amount of friction, but different wieght, and you roll them down a hill, the one with more weight rolls down faster? That will depend on their rotational inertia as well. And gravity does not pull at a "speed", it pulls at an acceleration. Link to comment Share on other sites More sharing options...
mathias Posted August 14, 2010 Share Posted August 14, 2010 Inertia will cancel out Mass. A lighter object will be falling with less Inertia. There is an equation that shows how inertia counters mass with free falling objects of different weights. Link to comment Share on other sites More sharing options...
swansont Posted August 15, 2010 Share Posted August 15, 2010 Inertia will cancel out Mass. A lighter object will be falling with less Inertia. There is an equation that shows how inertia counters mass with free falling objects of different weights. Again, rolling is different than falling. Rotational inertia depends on the mass distribution. Link to comment Share on other sites More sharing options...
kade Posted August 15, 2010 Author Share Posted August 15, 2010 thank you for all the replies but I am not smart enough in this subject to know what you are talking about Link to comment Share on other sites More sharing options...
swansont Posted August 15, 2010 Share Posted August 15, 2010 A rolling object has to divide its energy between translation and rotation, so it will move slower than an object that is only translating. Depending on the mass distribution, rolling objects can also roll at different speeds, e.g. a hollow object will roll slower than a uniform, solid object of the same mass. Link to comment Share on other sites More sharing options...
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