This Wednesday, we had a small committee meeting at Six Flags America in southern Maryland. The meeting agenda included a break in the afternoon to do some "classical mechanics research" (including pulling 3 Gs on a roller coaster) which I now present to you!
The research included wearing a vest on roller coaster rides that measured our change in altitude and the g-forces we encountered. A device, called an accelerometer, tucked in the vest actually did the measurements, recording our accelerations left and right, up and down, forward and backward as well as charting our changes in height above the ground.
Look at the bottom graph above for the Superman roller coaster which has a near-vertical drop from 205 feet. Around the 90 second mark, you'll see the red line showing the change in altitude as we dropped from 20 stories high back down to ground level.
In the top Superman graph, you can see our acceleration in the Y-axis, up and down relative to the body, represented by the orange line. As we rounded the top of the climb, our acceleration dipped below zero since we were slowing down (showing negative acceleration). As we went into the drop and picked up speed, it rose quickly until we reached our maximum acceleration at the bottom of the hill.
We know that we should have experienced around 3 Gs on the Superman ride, and we can use our data to prove that we did. G-force (the "g" comes from "gravity") is actually not a force but a measure of acceleration - the acceleration of an object (like a roller coaster rider) relative to a free fall.
An object dropped on the Earth will accelerate at 9.8 meters per second squared thanks to the force of gravity. Hence, 9.8 meters per second squared is 1 G. When we stand on our bathroom scale, we weigh ourselves at 1 G.
Once we start accelerating faster than 9.8 meters per second squared, though, it's as though gravity is stacking up on top of us. In the example of the Superman roller coaster, at the bottom of the drop, we are near our maximum acceleration of 33 meters per second squared.
Dividing 33 by 9.8 meters per second squared, we get 3.4, which means we pulled 3.4 G on the Superman ride. Because gravity felt over three times as strong, it also felt like we weighed over three times as much.
Look at the following graphs and try to guess what kind of ride gave us this data:
Looking at the red altitude line, you can see that we had a slow increase in height up to a maximum and then a sudden decrease in height. The orange 'acceleration in the Y-axis' line shows us that our acceleration was relatively steady until just before our big loss in altitude. Then, as we neared the ground, we had a huge increase in acceleration.
Did you guess? This data is from the Tower of Doom vertical drop. Incidentally, if you look at the acceleration in Y graph, you'll see that before and after the action the line is holding steady around 9.8 meters per second squared. This is because the force of gravity is always acting on us!
If you're interested in collecting your own Six Flags physics data, keep an eye out for Physics Day at a Six Flags near you. Click here for photos and info from this year's Physics Day at Six Flags America. Oh, and if you wear an accelerometer vest at the Six Flags America Physics Day, you'll get free passes to jump to the front of the line!