strange problem

Hi everybody! I''m creating a virtual billiard game. For this game, I use ODE and GLUT. I don''t know if you''ve heard of ODE, anyway it''s not important, because I don''t think the problem comes from it. I have this ball, rolling at a constant velocity: (velX, velY, velZ) In order to stop it, I apply on it a force whose values are opposed to the velocity: force(-velX*0.1, -velY*0.1, -velZ*0.1) This should slow down the ball. But when I read continuously the values of the velocity, it never slows down. But the force is here, I can read its values. Anyway, when I start clicking on the "render" window, magically, the ball starts slowing down. I''ve never seen such a thing. Any Idea? trust