Flying Circus of Physics newsletter for May – July 2015
Data pubblicazione: 3-mag-2015
Flying Circus of Physics newsletter for May – July 2015
My new video series
My school (Cleveland State University) and I have started a new video series. Here is a link to the CSU YouTube channel where the first video has been posted. New videos will appear about once a month. If you want to subscribe to the channel so that you know when a new video has been posted, use the subscribe button. This first video shows me dipping my fingers into molten lead (about 750 degrees Fahrenheit).
www.youtube.com/channel/UChrOvC-DFkPNxKIxe-XKD3g
Fear and trembling at an amusement park
What is the attraction of amusement park rides? Well, a lot has to do with rotation because it involves strange forces that we rarely encounter in the everyday world except for when we take a fast turn in a car. In an amusement park, the rotations are much more rapid, creating accelerations of several gs (that is, several times the acceleration g due to gravity in a fall). You experience apparent centrifugal (outward) forces that threaten to either throw you from the ride or squash you onto a surface such as a seatback.
Of course, you can get those experiences on a tame merry-go-ride, but anyone older than a child (or rather, taller than a certain height restriction) wants something more complex and disorienting. The most common solution is for a ride to superimpose a secondary rotation of a short arm on a primary rotation of a long arm.
The two rotations might be in the same direction, in opposite directions, or even perpendicular to each other. If they are in the same direction, you experience the greatest centrifugal force and have the greatest speed when you are farthest from the center of the apparatus. If the two rotations are in opposite directions, your speed is least at the far point (due to the opposing rotations), but the force on you varies most rapidly there because you are being whipped through a highly curved path. To make the ride even scarier, the secondary rotation of the short arm might change abruptly, as can happen if the ride is tilted so that gravity can affect that rotation. Here are examples of superimposed rotations. (The first few minutes of the six minute video may be enough.)
www.youtube.com/watch?v=tuq1ff9kT-Y
Of course, roller coasters have long been popular because the height and speed provide an existential flirtation with death. But the roller coaster enthusiast long ago tired of simply riding up and down hills or even being inverted in spiral tracks. The existential flirtation now requires that death seem more imminent. Here for example, is a coaster that stops at the edge of a high region and then titters over that edge until the coaster’s section of track connects with the downhill section of track.
www.youtube.com/watch?v=aA4_BjmHzAM
At this point, a rider might be questioning if the mechanical engineer who designed the ride properly programmed the system for a good connection every time, before the coaster was released from the upper level of track.
Even more frightening is a coaster that gives the illusion that you will be launched into the sky and then gives the illusion that you are in free fall toward the ground. The current king of this type of coaster in Kingda Ka where you travel vertically straight up to reach the hill top and then travel vertically straight down to come down the other side. (Going straight up or straight down is scary but going up a steep incline while also inverted would be worse. Such coasters are now appearing in amusement parks.)
www.youtube.com/watch?v=7om9O0eXIpg
Many modern roller coasters are designed to produce large accelerations, up to 4 gs. However, such accelerations are not maintained because they can lead to loss of consciousness. One artist proposed a roller coaster whose only purpose is to kill the riders by sending them at high speed around the interior of many vertical loops, one after another. Because the head of the rider would be closer to the center of a loop than the feet, blood would tend to pool in the feet, leading to unconsciousness and then death. The proposal was, of course, not serious. (At least, I hope it was not serious.)
There are rides in which you really are launched, like a stone in a sling shot. In this next video, energy is stored in the stretched bands on the two sides of the passenger compartment (the stone). When the compartment is released from its catch point, the bands rapidly propel it upward. At this point, a rider might have some questions for the material science engineer who tested the strength of those bands, such as, how many stretching cycles can the bands undergo before failure is reached?
www.youtube.com/watch?v=a7fcM6ITjXY
Of course, if you really want to flirt with death, don’t bother with a coaster or even bungee jumping. Just jump from a great height and free fall.
www.youtube.com/watch?v=JjEsWj369rc
Here a person might wonder about the stability of the catching net. Is it anchored sufficiently? Does it stretch enough so that the person is decelerated safely? Can the staff repeatedly inspect an entire net for failure points, or do they just glance at it for big rips?
All these rides are designed carefully by engineers and scientists. However, here next is a ride in Russia that is so out of control that before I would ever get on it, I would want to see the design engineer’s physics exam grades. No, more than that, I would want the design engineer to be in the adjacent seat after he undergoes a current drug test.
I was horrified when I first watched this next video: outrageously dangerous rides, enough there to keep thousands of attorneys busy for years. But let me tell you that the video is a fake documentary. Listen for the dark humor hidden in the interviews with the design engineer. (This is as though Doctor Strangelove has begun designing amusement park rides.)
www.youtube.com/watch?v=RVeHxUVkW4w
Just remember: Physics is everywhere, especially at amusement parks where rapid rotations, abrupt changes in motion, great heights, inversions, and even falling are all fun (unless, of course, something goes wrong).
Cheers,
Jearl Walker
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