Field Notes: Science experiments

I wanted to stop by and share one of my small collections of science experiments for kids. 

Science experiments are a wonderful way for kids to learn all about scientific principles and the world around them during tutoring.  These great experiments are fun, simple, and teach your tutee about the wonders of the interplay of forces.

1. The Impossible Bridge:
What you'll need:
3 plastic cups/glasses (make sure these are a heavy plastic for the best effect!)
A sheet of paper (I usually use paper from the printer)

Step One: Place 2 of the cups about 6 inches apart and lay the sheet of paper across them to form a flat bridge.  Put the third cup on the paper bridge.  What happens?
Step Two: Now take the sheet of paper and lay it in folds lengthwise, like you are making a paper fan or an accordion.  By the time you are done folding the paper, you should have several, small peaks that look like upside down "V" shapes from the front
(Like this: /\/\/\/\/\/\/\/\/\/\). 
Step Three: Lay the folded paper across the cups again.  Now place the third cup on the folded paper bridge.  What happens this time?

Why does it work?
Flat surfaces are always able to hold less weight, and resist less pressure and stress, than vertical surfaces.  So, when the paper is laid flat, it immediately gives way to the weight of the cup.  However, when the paper is folded, the weight of the cup is distributed evenly along the sloping vertical surfaces, making the bridge much more stable and a lot stronger. 

2. Stunt Ball:
What you'll need:
A clear jar
A marble (or small bouncing ball)

Step One: Put the marble on a table. Place the jar upside down over the marble, then tell your friend that you can easily carry the marble around the room with you, without even turning the jar over first.  Sound impossible?  Believe it or not, you can carry the marble in the upside down jar!
Step Two:  Start moving the jar in small rotating motions, so that the marble begins to spin along the inside walls of the jar.  As long as you keep moving the jar in a circular motion, the marble will continue to spin fast enough to "stick" to the interior walls of the jar as it moves.  You can then carry around the marble, even though the jar is still upside down!

Why does it work?
This experiment is all about centrifugal force.  As the jar rotates, the centrifugal force presses the marble against the inner walls of the jar, and keeps it from falling out of the open, upside down jar!

3. Twirling Egg:
What you'll need:
2 eggs - 1 raw and 1 hard boiled

Step One: Spin the raw egg first.  It will only spin slightly, mostly rocking back and forth before it topples over.
Step Two: Now spin the hard boiled egg.  What happens this time?  The cooked egg will not only continue to spin, but will stand upright like a top.

Why does it work?
The yolk is heavier than the white of the egg, so (thanks to centrifugal force) the yolk will roll to the side when you spin the raw egg.  This breaks up the spinning action and makes the raw egg rock more than it twirls.  The cooked egg, on the other hand, has a solid center of gravity that sits lower (towards the wider part of the egg), making it not only spin more smoothly, but also stay upright. 

4. Coin Traveling:
What you'll need:
3 coins (I like to use quarters for this trick)

Step One: Lay the 3 coins on a table, making sure that they are in a straight line.  Only 2 of the coins should be touching, while the third coin should be a few inches back from the group, towards you.
Step Two: Press down hard on the middle coin, and give the coin closest to you (the one away from the group) a solid flick so that it hits the middle coin.  The force of the strike should travel through the middle (pressed down) coin, and cause the third coin to shoot away from the group. 

Why does it work?
Believe it or not, solid bodies, in this case coins, have a lot of elasticity.  When the coins collide, they are instantaneously compressed, but spring back to their original shape just as quickly.  As this occurs, the impact from the coin striking the middle quarter is transferred to the third coin, causing it to shoot away from the other coins. 

- G.M., enthusiastic tutor from NYC