Why Don't Roller Coasters Fly Off the Track?

Have you ever been on a roller coaster anddon't go off the tracks is that the curves and
wondered how the train stays on the track?turns are banked properly so that the gravitational
Have you ever watched a roller coaster andforce in combination with other forces acting on
thought to yourself, "Why don't the cars fly offthe train are balanced so that the wheels stay on
the tracks?"the tracks as a result of the sum of all the forces
If so, you're far from alone. There are severalacting on them.
explanations as to why roller coaster trains stayWhen a coaster does a loop and goes upside
on their tracks.down, the loops are specially designed to have
For one thing the wheel assemblies on their axlesthe tightest radius at the very top of the loop
go on both sides of each rail, so that they "hug"and to have much larger radii at the entrance and
the rails. But on top of the rails are the train'sexit of the loop. This gives roller coaster loops a
running wheels on which the train cars run. And ifshape very much like that of a regular helium
that weren't enough, the wheel assemblies haveballoon. Because of this shape of loop, the g
guide wheels in the middle of the assembly. Theseforces necessary to hold the train on the tracks
wheels help prevent lateral (side to side) motion.are low enough that the human body can
The guide wheels on wooden roller coasters arewithstand them without physical harm. But to be
on the insides of the rails. But on steel rails thesure, those g forces are strong enough to give
guide wheels might be either on the inside or thepeople quite a thrill!
outside.The "sticking power" that keeps roller coaster
And finally, there are special wheels underneathtrains on their rails can be mostly attributed to
the rails called upstop wheels that prevent thethe laws of physics - specifically the law of
trains from lifting off the rails.gravity.
But the most important reason roller coasters