gravity on a slope

[kade]

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?

 

 

[timo]

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

[kade]

okay ill try it

 

How should I go about testing this?

[swansont]

Rolling is different than falling, because rotation is involved

 

http://blogs.scienceforums.net/swansont/archives/2066

[timo]

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.

[Mr Skeptic]

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.

[mathias]

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.

[swansont]

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.

[kade]

thank you for all the replies but I am not smart enough in this subject to know what you are talking about

[swansont]

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.