2014-06-28

Jerk

I neglected to mention regarding the acceleration videos the concept of "jerk".   Basically, it refers to the rate of change of acceleration.   That is to say, we often just default to concepts of constant acceleration for ease, but in reality acceleration itself usually changes over time.

So, for instance, if you're riding in a car and the driver hits the gas pedal, no matter how quickly he does so a number of things prevent the vehicle from instantly assuming its maximum acceleration.   The travel of the pedal, the response of the computer in regards to fuel injection (or simply the opening of the doodads related to the carb), the time it takes the engine to rev up, that power going to the transmission which has its own things to do, et cetera.   Long story short, the tires simply don't instantly start spinning at maximum (and even if they did you'd probably just get squealing tires anyway unless and until some friction could be restored to the mix).

The experience in the seat, then, is going to involve an increase of acceleration over time.  

The same thing happens in non-automotive contexts, as well.   Shuttle solid rocket boosters were throttle-able, but even so they didn't achieve the intended acceleration at particular throttle settings immediately.  I see no real reason to assume the same wouldn't be true of science fiction vessels . . . though if a sci-fi vehicle can achieve 1000g acceleration (for example), one would presume it wouldn't take very long at all to get to, say, 20g.

The videos made thus far do have jerk only inasmuch as SketchUp forces the matter, but generally speaking are not intended to have any jerk (or for all jerk to happen instantly on start, if you prefer to think of it that way).   The goal is to show the result of constant acceleration assuming that maximum acceleration can be achieved instantaneously from a standing start.

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