STRANGE BUT TRUE- Dirty dogs: Actually, your mouth has more bacteria

DRAWING BY DEBORAH DERR McCLINTOCK

Q. Is it true there are more germs in the human mouth than around a dog's anus? –R. T. Tin

A. The usual comparison is between the human mouth and dog's mouth, not the dog's other end, says Dr. Joseph Zambon of the University of Buffalo School of Dental Medicine.  

Some 200-300 different bacterial species may hang out in the human oral cavity, plus viruses and other microorganisms. Certainly, people with diseased gums have more bacteria and more types of bacteria than dogs with healthy mouths.

"But you can make the other, more colorful comparison as well. There are higher concentrations of bacteria in human dental plaque than in a dog's feces." So you might extend this to include the dog's alimentary exit point as well.

Q. Few people survive falls from very great heights. When they do, what may be the physics at work? –I. Carus

A. The victims reach a "terminal speed," where air drag offsets acceleration and falling speed maxes out, at maybe 100-200 miles per hour, says Jearl Walker in The Flying Circus of Physics. The other critical factor is how they land. A "hard" collision may last for only 0.001 to 0.01 second, with the force certain to be lethal. But for a "softer" collision (taking longer to stop), survival becomes possible:

1. February 1955: A paratrooper fell 370 meters (1,200 feet) from a C-119 airplane without managing to deploy his parachute. He landed on his back in soft snow, creating a crater a meter deep. Air-evacuated to a hospital, he had only minor bone fractures and a few bruises.

2. World War II: I.M. Chissov, a lieutenant in the Soviet Air Force, bailed out when attacked by a dozen Messerschmitts. To avoid being a "sitting duck," he delayed deployment of his parachute. Unfortunately, he lost consciousness during the seven-kilometer fall (over four miles). Fortunately, he hit a snowy ravine, and although injured, was back in uniform within four months.

3. More bizarre was Henri LaMothe's 1970s stunt of diving from 12 meters (39 feet) and belly-flopping into a pool of water barely 30 centimeters deep (about 12 inches), hitting with a force about 70 times his body weight. Apparently this amount of cushioning water was enough. ("Don't try this," warns Walker. "One foolish guy who did ended up paralyzed from the neck down.")

Q. What's a major league baseball pitcher's secret to throwing a sharp-breaking curve ball? –C. Young

A. Oddly, this classic weapon may have more to do with the batter himself than is commonly suspected. A spinning baseball actually moves in a smoothly curving trajectory but seems to change directions suddenly.

Psychologist Arthur Shapiro of Bucknell University offers this: Viewers who look directly at a pitched baseball perceive it correctly as moving downwards under the influence of gravity, while those viewing it out of the corner of their eye perceive it to be moving at an angle. 

Perhaps when we use our peripheral vision system, the brain uses internal motion cues to interpret overall direction, so the ball appears to move to the side. In other words, the pitch starts off in the center of a batter's foveal vision but then overlaps the peripheral system as the ball draws closer and closer, forcing the batter to shift his visual attention. 

"This transition may be why such balls appear to change direction suddenly," Shapiro adds. Interestingly, the U.S. Vision Sciences Society has voted the curve ball as "Visual Illusion of the Year" for 2009.

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Send Strange questions to brothers Bill and Rich at [email protected].

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