   question about moving sphere vs edge intersection.
  Please look at page 17 below PDF. http://www.peroxide.dk/papers/collision/collision.pdfThe page has written this equation. A = |edge|^2 * -|velocity|^2 + Dot(edge,velocity)^2B = |edge|^2 * 2(Dot(velocity,baseToVertex)) - 2((Dot(edge,velocity) * Dot(edge,baseToVertex))C = |edge|^2 * (1-|baseToVertex|^2) + Dot(edge,baseToVertex)^2However, there is no basic equation.anyone know it?   
  See equation 3.5 on page 15.   ;  thank you for reply ToohrVyk.but, I know ax^2+bx+c. I am looking for the equation to which A, B, and C of p17 are obtained. How can I derive the expression of A, B, and C?;  Well it seems to me you have to do collision between a moving sphere and the edge of the triangle. The basic concept here is to treat the collision not as a sphere to edge collision but as a ray to cylinder collision. So if you want to find the intersection between a ray and a collision you must right down the equations of the ray and the cylinder:Ray: P(t) = Origin + Dir * t;Cylinder: |((P-V1)xE)^2| = Radius^2, where P is a point on the surface of the cylinder, and V1 is the first vertex in the edge that forms the cylinder's axis.By plugging Origin + Dir * t in the cylinder's equation you get a quadratic equation.   ;  thank you Deliverance.i think i understood now.i couldn't have done it with out you. thanks.