Top 10 Martin Gardner Physics Stumpers

Martin's earliest interests included astronomy and science, especially physics, and he also loved science fiction. In his memoirs (see pages 13–14), he reveals that he was familiar with Hugo Gernsback's Science and Innovation magazine as a boy in the 1920s. He also adored the fictional works of H. G. Wells and Jules Verne, and many decades later, the works of Isaac Asimov, who became a good friend.

When Martin started attending the University of Chicago, in 1932, his plan was to transfer to Caltech, in Pasadena, CA, after two years, to study physics. However, as result of his growing interest in philosophy, he ended up staying in Chicago to pursue that instead.

Martin always loved basic science experiments and tricks, and was fascinated with more general physics, the solar system, and outer space. He wrote several science puzzle collections aimed at young readers, as well as penning significant and popular books on special relativity and symmetry.

In later life, Martin came to know Carl Sagan and Roger Penrose personally. In his memoirs, he remarks, "I had the honor of writing the foreword to [Penrose's] Emperor's New Mind." He also reviewed major works by Penrose and Hawking. For his writings on physics, he received some notable awards.

The list to follow is offered purely in a spirit of fun and education, and is not intended to be definitive. It concerns only the most basic physics concepts, and nothing electronic. We gratefully acknowledge input from physicist Paul Camp; but he's not to blame for the final selections made.

No answers are offered. Remember the wise words of Bob Crease in Physics World (Oct 2014):

"Googling is not the Gardner way. The Gardner way is to ignite your fascination
so that you experience the pleasure of finding the answer yourself."

These stumpers have provided much pleasure for several generations of people, all over the world. If you're joining their ranks for the first time, welcome.

Many of these items appeared in Martin's Aug 1966 "Mathematical Games" column in Scientific American; the rest appeared in other columns or books of his. There is no particular significance to the order in which there are listed.

Top 10 Martin Gardner Physics Stumpers

  1. Upon Reflection

    Why does a mirror appear to reflect left right and not up down?
  2. Iron Torus

    A piece of solid iron in the form of a doughnut is heated. Will the diameter of its hole get larger or smaller?
  3. The Colliding Missiles

    Two missiles speed directly toward each other, one at 9,000 miles per hour and the other at 21,000 les per hour. They start 1,317 miles apart. Without using pencil and paper, calculate how far apart they are one minute before they collide.
  4. Magnet Testing

    You are locked in a room that contains no metal of any sort (not even on your person) except for two identical iron bars. One bar is a magnet, the other is not magnetized. You can tell which is the magnet by suspending each by a thread tied around its center and observing which bar tends to point north. Is there a simpler way?
  5. Melting Ice Cube

    A cube of ice floats in a beaker of water, the entire system at 0 degrees centigrade. Just enough heat is supplied to melt the cube without altering the system's temperature. Does the water level in the beaker rise, fall, or stay the same?
  6. Bathtub Boat

    A small boy is sailing a plastic boat in the bathtub. It is loaded with nuts and bolts. If he dumps all this cargo into the water, allowing the boat to float empty, will the water level in the tub rise or fall?
  7. Two Hundred Pigeons

    An old story concerns a truck driver who stopped his panel truck just short of a small, shaky-looking bridge, got out, and began beating his palms against the sides of the large compartment that formed the back of the truck. A farmer standing at the side of the road asked him why he was doing this.

    I'm carrying 200 pigeons in this truck, explained the driver. That's quite a lot of weight. My pounding will frighten the birds and they'll start flying around inside. That will lighten the load considerably. I don't like the looks of this bridge. I want to keep those pigeons in the air until I get across.

    Assuming that the truck's compartment is airtight, can anything be said for the driver's line of reasoning?

  8. Balloon in Car

    A family is out for a drive on a cold afternoon, with all vents and windows of the car closed. A child in the back seat is holding the lower end of a string attached to a helium-filled balloon. The balloon floats in the air, just below the car's roof. When the car accelerates forward, does the balloon stay where it is, move backward, or move forward? How does it behave when the car rounds a curve?
  9. Hollow Moon

    It has been suggested that in the far future it may be possible to hollow out the interior of a large asteroid or moon and use it as a mammoth space station. Assume that such a hollowed asteroid is a perfect, nonrotating sphere with a shell of constant thickness. Would an object inside, near the shell, be pulled by the shell's gravity field toward the shell or toward the center of of the asteroid, or would it float permanently at the same location?
  10. The Can of Soda

    Assume that a full cylindrical can of soda has its center of gravity at its geometric center, half way up and right in the middle of the can. As soda is consumed, the center of gravity is initially lowered. When the can is empty, however, the center of gravity is back at the center of the can. There must therefore be a point at which the center of gravity is lowest.

    Knowing the weight of an empty can and its weight when filled, how can one determine what level of soda in an upright can will move the center of gravity to its lowest possible point?

    To devise a precise problem assume that the empty can weighs 1.5 ounces. It is a perfect cylinder and any asymmetry introduced by punching holes in the top is disregarded. The can holds 12 ounces of soda, therefore its total weight, when filled, is 13.5 ounces.

    (The answer here has a bearing on a stunt in which a partially full can is balanced on its edge.)

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