At the top of a loop (radius R): N + mg = $mv^2$/R => N = $mv^2$/R - mg Apparent weight = N. Weightlessness when N = 0 => v = sqrt(gR).

At the bottom of a loop: N - mg = $mv^2$/R => N = $mv^2$/R + mg Apparent weight is always greater than real weight at the bottom.

On a hill crest: N = mg - $mv^2$/R. Leaves the surface when v = sqrt(gR).

In a valley: N = mg + $mv^2$/R. Always pressed into the seat.