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Wednesday, May 7, 2008

Distance, speed, acceleration, and time

"Parsley, sage, rosemary, and thyme" — refrain from Scarborough Fair
TheBigHenry quoting BigAl
Kinematics in spacetime analyzes distance as a function of time. The derivative (i.e., rate-of-change) of distance with respect to time is speed, which itself is also a function of time. Furthermore, the derivative of speed with respect to time is acceleration, which, in general, is a function of time as well.

Most people who are familiar with the quoted ballad refrain are also conversant with the physical concepts of the title. But, what is the next derivative in this physical series? Well, the first derivative of acceleration, or second derivative of speed, or third derivative of distance (with respect to time) is called jerk. Just as acceleration is the "speed" of speed, jerk is the "speed" of acceleration or, alternatively, the "acceleration" of speed. Is there a point to all this jerking around?

Well, if you multiply a jerk by mass you get a yank. In particular, if the acceleration happens to be grave, the force of the mass becomes the weight of the mass, and the yank is converted to a wank. Moreover, the latter concept has important applications in Britain, where, by coincidence, Scarborough is located!

All of which presages the following hidden message, if you're into that sort of thing:
A Yank jerk and a Brit wank are "birds of a feather" (so to speak), as it were.

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