Spinning: Dentist's drill tops a cycle

Q. As things get revved up, which spins faster, your computer's hard drive, your car's engine, or your dentist's drill? ­M. Goround

 A. Today's hard drives go at 10,000 revolutions per minute (RPM) or more, faster than your car's 5,000 RPM internal-combustion engine but slower than your motorcycle's 15,000, says University of Michigan professor of automotive engineering Thomas D. Gillespie.

Routers will outturn these at 20,000, plenty of home-drill-rotary-type tools spin up to 25,000, all topped by turbo-chargers driven by the engine's exhaust gases and running hot at 100,000 for turbine and compressor, says Gillespie. Racing car and jet turbine engines can hit in the 100,000s; and at Massachusetts Institute of Technology one tiny experimental turbine with a pea-sized wheel was said to RPM at around a million.

Don't let your dentist get hold of one of those: Her high-speed drill is bad enough at 300,000 RPM.


Q. Old entomologist's joke: What's the last thing that runs through a bug's mind when it hits a car's windshield? ­D. Straits

 A. Its rear end, as the bug flattens like an accordion. Hah!

Fascinatingly, these windshield plasterings can form patterns so individual and eccentric they leave a telltale signature, depending on speed, type of vehicle and insect, says the University of Florida's Mark Hostetler, self-described "splatologist" and author of That Gunk on Your Car.

He has driven thousands of miles with a netted contraption on his automobile to correlate splat-patterns– e.g., a flying ant's splat is "usually a watery, small white smear 8-15 mm in length." Make that a SUV or Greyhound bus, and the signature might be quite different.

Taking splatology to a cosmic level, NASA in Horse Flies and Meteors says Earth, like a fast car, races around the Sun sweeping up small asteroids and bits of cosmic dust.

"They hit Earth's atmosphere splat!– and disintegrate as fiery streaks of light called meteors." But as with bugs, how they hit matters, whether frontally, side or rear. And as with bugs, side hits can be most dramatic, leaving long colorful sky streaks ("Earthgrazers").

And that's no joke!

Q. From the Mendelian genetic standpoint, what is it that makes sex so super? Or answer this: If you cross purebred tall pea plants with purebred short ones, will you get a) mostly tall offspring plants? b) mostly shorts? c) mostly plants of intermediate (blended) heights? ­J. Seabrook

A. When 19th-century monk Gregor Mendel tried this, he got all talls in the first generation, then when he fertilized these hybrids with their own pollen, short progeny reappeared, in a ratio of 3 talls for every 1 short.

So the answer is "a." Instead of the plants winding up with blended or averaged offspring of intermediate height, the tall genes dominated, then the recessive short ones reappeared the following generation.

And herein lies the answer to what makes sexual reproduction so super: It fosters a constant mixing of traits that have been selected in the past and helped keep the species vibrant and competitive. As genes work, many of these traits are not averaged out and thus lost, but are retained for "assembling" into promising new combos, and often in far more complex ways than with Mendel's peas.

If a mere averaging out of genes were the full story, people would soon wind up all looking and being pretty much the same, like clones, says Texas A&M University evolutionary geneticist Thomas J. DeWitt. The problem is that when an environmental assault occurs, we would all have the same vulnerabilities and none of us would be able to survive the change. End of human story!

Q. If it weren't for "flicker fusion," there never would have been Independence Day, Godzilla, Gone With the Wind, or any other famous or infamous flick. What's flicker fusion, anyway? ­F. F. Coppola

A. Turn a bright light off in a dark room and your eye-brain system won't register the turn off for a split second as the image fades in memory. If you could turn the light on and off extremely rapidly–say 48 times a second– the brief bright bursts would fuse into one seeming continuous light.

That's the flicker rate of many motion pictures (24 frames/second, each frame flashed twice), leading to apparent continuous action even though if you could slow things down enough and take a look, the screen would in fact be totally blank much of the time.

Send Strange questions to brothers Bill and Rich at StrangeTrue@Compuserve.com.