I was practicing for one of my physics exams and there was a problem that asked for the minimum speed a rollercoaster would have to go for its riders to not fall out at the top of a loop. I did the problem but I'm having trouble understanding why the normal force here would be equal to zero. If they're supposed to stay in their seats, shouldn't there be a normal force on the riders by the seat?
[Physics] Why is the normal force equal to zero at the top of a rollercoaster if the speed is the minimum
kinematics
Best Answer
At minimum speed, at the top, the centrifugal force of the loop is equal to the centripetal force (gravity). So the upside down riders are neither pushed into the seat by centrifugal force, nor are they pulled down against the restraints by gravity, as at the correct speed these two forces equal, and cancel each other out, to essentially create a freefall effect. So there is 0 normal force between the seat and riders as they are in freefall with the seat.