Rolling ball on an incline
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Rolling ball on an incline
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c_plus_plus
My Face Hertz


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Joined: 30 Jan 2006
Posts: 575
Posted: 30 May 2006 08:30:25 pm    Post subject:
how is the acceleration of a ball rolling down an incline implemented? I'm wondering this so I can start experementing with physics engines (BASIC and elsewhere)
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bukwirm


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Joined: 06 Dec 2005
Posts: 233
Posted: 30 May 2006 08:42:32 pm    Post subject:
Have you taken any Physics classes? If so, how many / which ones?

How accurate do you want the calculations to be? Do you want to account for friction, rotational inertia, etc.?

A block sliding down an incline is a lot easier.

Last edited by Guest on 30 May 2006 08:43:20 pm; edited 1 time in total
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c_plus_plus
My Face Hertz


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Joined: 30 Jan 2006
Posts: 575
Posted: 30 May 2006 08:52:59 pm    Post subject:
I have taken no physics classes but I understand concepts like velocety, acceleration, force, ect. It would be nice to include the specifics. Im not sure about the ball, but that is what I want to have move and thus the phisics should probably fallow a ball instead of a block.
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Liazon
title goes here


Bandwidth Hog


Joined: 01 Nov 2005
Posts: 2007
Posted: 30 May 2006 08:55:45 pm    Post subject:
code design specifics would be really helpful for me too.
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bukwirm


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Joined: 06 Dec 2005
Posts: 233
Posted: 30 May 2006 08:59:55 pm    Post subject:
Well, the acceleration for a block sliding down a ramp is:

a = g * (sin(theta) - u * cos(theta))

where a is acceleration, theta is the angle of the ramp, and u is the coefficent of friction.
For the ball, you'll have to give me a little time to find my physics book.

Edit: g is the acceleration of gravity.

Last edited by Guest on 31 May 2006 08:46:17 pm; edited 1 time in total
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c_plus_plus
My Face Hertz


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Joined: 30 Jan 2006
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Posted: 31 May 2006 08:14:12 pm    Post subject:
did you find your phisics book yet?
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bukwirm


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Joined: 06 Dec 2005
Posts: 233
Posted: 31 May 2006 08:45:46 pm    Post subject:
Can't find my book, had to borrow my brother's.

For a ball with no rolling resistance, acceleration is given by:

a = 5/7 * g * sin(theta)

where a is acceleration, g is the acceleration due to gravity, and theta is the angle the ramp makes with the horizontal.

Last edited by Guest on 31 May 2006 09:12:15 pm; edited 1 time in total
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DarkerLine
ceci n'est pas une |


Super Elite (Last Title)


Joined: 04 Nov 2003
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Posted: 31 May 2006 08:55:26 pm    Post subject:
Same thing except for no friction?
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bukwirm


Member


Joined: 06 Dec 2005
Posts: 233
Posted: 31 May 2006 09:01:25 pm    Post subject:
No, I left something out. I'll fix it in a minute.

Fixed! See previous post.

Last edited by Guest on 31 May 2006 09:11:50 pm; edited 1 time in total
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Fr0stbyte124


Advanced Newbie


Joined: 26 Jan 2006
Posts: 98
Posted: 07 Jun 2006 05:24:46 pm    Post subject:
Another interesting property is this: disregarding friction and centrifugal resistance, the (net) velocity of the ball will always be the same at a specific height, regardless of the incline.


Quote:
a = 5/7 * g * sin(theta)

Where does the 5/7 come from?

Last edited by Guest on 07 Jun 2006 05:29:39 pm; edited 1 time in total
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DarkerLine
ceci n'est pas une |


Super Elite (Last Title)


Joined: 04 Nov 2003
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Posted: 07 Jun 2006 05:45:18 pm    Post subject:
It does seem rather arbitrary.
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axcho


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Joined: 09 Nov 2004
Posts: 555
Posted: 07 Jun 2006 06:21:21 pm    Post subject:
Quote:
Im not sure about the ball, but that is what I want to have move and thus the phisics should probably fallow a ball instead of a block.
Could you tell us what game you want to make involving a ball? I might be able to think of an easier way to implement the physics, depending on the specific game mechanics.
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bukwirm


Member


Joined: 06 Dec 2005
Posts: 233
Posted: 07 Jun 2006 06:45:30 pm    Post subject:
Fr0stbyte124 wrote:
Another interesting property is this: disregarding friction and centrifugal resistance, the (net) velocity of the ball will always be the same at a specific height, regardless of the incline.


Quote:
a = 5/7 * g * sin(theta)

Where does the 5/7 come from?
[post="81781"]<{POST_SNAPBACK}>[/post]

The moment of inertia of a solid sphere, unless I made a calculation mistake.
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Fr0stbyte124


Advanced Newbie


Joined: 26 Jan 2006
Posts: 98
Posted: 07 Jun 2006 07:16:11 pm    Post subject:
The moment of inertia for a solid sphere is 2/5*mr^2. And before we make things that complicated, we should probably find out what c_plus_plus has in mind.
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