   Given a Collision Normal in 3D, how to calculate the new Trajectory?
  One of the objects has infinite Mass. It's like a wall, but may be orientated in any 3D direction.The other Object is a Ball. For simplification I just want to reflect the Ball trajectory on the wall, no speed is lost.So given Ball Velocity (Vx, Vy, Vz) and Wall normal (Nx, Ny, Nz)what is the new Ball Velocity?   
  A quick google came up with an article that seems exactly what you want: here.BTW: If you can, forget about Vx, Vy, Vz, etc. and just think about V. What's so great about vectors is you can ignore their components.   ;  Compute the velocity in the normal direction:float normalVelMag = DotProduct( normal, velocity );Determine if we're moving towards collision:if( normalVelMag > 0 ) return; //moving away from collisionCompute delta velocity:Vec normalVel = normal * normalVelMag;float coefRestitution = 1.0f; //0 would slide along plane, 1 reflectsVec deltaVel = normalVel * -(1 + coefRestitution);Compute resultant velocity:velocity += deltaVel;Putting it all together:float normalVelMag = DotProduct( normal, velocity );if( normalVelMag < 0 ) velocity += normal * normalVelMag * (-1 - coefResititution);Long winded example: http://www.gamedev.net/community/forums/viewreply.asp?ID=3549796</a?;  what you want to do is called refecting. You reflect vector A against a normal vector N.float m = dot(A, N);vec B = N * m * 2;vec C = A - B;C is your new velocity vector   