Find the minimum speed to make it through a loop: circular motion minimum speed in a loop problem.

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We compute the minimum speed to make it through a vertical loop by noting that normal force is minimized at the top of the loop, and if normal force goes to zero there, the object will only lose contact with the loop at that one instant.

For another example of how we use this result, here is a roller coaster with a rolling ball problem:

[juniorcyans]

Last Friday I solved this classical problem correctly using my own understanding. But your explanation helps me to understand better, especially how normal force works here.

[taniwha]

Very nice and concise explanation, thanks

[jesusparejopineda]

It's incorrect, actually v must be at least sqrt(5*g*r)