Safety on the Roller Coaster
Test pilots and astronauts experience lots of accelerations during their job performance. To prepare for this, they all go through physical training to see how much acceleration they can endure without getting sick or becoming unconscious. Experiencing an acceleration of more than nine times gravity for a sustained period will cause unconsciousness in most people. Since the acceleration due to gravity is 9.8 m/s² or approximately 10 m/s² , you can refer to other accelerations in terms of 1 g.

An acceleration of 2 g is approximately 20 m/s² while an acceleration of 8 g is approximately 80 m/s². Astronauts sometimes experience as much as 6 g's during liftoff.

Safety on a roller coaster requires that you stay below 4 g for the entire ride. You must never go beyond 4 g for even a short time. Changes in small accelerations may make a better ride than one big thrill from a single large acceleration.