I have two questions. when a car or roller coaster travels in a loop. At the top of the loop the forces that acts on the car are all downwards i.e. W and normal , so the net force is acting downward. I can't figure our any other force acting upward, so what actually will keep the car sticked to surface of the loop? Secondly, im confuse as when does the normal force diminish at the top of the loop. I have seen some animations which showed that normal force becomes smaller and smaller until it reaches at the top. But don't really know what is counter-force for the normal force. Something to do with cos component of W i guess, but not clear how cos they are in the same direction. English is not my first language so sorry for any mistakes.