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Question submitted by (16 July 1999)
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|I'm writing collision routines for a very simple game, and need to determine the outcome of a collision of two spherical objects, both of which are the same size. One of the objects will remain stationary, and the other is in motion. I have calculated the vector between the two objects, and have a vector of the direction of motion for the moving object. Is there an easy way to calculate the new direction of the moving object?|
let P be the point of contact on the stationary sphere. the vector
from the centre of this sphere toward P is PO. the tangent at P is
perpendicular to PO. also, suppose the direction of motion of
the moving sphere is labeled D.
the moving sphere will bounce away from P along the direction D' such that the angle between D and PO is the same as the angle between D' and PO.
extending D "into" the sphere and projecting the endpoint onto the tangent yields the vector XP, the component of D' parallel to the tangent.
of course, if the vectors D and PO are colinear, the moving sphere will simply bounce back in the direction of -kD where k is some constant.
Response provided by Hin Jang
This article was originally an entry in flipCode's Fountain of Knowledge, an open Question and Answer column that no longer exists.