7 ms·

Jerk is also a limit in how fast a subway can move between stations. There is a clear limit to how much jerk average standing passengers can survive before the

Jerk is also a limit in how fast a subway can move between stations. There is a clear limit to how much jerk average standing passengers can survive before they fall down.

palakchokshi 13y ago
Jerk is also the guy talking loudly on his cellphone while a subway moves between stations. There is a clear limit to how much jerk average standing(or sitting) passengers can survive before they fall down on the guy and knock his teeth out. :)
- jessaustin 13y ago
  I always wondered if there were a sociological commentary in the fact that yank is defined as jerk * mass.
  - palakchokshi 13y ago
    aaaah so the bigger the jerk the harder you have to yank him to bring him down?
    - jessaustin 13y ago
      Actually no I thought the term might have been coined by British physicists after spending too much time around us Americans...
hueving 13y ago
I don't think this is the limiting factor in most subway systems though. I've never been on one that accelerated during the entire first half of the segment and decelerated during the second half at the same rate, which would be the case if they were being limited by jerk.
- simcop2387 13y ago
  Might not be in most but it certainly is for some. The subway in the Atlanta Hartsfield Jackson airport accelerates and decelerates that way. It makes it feel like you're probably going way faster than you are. I've seen just a few people almost fall over if they aren't holding on properly.
- pessimizer 13y ago
  >I've never been on one that accelerated during the entire first half of the segment and decelerated during the second half at the same rate, which would be the case if they were being limited by jerk. No, that would be the case if the only limit was jerk. When stations are close to each other, it feels like this is exactly what happens.
- shasta 13y ago
  The acceleration curve you describe would have infinite jerk at the start, stop and halfway points. A |jerk| minimizing curve for a fixed travel time would gradually (linearly) increase to maximum acceleration during the first 1/4 of the trip, gradually decrease back to no acceleration over the next 1/4, gradually increase to full deceleration over the next 1/4, and finally gradually decrease to no deceleration over the last 1/4.
- ams6110 13y ago
  DC-powered rail systems such as the Chicago "L" can be jerky because the motor controllers are stepped not continuous. It's basically late 19th/early 20th century technology. The AC-powered systems in their newer rolling stock offer smoother operation.
_Robbie 13y ago
I think the stops would have to be very close together for this to be a factor. If a train trip is jerk limited, then the train would not reach maximum acceleration between stops. It is more likely that a train trip is acceleration limited where the train does not reach full velocity between the stops.

Jerk is also a limit in how fast a subway can move between stations. There is a clear limit to how much jerk average standing passengers can survive before they fall down.

palakchokshi 13y ago

Jerk is also the guy talking loudly on his cellphone while a subway moves between stations. There is a clear limit to how much jerk average standing(or sitting) passengers can survive before they fall down on the guy and knock his teeth out. :)

jessaustin 13y ago
I always wondered if there were a sociological commentary in the fact that yank is defined as jerk * mass.
- palakchokshi 13y ago
  aaaah so the bigger the jerk the harder you have to yank him to bring him down?
  - jessaustin 13y ago
    Actually no I thought the term might have been coined by British physicists after spending too much time around us Americans...

hueving 13y ago

I don't think this is the limiting factor in most subway systems though. I've never been on one that accelerated during the entire first half of the segment and decelerated during the second half at the same rate, which would be the case if they were being limited by jerk.

simcop2387 13y ago
Might not be in most but it certainly is for some. The subway in the Atlanta Hartsfield Jackson airport accelerates and decelerates that way. It makes it feel like you're probably going way faster than you are. I've seen just a few people almost fall over if they aren't holding on properly.
pessimizer 13y ago
>I've never been on one that accelerated during the entire first half of the segment and decelerated during the second half at the same rate, which would be the case if they were being limited by jerk. No, that would be the case if the only limit was jerk. When stations are close to each other, it feels like this is exactly what happens.
shasta 13y ago
The acceleration curve you describe would have infinite jerk at the start, stop and halfway points. A |jerk| minimizing curve for a fixed travel time would gradually (linearly) increase to maximum acceleration during the first 1/4 of the trip, gradually decrease back to no acceleration over the next 1/4, gradually increase to full deceleration over the next 1/4, and finally gradually decrease to no deceleration over the last 1/4.
ams6110 13y ago
DC-powered rail systems such as the Chicago "L" can be jerky because the motor controllers are stepped not continuous. It's basically late 19th/early 20th century technology. The AC-powered systems in their newer rolling stock offer smoother operation.

_Robbie 13y ago

I think the stops would have to be very close together for this to be a factor. If a train trip is jerk limited, then the train would not reach maximum acceleration between stops. It is more likely that a train trip is acceleration limited where the train does not reach full velocity between the stops.