Candles are not only found in so many places, but they can grasp at so many things. From states of matter to thermal conductivity to combustion to light, it sometimes seems the whole scientific world can be found in a tiny flame.
Here are some candle experiments and explorations that I like to do with my classrooms for young and old alike!
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Step 1: Dissect a Flame
Let's dive right into the middle of it.
Cut a piece of metal mesh, and place it directly over the flame. Press down into the middle of the flame to dissect it. You can see into the dark center of the flame. Although this zone is sometimes called the hottest, but it is actually the coldest. This area is formed by unburnt wax vapor moving up into the area above the wick from capillary action.
You may notice lots of soot pouring out! The incomplete combustion suddenly releases these wax molecules into the air without being contained on all sides by the luminous part of the flame. Linked carbon chains rise and get stuck on the mesh, too.
The hottest part of the flame is the "aura" around the visible part of the flame, or the somewhat invisible shimmer. This is where complete combustion is happening. You can also easily see the yellow area, and if you look closely, the blue area at the base of the flame. This is caused by the incomplete combustion of carbon and the creation of low amounts of carbon monoxide.
So much in one flame!
Step 2: "Burn" a Nail?
Take a nail and put it into the flame. Turn it to collect soot on it. Is it burnt? What is that stuff? This causes a great debate in many classrooms as to whether the nail is burnt or not.
Combustion is a tricky thing to understand, and the chemical change of "burning" is, too. Fundamentally, when you burn it, you can't go back. You can burn toast, but you can't turn it back into bread. Use a paper towel to clean it off, and you'll find the nail was actually just collecting soot which came from incomplete combustion from the candle.
A secondary question with younger groups is what the liquid in the candle is. Many think it's water. An easy way to test this out is either to wait or to dip the nail in, and bring it out as solid wax. The wax just froze!
Step 3: Sawdust Convection
Grab a little bit of sawdust, and drop it into your pool of wax. You have to look closely, but the sawdust flecks will start to rotate along convection currents, coming to the flame, and launching away with heat.
Step 4: Thermal Conductivity
A candle is just the right amount of heat to test the thermal conductivity of different objects. Try out steel, aluminum, and copper to begin to see a large difference. Have students hold metal strips either in their hand or with tweezers for 10 seconds, and have them take the metal out. Which is hotter? Where has the heat spread to?
What could you do to a piece of metal to make it get hotter faster at the end? What about stay cooler longer? If you had to make a handle for a pan, what would you use?
Step 5: Three Little Jars
The combustion triangle needs oxygen, and a good lot of it.
Try placing three different sized glass jars over three candles and predicting which will go out first. A common misconception with this is that the area under the jar is completely out of oxygen when the flame runs out, but the reality is that candle combustion stops happening at about 30% oxygen levels.
A great modification on this is to try different heights of candles in the same area. You will find that the ones higher up go out first. More oxygen is hiding at the bottom, which is part of the reason (among others) that we are warned to stay low in a house fire.
Step 6: Extinguishing Breath
Ever thought you had bad morning breath? Such that light ceases to exist?
Candles go out much faster if oxygen is replaced by another guess. Hold your breath for 15-20 seconds, and then breath slowly into a glass jar. When you place the jar over the candle, it immediately goes out. It's an incredible thing to watch in such a C02 atmosphere.
Step 7: Chemical Extinguisher
Another C02 experiment is to combine baking soda and vinegar to "pour" over your flame. As you tilt the glass, the C02 cascades down and extinguishes the flame immediately. Neatly, C02 is used in one type of fire extinguisher for this reason. This is a great way to show that C02 is heavier than your typical air. Because of this, in a somewhat still room, even minutes after the chemical reaction, you can still extinguish the flame by tilting the jar.
Step 8: Thirsty Candle
This is a classic that you can find everywhere on the internet. The main attraction is absolutely that water gets sucked in to the jar when the flame extinguishes, but can you see what happens before?
If you look closely at the edge of your glass, there are tiny bubbles escaping. As the candle burns, it heats up the air and glass in the small environment, and as the gas expands, some of it escapes. As soon as the heat source goes away, in floods the water to fill a new low pressure zone.
Step 9: Pinhole Candle
A neat way to look at the interesting shape of a candle is through a pinhole camera. Cut two sheets of paper, one light and one dark. Make a pin-sized hole in the dark sheet, and hold it near the candle. Put the light sheet behind it, and you should be able to see the flicker of a now upside-down candle flame projected on to the back.
Step 10: Losing Weight
Where does the wax go? You start out with wax, and in the end, your candle appears smaller. Where does it all go? With a scale, you can measure your candle over time, and even graph out how much weight it's losing per minute. Is it an even curve, or does it change?
Step 11: Mini-Boiler
When waiting for dinner, it seems like boiling can take forever, but not at a small scale.
Make an aluminum foil bowl, and hold it over your flame for 10-20 seconds, and you'll see begin to boil. To add to the experiment, you can try the same with salty water (faster), or dyed water (leaves the dye behind). Additionally, with the addition of a little metal roof, you can catch the water that's evaporated and now condensating.
Step 12: Keep Exploring
There is so much to learn in a single flame. From combustion to heat to light, there are far more experiments than are listed here. Try looking around for the candle seesaw, lighting wax vapor, and more!
Have fun, be light, and happy learning.