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.