STRANGE BUT TRUE- Bad vibes: Bridges, breasts, brews all bounce
Q. What do the tragic Tacoma Narrows Bridge collapse of 1940, your coffee cup sloshover, and the need for the modern sports bra all have in common? –P. Anderson
A. All involve resonant frequencies run amok, says UVA's own Louis Bloomfield in How Everything Works. Rhythmic pushes can cause objects to vibrate strongly, such as when wind set the Tacoma Narrows Bridge in Seattle to vibrating and twisting back and forth so that one lane rose as the other fell. "During the storm, so much energy was added to the natural resonance that the bridge ripped itself apart."
The far less serious coffee spillage occurs when the liquid jostles back and forth in synchrony with the frequency of your walking, says Bloomfield. Walking or running can also set various body parts to vibrating resonantly: Some women may find running uncomfortable when their breasts oscillate vigorously in tandem with the frequency of their strides. Sports bras have made running more painfree by stiffening the restoring forces on each breast and thus breaking up the frequency coincidence.
Q. What if during a two-week period of your writing a math textbook chapter on coincidence, five famous people all died? Wouldn't you begin to wonder what was going on? –L. Carroll
A. That's what happened to Edward Burger and Michael Starbird while writing The Heart of Mathematics. Suddenly dead were TV celebrity Brian "Uncle Bill" Keith, deep-sea diver Jacques Cousteau, actors Robert Mitchum and Jimmy Stewart, and news commentator Charles "On the Road" Kuralt.
"This seemed to us a very strange public coincidence," Starbird says.
So the authors decided to analyze it. At least 50 million people died that year, or about 1 million per week. Now the question became: Among the roughly two million who die in any two-week period, how likely is it that five of them are famous? Conservative guesses of famous people in different categories produced 300 singers, 600 actors, 600 sports figures, 1,200 leaders, etc.
"Let's say there are 4,000 in the world, nearly all of them famous for less than 40 years. So we estimated at least 100 must die each year, or about two per week, putting our five noted deaths pretty much on target. A world almanac listing people who died that year had 105 names, again, reasonably accurate," he adds.
Of course, countless other coincidences could have occurred during that two-week period, further diminishing the five-death significance. "Looked at in this way, many coincidences lose some of their luster," Starbird concludes.
Q. Does being a "rightie" or a "lefty" matter for a racehorse? –S. Biscuit
A. Horse trainers and riders often say their animal performs better when running, turning, or jumping in a particular direction, says New Scientist magazine. To test this, Jack Murphy of the University of Limerick in Ireland checked 40 unschooled sport horses to see which leg they stepped forth with, which direction they chose to detour around an obstacle or roll over in a bed of hay.
He found that most female horses seemed to prefer their right side, males their left. Around 10 percent used both sides. (Dogs and chimps show sex-biased "handedness" as well.) "As a perfectly balanced horse is most desirable, trainers could use such information to help develop their horse's weak side," says Murphy.
It could also help trainers and punters decide where racehorses run best, as the direction of each race and the bends involved will suit some thoroughbreds better than others. Concludes New Scientist, putting your money on the ambidextrous horse may be key to beating the bookies' odds.
Q. Could you pick up a dollar bill with a magnet? –B. Gates
A. A large electromagnet would pick up a U.S. dollar– though not all currencies– because it is printed with magnetic ink, says James Livingston, author of Driving Force: The Natural Magic of Magnets. You can prove this by hanging the bill freely from a corner and watching it flutter in midair as you pass a magnet nearby.
For a more dramatic demo, pour 200 ml of water into a blender, crumple up a dollar bill and toss it in, suggest David Brooks of the University of Nebraska-Lincoln and Robert Becker of Kirkwood High School in Kirkwood, Missouri. Blend for 3-4 minutes while holding a strong magnet to the outside of the glass. When you remove the magnet, see the black ink spot gathered there!
"A white plastic spoon behind the spot displays the dark color," says Brooks.
For you teachers, your students will be amazed how much iron is in a single bill, says Becker. But a word of caution: You're destroying legal tender, so remind the class, it's all in the name of science.
Send Strange questions to brothers Bill and Rich at firstname.lastname@example.org.