Surviving a fall, thanks to snow
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Q. Few people survive falls from very great heights. When they do, what may be the physics at work?
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. For example, in Feb. 1955, A paratrooper fell 370 metres from a C-119 airplane without managing to deploy his parachute. He landed on his back in soft snow, creating a crater a metre deep. Air evacuated to a hospital, he had only minor bone fractures and a few bruises.
During the Second World War, 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 kilometre fall. Fortunately, he hit a snowy ravine, and although injured, was back in uniform within four months.
Q. What’s a major league baseball pitcher’s secret to throwing a sharp-breaking curve ball?
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 centre 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.
Q. In a tug-of-war pitting two teams of horses, eight per team, against atmospheric pressure, which wins?
A. It was 1654 and German physicist Otto von Guericke had audience before Emperor Ferdinand III to demonstrate the “Magdeburg hemispheres.”
About a foot in diametre, they were fitted together to form a sphere, then the air was pumped out to create a vacuum inside. Now powerful suction pulled the halves together, or more accurately, they were pushed together by air pressure from the outside.
Think of atmospheric pressure as the weight of a column of air an inch square going up several miles.
This column weighs about 15 pounds for the square inch, i.e., that’s atmospheric pressure. Since von Guericke’s sphere was about 15 inches in diameter, its “effective” surface area per hemisphere was about 180 square inches, meaning the weight of the invisible atmosphere pushing on each hemisphere was nearly 3,000 pounds!
Too much for the 16 tugging horses. The air won.
Send STRANGE questions to brothers Bill and Rich at Strangetrue@cs.com
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