Modern roller coasters are works of engineering art. Every heart-pounding ascent and stomach-dropping plunge is calculated to deliver precise jolts of fear, panic and ecstasy. But every so often, the squeeze of a corkscrew or the weightlessness of a steep drop is a little too much for the pile of nacho cheese fries churning in your belly, and before you can say, "Look out below!" you blow.
Why do roller coasters wreak havoc with our digestive tract? It's all about G-forces. The "G" stands for gravity, with 1G representing the normal pull of gravity that we experience every day. Roller coasters use acceleration, momentum and quick changes of direction to produce both positive and negative G-forces.
Positive G-forces create that face-flattening feeling that you experience at the bottom of a steep hill, when it's nearly impossible to keep your hands raised in the air. Negative G-forces (anything less than1G) produce those weightless moments, when you lift momentarily out of your seat and your stomach momentarily lodges in your throat [source: Berkowitz].
Why do some people puke on roller coasters and others don't? It might have to do with the gastro esophageal valve, the one-way muscle that transfers food from the esophagus to the stomach. In some folks, the negative G-forces experiences on roller coasters are strong enough to make that one-way valve a temporarily two-way street [source: Berkowitz]. Lovely.