1. The problem statement, all variables and given/known data In the normal loop the loop problem involving rotational energy where the marble goes down the hill and goes through a loop the loop, it asks for the minimum height of the hill to keep the marble on the track. 2. Relevant equations But why does the normal force have to equal 0? 3. The attempt at a solution I just dont know. How do we factor the idea that the marble doesnt fall off into the problem?