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# ball falling & spinning: what's the next velocity after collision?

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is there any knowledgable person out there who can point me out to some info on how i could realistically calculate the impulse of the collision when a spinning ball collides with a plane (linear and angular velocities together with coefficient of friction and restitution need to be considered). We could take the simplistic case in 2d, its better for explaining i guess. please help me

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Someone might be able to realistically calculate it for you if they were to know a little more than just a "ball." Is it a billiard ball, ping pong ball, bowling ball, etc. You can''t realistically calculate it without knowing the mass and all that other fun stuff. Give a little more specific information.

-UltimaX-

"You wished for a white christmas... Now go shovel your wishes!"

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i just want the formulae... irrispective of what is the mass and properties of the ball and what not. I would like to change the mass, and coefficient of friction and restitution when i''m defining the feel of the game i''ll be doing.

specifically i would like if someone knew how to calculate that in the impulse J.
Right now i''m trying to calculate the impulse J, with which i modify the velocity. After this i calculate the frictional impulse (if u can call it so), where i take into consideration the tangent velocity (including the angular velocity of course), and the coefficient of friction. With this impulse i calculate again the new velocity and new angular velocity

This doesn''t produce realistic results when i use a coefficient of friction greater than 0.2. The angular velocities seems to give too much push to the ball :S

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you have the coeff of restitution which is how much bounce the collision has, you have static and dynamic friction coeffs that decide how fast the collision makes the ball spin due to friction(using the relative velocity of the point of contact on the ball and the plane). friction only acts perpendicular to the contact normal and opposite the direction of the velocity. restituition only acts along the normal.

hope that helps

fusi0n

"We are what we repeatedly do. Excellence, then, is not an act, but a habit." - Aristotle

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hi fusion,
thanks for your reply. I already got something working but its not realistic in the sense that the rotation due to friction is giving too much of a push. Imagine a rubber ball spinning, but its gaining too much (unrealistic) speed when it touches the floor. So if its colliding with a V structure (in 2d) it never stops since it starts climbing a bit the line before it falls back.

maybe there''s someone who already has the formulae for calculating the impulses properly . And they wish to share their wisdom *hint hint* :D

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Ok, I''ll give it a try:

A)The plane, do you consider it fixed somehow? Or does it have degrees of freedom > 0?
Let''s assume it can''t rotate and that it can''t move => 0 degrees of freedom.
B)If you use the conservation of energy principle AND assume that neither ball nor plane will be destroyed (or have their shape altered) your ball will _always_ jump off! (Totally elastic collison combined with A)
C)Friction is something "dirty", it''s something that takes "useful"/mechanical energy and produces heat, so using B will be a pain.

Well...
The only thing I can make out of it is that you shouldn''t use conservation of mechanical energy as a start...

/Ola

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http://www.cs.unc.edu/~ehmann/RigidTutorial/

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