Friendly gesture shocking

Answer: In a classic 1953 story, a professor was driving slowly when two friends pulled up alongside, matching his speed, says Jearl Walker in "The Flying Circus of Physics." The friend in the passenger side reached out to hand a package of gum to the professor. But when the two hands got within an inch or two of touching, a terrific discharge occurred between them that was momentarily disabling. "Luckily, the professor did not veer into the second car before he could regain his senses and the control of his car."

The spark occurred because the motion of the cars electrically charged the professor and the friend by different amounts, possibly even with one charge being positive and the other negative. "When the two hands were close enough, electrons from one jumped across the air gap to the other, reducing the charge difference" — and ZAP!

Question: Imagine all the world's people standing one in front of another in lines a mile long, and with lines shoulder to shoulder stretching a mile wide. The people left over would have to stand on the shoulders of those below, forming a gigantic human "block." Puzzle: How high would the block need to be to squeeze in all of the world's 6+ billion population?

Answer: 1 mile B. 10 miles C. 100 miles D. 1,000 miles

A: Surprisingly, A. Figure that there are 150 billion cubic feet in a cubic mile (5,280 x 5,280 x 5,280), which when divided by 6.4 billion = 23 cubic feet per person — "enough for all of us to squeeze in," with ample breathing room left over, say Edward Burger and Michael Starbird in "Coincidences, Chaos, and All That Math Jazz."

Question: Wow, a Roman numerals equation, but it's not correct: No way that 11 + 1 = 10. Without using a pencil, how might you fix it? You'll flip at how easy this is.

XI + I = X

Answer: At least three fixes here: (1) Rotate the page through 180 degrees (2) View the page right side up but reflected in a mirror (3) If the page is at least partly translucent, turn it over and view the equation through the rear side. (From "A Beginner's Guide to Immortality" by Clifford Pickover)

Question: Why the powerful appeal of "monkey see, monkey do" for us humans?

Answer: Credit "mirror neurons" that fire every time you make a move, like opening a can of soda, says Ingfei Chen in "Discover."