-I’ve heard dimpled golf balls fly further than a smooth sphere when hit. Same phenomenon?
What happens is that at high enough speeds, air molecules are trapped (sort of cling) to the surface (whatever the surface is on) and then other air slides against those air molecules, drastically reducing friction.
I don’t know about golf balls, as I think neither the speed, nor the bumpiness is large enough, but I am willing to be proven wrong.
Mostly, I had heard of it used in jets (fighter jets mostly, and hypersonic I think too). If you ever feel a fighter jet wing, I think it is rough… and that would be why…
Nico
I will now prove myself wrong:
http://entertainment.howstuffworks.com/question37.htm
The airflow thing is exactly why golf balls are dimpled.
OK Doug, you are a pain in the dimpled arse. Now I have to explain about resonators to yous guys. It is a lot of trouble and some will make fun of me because I’m talking physics stuff but you really need to know about the Q of competing resonator modes, having been in engineering, you probably know it anyhow, but here it is at least for the others who are interested
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Story: “The Q of Competing Resonators Modes” or “Our Temperamental Perpetual Motion Machines”
The oscillator world is made up of resonators. Examples are: pendulum clocks; in fact all clocks; a child’s swing; electronic oscillators used in radios and most other electronic equipment; a bouncing ball; a laser; a musical instrument; and a molecule. In fact, anything that vibrates. A resonator is a gadget that supports vibration of something, like a flute. Resonators can vibrate at only one frequency or many frequencies at the same time (often harmonically related, like a GOOD flute). All resonators have vibration from energy of motion (kinetic energy) to an equal amount of stored energy (potential energy) each cycle. A bouncing ball has its kinetic energy as it hits the ground and potential energy at the top of its bounce. A pendulum and a swing have kinetic energy at the bottom of the swing and potential energy at the top of the swing. In an ammonia molecule, there is a nitrogen atom in the middle of a triangle of three hydrogen molecule, NH3. The vibration of the N, as a drum head, in the middle of the three H atoms, makes the most accurate clock ever made, it looses one second in every 3,215,020 years. I have two ammonia clocks, in 3,215,020 years I’ll check them and see which one gained a second. An electronic resonator is a coil hooked to a capacitor. The stored electrical energy goes from the kinetic energy in a coil to the potential energy in the capacitor. In a flute the molecules squeeze up in the middle of the tube as potential energy and move out in both directions as kinetic energy and the potential energy is stored in the stretched out molecules, as an accordion like spring.
Besides the frequency of a resonator (cycles per second, like A is 440), the second most important thing to describe a resonator is its Q, or quality factor. A high Q musical instrument loses little energy each cycle. It rings for a long time after you quit plucking, blowing, bowing, striking. A bell has a high Q. One flute said to the other, “How’s your Q today?” “It’s down, someone spit in me, thank you.” Quantitatively, the Q is the energy stored per cycle divided by the energy lost per cycle. This turns out to also be the ring time multiplied by the frequency. If a violin diminishes the A note in one-half second after stopped bowing, the Q is 1/2 x 440 = 220 = Q. One violin said to the other, “What’s your Q today?”. “It down to 197, some SOB stuck some chewing gum on my bridge”. In order for a resonator or clock to ring, you have to add energy each cycle. Like a kid in a swing moves their arse up and down each cycle to add the potential energy at the right time; like the spring-and-ratchet on a clock adds energy to the pendulum each swing; like an amplifier between the coil and capacitor of an electronic oscillator adds energy each cycle; like the blowing over the hole in the flute adds energy to the “springing” air in the flute. The amount you have to add has to be equal to the loss in the flute plus the loss of radiation (music). This is called feeding the oscillator. I have gone to all this trouble to say the following: The energy in each mode (harmonic) of an oscillator, very easily jumps from one mode to the other, depending on the relative (and slight) change in Q of the two modes. Also, roughness and texture of the wall changes the Q in very complicated ways. You take a smooth gulf ball and I’ll take a dimpled one and we will see which one has the most slice and goes the farthest. Get rich by inventing a gulf ball with a surface that has less loss from the wind.
So the roughness of the walls of the pipe will change the mode in a very delegate way. Duplicateability is going to be a problem, maybe.
Really good Q in those descriptions…I’m saving that description for future reference.
For modes to compete, they need also to have some degree of coupling. The modes for a change between notes within a given octave are sufficiently seperated in frequency such that the coupling is very weak. (as an aside…within a given mode the Q is related to how much you can “pull” a note) So the flute isnt going to jump to A when you are holding G.
Harmonics (for instance octave jumps) are another matter. In this case the modes are coupled through the non-linearity of the driving source and are all driven at the same time. In a high-Q flute, with glassy smooth walls and very good tuning between octaves (like the keyless Noy) this can keep your attention! Best analogy I can think of is driving an oversteering car (like an autocross Corvair or Porsche) If you think about an octave change (or a turn)…it will!
The “steering wheel” on the flute is the harmonic content of the driving force from the embrouchure. You can play with this and watch the modes on a spectrum-type tuner. (like the one on T.McGee’s site which if a free download)
Got to run..later..
Jack