Q1:
Why shouldn't be the loop of real roller coasters be round in
shape? Why must it be elliptical in order not to hurt the
riders?
Q2:
Must the starting point be higher then the top of the loop, so
that there is enough energy for the coaster to complete it?
Q3:
Is there any factors limiting the no. of carts in a coaster
train?
Concerning question #2.
This is my shortest answer ever. Yes.
About question #3.
One obvious limitation is that the train of cars must be shorter
than the total roller coaster track. It is also best to have the
train short compared to the size of any of the features (hills,
curves loops, etc) of the track so that the changes in
acceleration which cause the excitement are not moderated by
having part of the train rising while another part is falling. I
suspect a more restrictive limiting factor is keeping the total
mass of the train to a minimum to limit the forces induced by the
accelerations the train experiences.
I wish you Happy Lunar New Year & Kung Hei Fat Choi as well.
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JDJ