Burning Both Ends

Have you ever heard the expression "burning the candle at both ends"? It means that someone is working very hard, usually without sleep. But I'll bet you have never seen what happens is you actually burn a candle at both ends!

This experiment involves both sharp knives and fire, so definitely have an adult help with it!

What you'll need:
Candle, as described below
Knife
Ruler
Long sewing needle
2 wine glasses
Matches or lighter
Newspaper

First, you have to find a candle that will work well. The best candles for this experiment are straight cylinders about 1/2 - 3/4 inches (1 - 1.5 cm) in diameter. Candles that get smaller near the top won't work as well. With a sharp knife, cut about 1 inch (2.5 cm) off the bottom of the candle, and dig out enough wick that you can light it. Trim the candle so that the bottom looks very much like the top. Measure the length of the candle and make a mark in the exact center. Push a long sewing needle through the middle of the candle from one side to the other.

Spread newspaper or other absorbent paper on the surface you will be working on. Position the two wine glasses next to each other at a distance slightly larger than the candle diameter. Balance the needle on the glass rims, so that the candle acts like a seesaw (see diagram). It is best if the candle is well-balanced enough that it is horizontal, but the experiment will also work if the candle is at an angle. Light both wicks and watch what happens!

With both ends of the candle burning, wax drips from the top and bottom. When a drop falls from the top of the candle, it becomes lighter, and tips upwards. Then a drip falls from the bottom, and that part tilts up. You will see the candle start to rock back and forth, just like a seesaw. The rocking will get stronger and stronger. If the candle isn't perfectly balanced, the rocking may slow down, or even stop, but it will start up again.

So now you know what happens when you burn the candle at both ends!

Make A Wish!

Do you like to blow out candles on your birthday cake every year? Did you ever wonder why on earth we put candles on a cake? And why we're told to "make a wish" as we blow the candles out?

This tradition is actually thousands of years old. It comes to us from the ancient Greeks, who decorated cakes baked as offerings to their gods with candles. They thought this made the cakes shine like the moon. In the Middle Ages, people would bake small items, like rings, into cakes. It was believed that good luck would come to the person who got the slice with the the surprise in it. Different countries celebrate birthdays in different ways; some of these traditions are described here.

In earlier times, people believed that the smoke from the blown-out candles would carry any prayers or wishes into the skies where the gods lived. This would make it more likely that they would hear (and hopefully answer) the requests. What do you think? Do your birthday wishes usually come true?

Blowin' In The Wind

How do you usually extinguish a candle? Not by putting a glass over it, but rather, by blowing it out. Why does this work?

Maybe it's that carbon dioxide again. Your exhaled breath contains more carbon dioxide than the air you breathe in. When you blow out a candle, do you reduce the amount of oxygen around the flame so that it goes out? No - there's still more oxygen (about 15%) in your exhaled breath than CO₂ (4-5%). That's not enough to snuff out the flame. The real explanation is actually simpler. The candle will go out if you blow hard enough to separate the flame from the wick. If the molten wax isn't actually on fire, it can't continue to burn.

How Does A Candle Work?

Candles are amazing sources of light, which have been used for centuries. They are deceptively simple - a candle appears to be a string (the wick) stuck into a chunk of wax. You might think that any old piece of string will act as a wick, but that won't work. If you tried using the wrong kind of string (or the wrong kind of wax), you would find that the flame would go out quickly, and the candle wouldn't continue to burn. If you watch a candle for a while as it burns, you will notice that the wick doesn't actually burn away, and it's the wax that disappears.

The wax must melt into a fairly thin liquid that can be soaked up by the absorbent wick. Two kinds of wax that do this are paraffin and beeswax. Paraffin is made from crude oil; beeswax comes from bee hives. The wax is absorbed into the wick where it vaporizes, then burns. If you watch a candle closely, you'll see that the wick burns much, much slower than the wax. When you blow out the candle, you see a white stream of smoke; this is cooling wax vapor. Ask an adult to touch a match to this white stream; you should see that the candle relights as the flame travels down the column of wax vapor.

SAFETY FIRST!

Candles are very common objects, but they can actually be used to demonstrate a lot of different scientific principles. This month, you'll learn how candles work and do several candle-based experiments. However, there is one very important rule to be followed in every experiment this month. DO NOT DO ANY OF THESE EXPERIMENTS WITHOUT CAREFULLY READING THE SAFETY INFORMATION FIRST!