why doesn't a looping roller coaster fall off its track?

Question

i have got a holiday homeork in which i have to solve a crossword but there's a question whose answer i do not know ... please tell me what it is ....
the question is" Because of ________ a looping roller coaster will not fly off the track "
(centrifugal force doesn't fit in the crossword )

Answer 1

because when the roller coaster enters the loop the weight of coaster provide a centripetal force which keep it going in circular motion

Answer 2

Rails? If you look closely to roller coasters, they are actually clamped pretty tightly to the rails so that even if something goes wrong and the centrifugal force is not enough, the cars will still stay on the track.

Answer 3

Physics.

Answer 4

centripetal force

Answer 5

momentum?