All About G-Forces

           A roller coaster designer’s main goal is to produce as many safe accelerations on the rider’s body as possible. If you're travelling at a certain speed, and not shifting, you can't feel it, just like you can’t feel the rotation of the Earth, despite the large rate at which we are spinning. Humans can't feel speed; we can only feel or sense acceleration.
           G loading is expressed as a ratio of the force developed in changing speed or direction relative to the force felt due to the earth’s gravity. The smaller the curve radius and the higher the speed, the higher the g force. Thus, a 2g force on a 100 pound body causes it to weigh 200 pounds. Race car drivers in the Indianapolis 500 are subjected to more than 3g’s in the corners and there are loop coasters that subject passengers to as much as 5g’s.

Not all g forces increase the weight of the passenger. As a vehicle goes over the top of a hill the load on the passenger becomes less than earth’s gravity and, in the extreme, could throw an unrestrained passenger out of the car. Some coasters do subject passengers to slightly negative g’s which cause them to raise off their seats and become “weightless” for a short period. This is often a desirable feature. Coasters with numerous airtime moments often rank among the best in the world.

Restraint design is directly affected by the g-forces felt during the ride. ASTM standards recommend types of restraints based on the range of g-forces. If all rides were geared to the weakest among the population, there would be no rides. The more safe accelerations on a ride the better.