[Dixielandjazz] Slide trombones
arnieday at optonline.net
Mon Mar 21 15:13:50 PST 2005
I'm sorry to have to correct you, Paul. If you slice a cone parallel to
it's axis, one does not get a parabola, but a starnge piece of material
whose mathematical description depends upon whether the cone was solid
or hollow. On the other hand, if you remove the skirt from the girl at
the bar, fill it with straw, set it on the floor on its hem, take a
sharp box-cutter and slice it horizontally, you will find that, by the
time you have done all this, the trombone player will have disappeared
with the girl.
Edgerton, Paul A wrote:
>Time for another DJML science lesson: today's word is "parabola."
>A parabola is a conic section. That is, one can take a cone standing on its
>circular base -- a trombone will do nicely -- and slice it parallel to the
>axis of the cone. The resulting curve is called a parabola. Anybody who
>has seen the Gateway Arch in St. Louis or watched a perfectly thrown "Hail
>Mary" pass has seen what I'm describing. (Kids! If you try this experiment
>at home, use a sharp band saw -- but ask permission first!)
>The mathematically significant feature of a parabola is that it has a focal
>point. In the case of a trombonist, the focal point is typically seated at
>the bar in a short skirt.
>When a parabola is rotated through space about its axis, it forms a
>paraboloid. One common paraboloid is a satellite dish antenna. Another is
>the reflective surface of an old-style automotive headlamp. If a trombonist
>is rotated about his axis, he gets dizzy. The same effect is generated when
>he sits at the bar next to the skirt.
>The purpose of a horn is to couple an acoustic radiator with the focal
>point, so it isn't correct to say a brass instrument's bore is parabolic.
>Now that you have now been properly educated, you can avoid making
>embarrassing mistakes like this in conversation with the skirts at the bar.
>All brass instruments have bores that are conical, and most contain
>cylindrical sections to accommodate things like tuning slides. The trumpet
>and trombone, in particular, have a bore that is predominantly cylindrical
>with the conical sections being mainly in the lead pipe and bell.
>Wait a minute, I have just received new information that the primary
>definition of the word "parabolic" is "Of or similar to a parable."
>Ahem, please forget I ever mentioned the skirt at the bar.
>-- Paul Edgerton
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>Dixielandjazz at ml.islandnet.com
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