Monday, November 23, 2009

jerk and jounce

this may get a little technical. i have to share some new words that i always wondered about: what do you call a change in acceleration over time?

what i always mistakenly called 'impulse' is actually called jerk, jolt, surge, or lurch. and it is the instantaneous change in acceleration of an object with respect to time.

in physics one learns about position, velocity, and acceleration, and how they are all mathematically related (i.e. velocity is the time derivative of position; acceleration is the time derivative of velocity). but if you are like me you wondered what comes next.

i had heard the word impulse used for the time derivative of acceleration once and i never questioned it, but as i now know this is most commonly referred to as jerk, and it has units of meters per second per second per second (m/s³)

if we take this a step further we get jounce (aka snap) in meters per second to the fourth power.

time derivatives past jounce fade quickly in naming convention, but according to wikipedia:
Currently, there are no well-accepted designations for the derivatives of jounce. The fifth and sixth derivatives of position as a function of time are "sometimes somewhat facetiously" referred to (in association with "Snap") as "Crackle" and "Pop", from the cereal characters; however, these terms have not gained widespread acceptance.
an essay from the university of california, riverside suggests some names for multiplying each of these by mass:
Now class, repeat after me. . .
Momentum equals mass times velocity!
Force equals mass times acceleration!
Yank equals mass times jerk!
Tug equals mass times snap!
Snatch equals mass times crackle!
Shake equals mass times pop!!

[jerk and jounce via wikipedia]

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