Normal force on top of a loop?

[lpbug]

Say we have a roller coaster, and we want to calculate the speed the roller coaster can go at barely making the loop. Normally, the equation would be n+w=m*v^2/r, but why do we set normal equal to zero when we're solving for the minimum speed? Where does the normal come from on top of the roller coaster anyway? Thank you all so much.

 

[gsal]

Hhhmmm...I am not sure I am following, but it seems to me that you already answered your own question.

What does the normal come from? It doesn't...that's why you set the normal to zero in the equation that you are solving, because if you want to calculate the point at which the roller coaster just makes it...well, at the point the coaster is "floating" and vertically stationary in midair as it is stopping from going up and getting ready to start coming down...

do I make sense?