Gardner - Martin Gardners Science Magic: Tricks and Puzzles

An ancient toy called the Cartesian diver is a small hollow glass figure that moves up and down in a cylinder filled with water when pressure is applied or released to the air above the water. Heres an amusing way to demonstrate the same effect with two paper matches.

Youll need a plastic bottle with a tight-fitting cap. Fill the bottle to the brim with water; insert two paper matches, with heads down; and cap the bottle. If you now squeeze the sides of the bottle the pressure will force water into the fibers of the paper matches, causing them to sink. When you release the pressure, the matches rise. One match usually travels up and down ahead of the other. By adjusting the pressure, you can make each match move up and down as you please.

Magicians like to use matches with differently colored heads. Call one Mike and the other Ike. You can now make the matches respond to such commands as Come up, Ike and Go down, Mike.

Before showing this trick, secretly rub your wet index fingertip on a bar of soap.

Fill a shallow dish, a saucer will do, with water and scatter black pepper over the surface. The water represents a lake. The pepper grains are bathers. Your finger, you explain, models another bather entering the lake. So saying, touch the tip of your middle finger to the water at the saucers rim. Nothing happens to the bathers. Repeat this a few times to represent other bathers entering the water.

Now, you continue, along comes a gorilla who has escaped from a nearby zoo. Again, your finger models the gorilla as he enters the lake. This time, however, place the tip of your soaped index finger on the lakes edge. Instantly all the bathers flee to the opposite side!

Carefully open a fresh egg so that the two half-shells are as similar as possible. Check to make sure that the shell for the larger end has an air bubble inside. Most eggs do.

If the bubble is there, you can mystify a friend with the following stunt. Fill a tall glass with water. Give the shell without the air bubble to the friend, while you keep the other half-shell. Say nothing about the bubble.

Put your half-shell, open-side up, on top of the water, and gently push on the shells rim until the shell fills with water and submerges. As it sinks, the bubble will cause it to flip over and land convex-end up. Fish it out with a spoon and challenge your victim to duplicate the feat. When he tries, his shell stubbornly refuses to turn over.

Repeat a few times. After the last somersault, surreptitiously poke your finger into the shell to break the bubble. If your friend thinks your shell differs in some way from his, let him now try it with your shell. To his puzzlement, the shell still refuses to flip over.

Adime is on the table beside a glass of water. The glass must have straight sides. Hand someone a straw and say, Betcha cant pick up the dime with this straw and drop it into the glass.

Heres how you do it. Put a drop of water on the dime. With one end of the straw in your mouth, bend over so the other end of the straw presses vertically on the dime. When you draw in air, the dime will adhere to the straw, allowing you to carry it over to the glass and let it fall in.

Follow this with, Betcha cant drop the dime several inches to the table so it lands and stands on its edge.

Secret: Dip the dime in the water and push it against the outside of the glass near the brim. When you let go, the dime adheres to the glass, slides down the side to the table, and remains on its edge.

A Water Transfer

Glasses A and B are completely filled with water. B rests on two table knives, which in turn are placed across the brim of C. The bet is that you can transfer all the water from A to C without touching the glasses.

The secret? With a straw, blow vigorously at the spot where the brims of A and B touch. The air blast forces water out of A, between the brims of A and B. The water will drip down the outside of B and into C.

But how, I hear you asking, are you able to fill A and B? Simple. Just put the two glasses below the surface of water in a sink, press the brims together, and lift out!

Water Level Riddle

Float a small glass in a beaker filled with water, then add to the glass marbles, pebbles, or other small heavy objects, until the glass is close to sinking. Mark the water level on the beaker. Remove the glass, dump the marbles into the water, and refloat the empty glass. Will the water level rise or fall?

Few students will guess that the level will fall. It seems plausible that putting the marbles into the beaker would make the level rise.

Two Corking Good Challenges

Challenges

1. Pour water into a glass until it is almost full, and then drop a small cork on the surface. The cork will drift to one side. How can you make the cork stay at the center?

2. Fill a beaker or pan with water and float a cork on the surface. How can you make the cork sink to the bottom without touching it?

Solutions

1. Carefully add water to the glass until the surface becomes convex, rising slightly above the rim. The cork will move to the center or highest spot.

2. Hold an empty glass upside down over the cork and push it down. Air trapped inside the glass forces the water aside, allowing the cork to sink.

The Dancing Triangle

Pour boiling water in a large bowl until it is about half an inch (1 cm) below the rim. Cover it with a cloth napkin or handkerchief. (Silk cloth works the best.) On top of the cloth put a triangle, cut from very thin paper, such as tracing paper, or paper used for second sheets in typing with carbon paper.

The paper triangle comes alive. It will curl up, then slowly uncurl and curl the other way, and keep up this curling and uncurling as long as the water remains hot. Its slow ballet dance may make it crawl over the edge of the bowl, but you can keep this from happening by constantly adjusting the cloth.