You don't indicate where you live so I don't know if you're near any parks or whether they're open now. if you could get to a few parks before your project is due, you could do a pulse-heartbeat experiment. Buy one of those handheld blood monitoring instruments, about the size of a paperback novel. Take readings while you climb the lift hill. Then take readings immediately after you get off. See if and how much the coaster increases your pulse and systolic/diastolic blood pressure. Try to use a group, preferably including a girl, teenager, someone in his or her 20s and someone in his or her 50s or 60s. Do Coasters affect anyone ? Males more than females ? Older people more ? How long does it take to recover from the effects (1 min., 3 min., 5 min., 10 min., etc.) If you had time, you could explore various aspects of this. Does keeping one's eyes closed reduce the effect ? Does speed, inversion, height, etc., increase the effect ?
Such a study would be (l) original, (2) scientific, (3) "clean," that is, it isolates the variables with no unwanted factors, (4) easily quantifiable, and (5) repeatable by someone else at another time. It thus would meet all requirements of national and international science fair competitions.