Match in the Bottle for a Kid’s Science Demonstration

This is a simple science demonstration that you can do with your kids. It deals with the physics of air pressure and the nature of water. It's fun, simple, clean, safe, and you can understand everything that goes on. You can have fun and be a tower of knowledge for your kids.

If you have young children of your own, then you probably did not see this demonstrated on "Watch Mr. Wizard" as I did when I was very young. In fact, this program was shown in black-and-white and you might not remember that. It was a great time for kids my age to become excited about learning. Mr. Wizard was Don Herbert who died recently and left a whole generation of people who had a better appreciation of learning than they might have had without him.

Here is what you do to make this work: You will need an empty tall bottle - such as a wine bottle, a tight fitting cork, and a wooden (not cardboard) match and some water. Some kind of investment, isn't it?

1. Fill the bottle up with water to the point where the sides start to constrict near the top.

2. Break the wooden match off less than one inch from the tip and drop it into the water. It ought to float vertically in a moment with the head pointing upwards. If not try other lengths until you get it to sit correctly. It might help to wet the match first.

3. Force the cork part way into the bottle.

4. As you force the cork the farther into the bottle neck you will see the match actually move toward the bottom of the bottle.

5. You can move the match up or down by changing the pressure on the cork. You can even get it to stop halfway down and rest in one place! If this were not a learning time, you would seem to be very great magician.

6. Eventually the wooden part of the match will water-log and the sulfur top will start to disintegrate so don't push your luck on this one.

So, here is what is happening in case you haven't figured it out for yourself. It's really just simply physics.

As anyone who drives a car with balloon tires knows, air can be compressed. In our case, you are using the same amount of air and squeezing into a smaller space with the cork. This creates an increase in air pressure which means that the air is pushing harder on the surfaces that are containing it. Now, the cork and glass are not going to compress to let the air return back to its original volume which it would like to do. But what about the water? Well, it so happens that water does not really compress either. However, there is one subtle place yet to be discussed where the air can find some relief from your pressure on the cork. Give up? Within the wood of the stick are a great many very small air pockets. As long as these pockets are the sizes they are, the match will float. If the pockets are somehow made to shrink, the match will eventually become denser than the water and it will sink. Are you catching on? As we said, water cannot be compressed; however it can be pushed and made to exert pressure on other things. What is happening here as you push on the cork and increase the air pressure in the top of bottle is the water is being forced to squeeze the match stick which responds by shrinking all the microscopic air spaces that are inside it. You cannot see it happen, but the match actually gets smaller as it becomes denser. As you continue to push on the cork, the water continues to exert an ever-greater force upon the match which becomes smaller -more dense - and eventually the match begins to descend in the water.

It looks like you are somehow pushing down on the match. However, you are actually squeezing it from all directions and making it smaller until it weighs more than a volume of water equal to its own size.

Pretty cool, eh?

Oh, by the way. Try it first when you are alone. Take it from a former science teacher; even the best demonstrations can go wrong and leave you looking like something other than a magician or genius.