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Treebeard's Stumper Answer
26 February 1999

Gee, Force!

We're off to Disneyland, yahoo! That's a theme park with many attractions, but I'm sure the longest lines will be at the roller coaster rides like Space Mountain and the classic Matterhorn. A big question with such rides is where to sit. Part of the thrill is the view, so the front is the place to be. But the biggest thrill is the g force we feel as the cars race around the track. So where's the best seat for maximum thrills: front, middle, or back? Or maybe it doesn't matter? After all, the cars are connected together, so they must all be going at the same speed.


Take the front seat of a roller coaster for the best view and the wind in your face. It's changes in speed and direction - acceleration - that we feel as force. Roller coaster cars are connected, so they must all be going the same speed. But they are in different places along the track. The front cars pass over the top of a hill and begin to gain speed downwards. This pulls the back car over the top at a higher speed. We can actually feel airtime as we are lifted from our seats against the restraining bar. For maximum force, the back seat is the place to be!

Notes:

I went through Disneyland with a small group of Dunn Middle School 6th graders. I figured the best way to enjoy the park is to stick with the youngest kids around, and carpe diem! There's an album of Disneyland photos from our school trip. The DMS kids were only interested in the new thrill rides, but I took them through a few old favorites, including the Treehouse and the Train Ride dioramas. The kids enjoyed them!

My father worked for the Carnation Milk Company, which still sells ice cream in the park. I first went to Disneyland as part of a company picnic in the mid-50s when it just opened and they still had E tickets. It's still fun, but the commercialism gets in the way. I grew up with Pacific Ocean Park (P.O.P) in Santa Monica and The Pike in Long Beach. These amusement parks sold rides, not a life-style.

I think the back seat of a roller coaster feels the greatest force as it's whipped over the hills. But what happens going down? If the situation is symmetrical, then maybe the front cars do better there? Graybear sends this analysis:

As the center of gravity of the trains goes downhill, speed increases. When maximum speed is attained, the front cars feel the greatest downward G-forces at the bottom. The rear cars are near maximum speed as they come over the hill, so the minimum downward (or, hopefully maximum upward!) G-forces are felt there.

I'm not sure that the front cars feel the greatest g-force on the downhill. It seems to me that it's actually the middle car (the center of gravity) that experiences the greatest speed downhill. But that's speed not acceleration. The rear cars still coming down push the front cars up the next hill, so the front cars are slowing down slower than they would by themselves. This also slows down the rear cars while they are still on the hill, so the rear cars must be slowing down faster. Since it's acceleration that we feel as force, doesn't this mean that the rear car is still the place to be?

Either way, everything happens much faster at the bottom of the hill. Any difference between front and back is less noticeable than at the top of the hill. And as David Sandborg points out on his Physics of Roller Coasters page, "It's probably harder to tell the difference between, say, 3.4 and 3.6 G's than it is to distinguish between -0.1 and 0.1 G's." I'll stick with my answer that the back seat is the place to be.

Graybear also reports on this fun variation:

The length of the train relative to the height of the hills makes a difference - short trains on long hills give a pretty constant thrill no matter what car you're in. The opposite situation is interresting - I was on a roller coaster once where the train was a little longer than the hill was tall. When I was in the front seat, the coaster slowed as I was heading down the hill, making me feel like I was going to tumble forward out. The front car reached the bottom just after the center of gravity was picking up speed. The effect greatly accelerated the car up the next hill - pretty wild!
I noticed the Disneyland rides have short trains, and they don't have big drops, at least compared to the nearby Six Flags Magic Mountain park. I'm sure this is because physical space is limited at Disneyland. They make up for it with quick turns and a jerky ride, as in the classic Mr. Toad's Wild Ride. This makes for big centripetal forces, but it's not always pleasant. I tweaked my neck on the Indiana Jones Temple of Doom ride, and it still hurts. I refuse to admit I'm old enough to heed the warning signs, so it must be the ride's fault!

We also did the new (for me) Star Tours ride, which is a moving platform/virtual reality ride based on the Star Wars movies. We sat in fixed seats watching a movie screen. The entire room moves to make it feel like we're moving with the screen. This was my first experience with a VR ride, and it really worked! I was most impressed when we went into hyperspace. The stars came together just like in the movies, and we felt a sustained push back for several seconds. How did they do that? I'm sure they tilted the whole room back on its end so we were pushed into our seats. I wish I'd been holding a pendulum!

There's an abundance of roller coaster info on the web, much more than I have time to read. Here are a few links I found for further study:

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