Hello, When doing simple physics problems involving roller coasters, I'm having trouble finding the centripetal force/acceleration. When the object is at the bottom of the loop, I understand the centripetal acceleration relies on the normal force. However, when the object is at the top of the loop, why does it also rely on the normal force? Doesn't the gravity vector and normal vector point in the same direction? Please help, I am completely confused, and can't find any good explanations on this for intuition on the internet. Thanks.