# Q & A: Is car mass or track height more important for a good roller coaster?

Q:
What has a greater impact on the function of a roller-coaster. The height of the first hill or the mass of the actual car? Since PE=mgh doubling either the mass or height should result in identical increase in PE. If the height of the first hill is already the highest on the track, but the car still doesn't make it up the second hill could this problem be solved by either increasing mass of car or increasing height of hill? Since mass relates to inertia of object would the problem most probably be not enough inertia (Newton Law 1). Could you invent a roller coaster that is made of two parts, one part contains a large mass that disconnects from the coaster at the bottom of the first hill enabling the cart to go over an even higher second hill. Sorry that this is a long question, I just like roller coasters and applied physics. Thanks, Tyler
- Tyler (age 18)
Columbus, OH, USA
A:

Actually, just going by simple energy conversion, the mass of the car has no effect at all! While it's true that increasing mass does increase potential energy (PE=mgh), we must also remember that the kinetic energy of the car depends on mass as well (KE=mv2/2). That means making a car more massive also makes it harder to move, and it won't be able to go as fast! Even having a detachable mass wouldn't work, because when the mass breaks off from the car, it also takes its kinetic energy with it, meaning that the car gets nothing out of the deal. Making the first hill taller, however, will improve your roller coaster and allow your car to go over the second hill.

Matt Z.

p.s. There might be a little effect of mass when you take into account air friction, but the basics are just what Matt said./ mw

(published on 01/20/2015)