Why Must the Normal Force Equal Zero at the Top of a Loop?

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SUMMARY

The discussion centers on the physics problem of determining the minimum height required for a marble to complete a loop-the-loop without falling off. It concludes that the normal force at the top of the loop must equal zero to ensure the marble remains on the track. If the normal force were greater than zero, a lower initial height could suffice, contradicting the requirement for the minimum height. Thus, zero is established as the only viable option for the normal force at the loop's apex.

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Brett R.
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Homework Statement


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.

Homework Equations


But why does the normal force have to equal 0?

The Attempt at a Solution


I just don't know. How do we factor the idea that the marble doesn't fall off into the problem?
 
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Brett R. said:
But why does the normal force have to equal 0?
The normal force cannot be negative, agreed?
You are looking for the minimum initial height for it to stay on track. If the normal force at the top were greater than zero then a lower initial height could have been used.
Zero is the only remaining possibility.
 
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