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Re: [Phys-l] Linear Air Drag

At first I thought, Gee, an energy principal use that's much simpler than force, but no, if anything, it's more difficult, but as Carl wrote quite heuristic.

His method reminds me of Siegel's pendulum damping analysis. AJP. 76 Oct. 2008.

Period-speed analysis of a pendulum

We analyze a simple pendulum by measuring the period and the maximum speed of the bob. Both
quantities are measured to high precision using a laser diode and an infrared photodetector located
at the bottom of the pendulum. Expressing the period in terms of the maximum speed enables
students to examine the large angle dependence of the period, and provides a method to calibrate the
speed and do a detailed analysis of the effect of air friction on a sphere. We find that the force due
to air friction is well described by a linear and quadratic term in the speed. We investigate the
dependence of each term on the sphere’s diameter for Reynolds numbers from 250 to 104. © 2008
American Association of Physics Teachers.
DOI: 10.1119/1.2937897


bc added a Coulomb term for his pendula.

p.s. Taylor's book?

On 2009, Nov 03, , at 07:22, Carl Mungan wrote:

If you'll excuse the shameless self-promotion, a nice case one can do
analytically is purely vertical up and down motion in the presence of
drag (quadratic or linear). An interesting approach is to do so using
energy methods rather than integration of Newton's second law:

http://usna.edu/Users/physics/mungan/Publications/EJP3.pdf

I've taught such ideas in the intermediate mechanics course and used
Taylor's book (which I highly recommend). -Carl
--
Carl E Mungan, Assoc Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/
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