Net loss: Cannonballs need good aim

Q. How does a "human cannonball" survive being shot out of a circus cannon without getting blown to bits? ­P.T. Barnum

 A. That part is easy, since the "explosion" is all theatrics, mere pop and puff, with the propulsion provided by a catapulting spring or compressed air, say David Halliday et al. in Fundamentals of Physics. But the dangers are real, considering the performer usually blacks out momentarily from muzzle acceleration and must awaken before landing in the net or risk a broken neck! Second great danger is summed up by "Flying isn't the hard part, managing to hit the net is."

The stunt was made famous by the Zacchini circus family in the 1920s, then culminating a few decades later when Emanuel Zacchini was shot at 60 mph over three 60-foot-high Ferris wheels, clearing them by 15-20 feet and landing in a net some 225 feet from launchpoint. That one worked out OK, but somewhere down the Zacchini gene line, two daredevils cannon-balling from opposite ends of a circus accidentally collided in midair, breaking the back of one of them.

Q. When Earth ends, what happens to the human race? ­Worried in Charlottesville

 A. Ultimately, our species' days on Earth are numbered, says physicist Lawrence Krauss in Beyond Star Trek. Whether because of war, pollution, global warming, an asteroid or comet zeroing in, a nearby exploding star, old age weakening the planet's magnetic field shield, the rotational braking effect of the moon, etc., if we humans are around long enough, we will have to leave. Maybe fast!

Forget round-trip travel. The idea will be to just head out and survive. What we'll need, says Krauss, is an environment capable of generating artificial gravity and filtering or deflecting harmful cosmic rays. With a lucky several million years to get ready, maybe even we notoriously short-sighted humans will rise to the task.

We may require mammoth voyaging systems designed to hold thousands of generations as we search for a home. "I trust that if our spaceships make it to a safe harbor... we will present ourselves more generously than the visitors in the movie Independence Day."

Even if we can't make a getaway, all is not hopeless. Maybe in the final catastrophe, such as a comet smashing Earth, torrents of planetary matter will be ejected into space, containing "organic materials that provide the blueprint of our existence." Just as long ago atoms for our bodies were cooked up in fiery distant supernovae, which may have sacrificed existing life forms, we may return the favor as "we bequeath our own organic material to the universe."

Q. It's been said your best bet in fleeing a pursuing crocodile on land is to outwit it by running away in zig-zag fashion. True, or a crock? ­S. Irwin

A. That's an old myth, and would only up your odds of becoming lunch, says British zoologist Dr. Adam Britton, author of crocodilian.com. The fastest way of putting distance between yourself and a crocodile is a straight line run. If you're fit, you should easily win this race.

Some wild speed figures, such as 40 mph, are in TV documentaries, but 8-10 mph is more like it for a short run for most crocodiles, possibly 12-20 mph for a brief burst of several feet as they launch themselves out of the water. Fact is, crocs are not pursuers but ambushers. To get away, you have to see one coming. "Never underestimate the attacking speed of a crocodile from a standing start."

Q. Puzzle for all you bright readers: In a closed room are three light bulbs, and in the hall outside are three switches to these bulbs. Your task is to find which switch controls which bulb. You can enter the closed room once. There are no other restrictions. Each switch operates in the usual way... up = on, down = off. ­M. VosSavant

A. Solution: Switch A you never turn on, switch B you turn on for five minutes then off right before entering, switch C you turn on and leave on. Get it? Switch C controls the "on" bulb when you enter, switch B controls the bulb that is off but still warm to the touch, switch A of course goes to the remaining bulb.

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