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Why roller coaster loops aren’t circular anymore

vox.com

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Re: Why roller coaster loops aren’t circular anymore

#51

Post by irjustin »

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…

> What the heck are drivers ed instructors doing?

I mean to be completely fair - this is not their job. Driving instructors are there to keep everyone on the road safe - first.

Re: Why roller coaster loops aren’t circular anymore

#52

Post by yellowapple »

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…

> What the heck are drivers ed instructors doing?

Dinging me over their interpretations of ambiguous driving laws, if my experience is any indication.

Re: Why roller coaster loops aren’t circular anymore

#53

Post by therouwboat »

thrdbndndn wrote: post #31

I really want to like Vox's video format but just can't. Which is a shame because they have lots of topics that are quite interesting. I can't pin down which part that I hate most, the "stylish" presentation with random SFX and virtual pen circling around, or the fact they always insert some super low quality video conference footage instead of just letting the narrator paraphrasing (I get it they're the domain exper…

I couldn't watch it, I guess it felt messy and there was too much stuff going on, so it was hard to focus.

Re: Why roller coaster loops aren’t circular anymore

#54

Post by 9991 »

TylerE wrote: post #21
function_seven wrote: post #12

Earlier quoted context omitted.

You’re high. But also the photo was taken at an angle to the track, so it’s not gonna trace out a circle on your screen.

No, he’s not wrong. The exit is about 20 ft further forward than the entrance. A true circular loop the entrance and exit would be directly side by side.

That would be a helix, not a circle.

Re: Why roller coaster loops aren’t circular anymore

#55

Post by yccs27 »

cperciva wrote: post #33
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…

And 'jerk' has to be kept below a certain threshold for humans to find movement comfortable. It's not strictly a matter of threshold -- people might tolerate a higher jerk if it's for a much shorter duration, for example. In practice it doesn't much matter which metric you minimize; you'll end up with similar results. The simplest option is to minimize the mean absolute jerk, which has the side benefit of utterly con…

Note that 'mean absolute jerk' can also be described as 'total variation of acceleration over time'. That implies it does not depend on how fast the acceleration changes, only about the difference between minimum and maximum (as long as the acceleration increases/decreases monotonically to/from the maximum). This may or may not be what you want.

Re: Why roller coaster loops aren’t circular anymore

#56

Post by bergenty »

joshu wrote: post #36
mkl wrote: post #35

Thus is similar to corners in roads not working well when they're circular arcs. Going from straight to circular arc means your steering wheel needs to jump instantly from one fixed position to another. Using something like a linear change in curvature (i.e. a clothoid curve) is much smoother. This kind of thinking applies to other areas too: https://en.wikipedia.org/wiki/Euler_spiral

for exactly the same reasons the corners of apple products aren't just an arc. They change the tangent smoothly over time. Curiously Dubins paths do have instantaneous steering changes. https://en.wikipedia.org/wiki/Dubins_path

Changing tangents smoothly over time is an arc

Re: Why roller coaster loops aren’t circular anymore

#57

Post by ssl232 »

userbinator wrote: post #37
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…

This effect can be prevented by gradually letting off the brake before reapplying it fully upon stopping, but few drivers and rapid transit systems are aware. This is surprising to read. Everyone whose car I've ridden in knows to do that, and it's only in extremely urgent and unexpected stops where it's neglected. Also, when fully stopped, only minimal pressure should be necessary to keep the car still.

> Also, when fully stopped, only minimal pressure should be necessary to keep the car still.

Why? To keep the brake fluid lines from bursting or something?

Re: Why roller coaster loops aren’t circular anymore

#58

Post by lqet »

userbinator wrote: post #37
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…

This effect can be prevented by gradually letting off the brake before reapplying it fully upon stopping, but few drivers and rapid transit systems are aware. This is surprising to read. Everyone whose car I've ridden in knows to do that, and it's only in extremely urgent and unexpected stops where it's neglected. Also, when fully stopped, only minimal pressure should be necessary to keep the car still.

> Everyone whose car I've ridden in knows to do that

I also do that, and don't know anyone who doesn't. I vaguely remember that I learned it in driving school, most likely because my driving instructor didn't want to be jerked around on the passenger seat for an hour every week.

Train/tram drivers here also usually do that in stations, except when they try to make up for delays, or when they have wrongly estimated the breaking distance.

Re: Why roller coaster loops aren’t circular anymore

#59

Post by quchen »

bergenty wrote: post #56
joshu wrote: post #36

Earlier quoted context omitted.

for exactly the same reasons the corners of apple products aren't just an arc. They change the tangent smoothly over time. Curiously Dubins paths do have instantaneous steering changes. https://en.wikipedia.org/wiki/Dubins_path

Changing tangents smoothly over time is an arc

Smooth often means that higher derivatives are continuous as well. A straight line changing into an arc has continuous first derivative, but the second is discontinuous.

Re: Why roller coaster loops aren’t circular anymore

#60

Post by rhn_mk1 »

ben_w wrote: post #34
keithnz wrote: post #20

Earlier quoted context omitted.

I have a t-shirt which has "don't be a" and the equation for the third derivative

Reminds me of someone I knew at university whose T-shirt was the definite integral from 10 to 13 of 2x dx followed by a question mark.

...9?
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