Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why roller coaster loops aren’t circular anymore

vox.com

Post reply on HN
Print view View original

41–50 of 110 posts

Re: Why roller coaster loops aren’t circular anymore

#41

Post by tetris11 »

mgdlbp wrote: post #22
tobtoh wrote: post #18

If I remember my uni engineering/calculus maths class correctly, the third derivative of position is used in planning these sort of curves. The first derivative of postion (with respect to time) is velocity. The second derivative is acceleration (ie rate of change of velocity). And the third derivative is jerk (rate of change of acceleration). And 'jerk' has to be kept below a certain threshold for humans to find mov…

Also seen in the planning of curves in roads (where jerk corresponds to the rate at which a steering wheel must be turned) and railways. And this is also why the passengers jerk of a vehicle jerk backwards after it comes to a complete stop. Their muscles statically counter the relative forwards acceleration of their torsos during braking and require time to react to the acceleration suddenly going away. This effect c…

Given that train drivers have cameras pointing at passengers, I'd argue that they are indeed aware of the effect, but don't always roll the stop due to delays on the line and/or personal reasons.

Re: Why roller coaster loops aren’t circular anymore

#43

Post by kazinator »

A "G force spikes" is called a "jerk" in physics; as acceleration is the rate of change of speed, jerk is the rate of change of acceleration. The jerk is huge in transitioning from a straight track to a circular one immediately, since the acceleration goes from zero to nonzero instantly.

Re: Why roller coaster loops aren’t circular anymore

#44

Post by 2143 »

WalterBright wrote: post #24
mgdlbp wrote: post #22

Earlier quoted context omitted.

Also seen in the planning of curves in roads (where jerk corresponds to the rate at which a steering wheel must be turned) and railways. And this is also why the passengers jerk of a vehicle jerk backwards after it comes to a complete stop. Their muscles statically counter the relative forwards acceleration of their torsos during braking and require time to react to the acceleration suddenly going away. This effect c…

> but few drivers or rapid transit systems seem to be aware I find that amazing. What the heck are drivers ed instructors doing? It's not just hard on the passengers, it's hard on the machinery. It's the same with the clutch. I've driven with enough people who fancy themselves as great shifters, but they jerk the hell out of the clutch every time, never attempting to match the shaft speed with the engine speed. If I…

"They way somebody treats their car is the way they treats themselves" — Frank Martin (paraphrased for gender neutrality).

And you can tell how somebody treats their car by examining how long the clutch lasts, if they drive a manual.

Re: Why roller coaster loops aren’t circular anymore

#45

Post by kimburgess »

tobtoh wrote: post #18

If I remember my uni engineering/calculus maths class correctly, the third derivative of position is used in planning these sort of curves. The first derivative of postion (with respect to time) is velocity. The second derivative is acceleration (ie rate of change of velocity). And the third derivative is jerk (rate of change of acceleration). And 'jerk' has to be kept below a certain threshold for humans to find mov…

This video has an excellent visual demo of that concept: https://youtu.be/aVwxzDHniEw?t=451.

Re: Why roller coaster loops aren’t circular anymore

#46

Post by atoav »

tobtoh wrote: post #18

If I remember my uni engineering/calculus maths class correctly, the third derivative of position is used in planning these sort of curves. The first derivative of postion (with respect to time) is velocity. The second derivative is acceleration (ie rate of change of velocity). And the third derivative is jerk (rate of change of acceleration). And 'jerk' has to be kept below a certain threshold for humans to find mov…

A very similar thing is done in the creation of reflective surfaces on car bodies (typically in CAD software).

They call these constraints by G and a number.

  G1 would be a positional constraint: the two surfaces meet each other at the same point
  
  G2 tangential: same as G1, but the surfaces are tangential
  
  G3: same as G2, but the curvature (radius^-1) of the surfaces is the same at the point where the two meet. This essentially means the curvature combs of the surfaces shall meet at the same position (G1)
  
  G4: same as G3, only now the meeting curvature combs have to be tangential as well
  
  G5: same as G4, only now the curvature combs of the curvature combs have to meet at the same position
And so on. The goal is to create smooth transitions between two separate mathematical surfaces that cannot be seen in the reflections in the sheet metal. E.g. if you think about the connection of straight sheet of metal (curvature: 0) and a cylindrical surface (curvature: 1/radius) the curvature will go from zero to some different value immidiately on the transation you will definitly see this as a hard corner on the reflection or when light falls onto the surface.

Re: Why roller coaster loops aren’t circular anymore

#47

Post by Gordonjcp »

mgdlbp wrote: post #22
tobtoh wrote: post #18

If I remember my uni engineering/calculus maths class correctly, the third derivative of position is used in planning these sort of curves. The first derivative of postion (with respect to time) is velocity. The second derivative is acceleration (ie rate of change of velocity). And the third derivative is jerk (rate of change of acceleration). And 'jerk' has to be kept below a certain threshold for humans to find mov…

Also seen in the planning of curves in roads (where jerk corresponds to the rate at which a steering wheel must be turned) and railways. And this is also why the passengers jerk of a vehicle jerk backwards after it comes to a complete stop. Their muscles statically counter the relative forwards acceleration of their torsos during braking and require time to react to the acceleration suddenly going away. This effect c…

> This effect can be prevented by gradually letting off the brake before reapplying it fully upon stopping, but few drivers and rapid transit systems seem to be aware.

Is this why it seems to be mostly Americans that are into the idea of self-driving cars, because the standard of driving is so low?

Re: Why roller coaster loops aren’t circular anymore

#48

Post by thereisnospork »

SV_BubbleTime wrote: post #39
mc32 wrote: post #8

Earlier quoted context omitted.

Also by the time you get to the apex it’s going slower than when it entered the loop.

I’m having trouble imagining a scenario where this is not the case.

Here's a 1 reasonable and 1 contrived example:

An inverted loop, where the loop is lower than the track, and with a very long train, where the center of mass continues to decrease in height due to the part of the train not presently looping.

Re: Why roller coaster loops aren’t circular anymore

#49

Post by TylerE »

mixmastamyk wrote: post #42

I remember the Corkscrew at Knotts as a kid, no longer exists. The Revolution at Magic Mountain arrived in the late 70s with the new parabolic shape and still running. (Southern California)

It does actually. It was moved to Silverwood in Idaho and has operated there very since.

Re: Why roller coaster loops aren’t circular anymore

#50

Post by edejong »

jollybean wrote: post #13
akira2501 wrote: post #11

Earlier quoted context omitted.

If you're trading a horse for the car, a seatbelt might not be the first thing you'd think of. I don't think our views on danger have changed, it's just that any new technology requires a period of adjustment to it.

Our views have changed. We used to throw lawn darts, have fireworks, guns all over. Not even helmets on motorcycles. When I was a kid, we used to rid maybe 6 kids in the back of a pickup truck flat bed. That was normal . It would not only be illegal today, but probably considered very immoral. Hockey players didn't even wear helmets, not even the goalies (!). Nobody wore helmets when I grew up skiing, now almost ever…

We have a very substantial part of the population becoming chronically ill after an infection of a disease labeled “mostly mild”, yet we decided low-key interventions such as masking and air filtration are not worth it.
Post reply on HN