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Beyond velocity and acceleration: jerk, snap and higher derivatives (2016)

(iopscience.iop.org)
181 points EndXA | 1 comments | 19 Jun 24 10:16 UTC | HN request time: 0s | source
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londons_explore ◴[19 Jun 24 11:39 UTC] No.40727286[source]▶
I wish designers of vehicles - particularly cars, trains and busses, would work to minimize jerk, snap and crackle.

Turns out if you minimize those, you get a far more comfortable ride. It matters far more than acceleration.

Finite element models of the whole system (tyres and suspension components and flexing elements of the vehicle body and road/track) can quickly allow analysis of the jerk, snap and crackle, and allow tuning of damping and drive system control loops to make a far more comfortable ride.

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amelius ◴[19 Jun 24 11:42 UTC] No.40727304[source]▶
Do you have proof for that, or is this like audiophiles asking for gold connectors because "they make the sound better"?
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setopt ◴[19 Jun 24 11:53 UTC] No.40727380[source]▶
Anecdotal evidence:

Ever experienced that a bus is braking (near-constant deacceleration), and people seem fine; but then the bus comes to a halt and thus stops deaccelerating, and people suddenly fall on the floor?

I think at least the derivative or acceleration is important for how well people can compensate. Not sure about higher derivatives though.

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1. tomek_ycomb ◴[19 Jun 24 18:52 UTC] No.40731289[source]▶
I think bus is braking with a constant breaking force.

But, the bus has a non-constant kinetic energy (going up with the velocity*velocity, down as velocity goes down.)

So, you're actually producing a non-linear acceleration. This is jerk, but you can also think of it as just a non-linear acceleration and people are reacting to the fact it's not at all near constant deacceleration, and this is most noticable as velocity hits zero.

So, yes, it's jerk, but no, I think it can be intuitively better understood with pure acceleration terms and no jerk needed