Roller
coasters today employ clothoid loops rather than the circular loops of earlier
roller coasters. This is because circular
loops require greater entry speeds to complete the loop. The greater entry speeds subject passengers
to greater centripetal acceleration through the lower half of the loop,
therefore greater G’s. If the radius is
reduced at the top of the loop, the centripetal acceleration is increased
sufficiently to keep the passengers and the train from slowing too much as they
move through the loop. A large radius
is kept through the bottom half of the loop, thereby reducing the centripetal
acceleration and the G’s acting on the passengers.