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Leaning fire

By David, 1 November 2018 Activity

Water in a cup sloshes around if you don’t move it carefully. What about fire? Let’s find out!

Safety: This activity involves fire, so ask an adult to help. Don’t do this activity during a fire ban.
First aid: If you burn yourself, blow out the candle and run the burn under cold water for 20 minutes.

You will need

• Small glass jar
• Tealight candle
• Blu Tack or other adhesive putty
• Long matches or lighter
• Bucket of water

What to do

1. Put a small blob of Blu Tack on the bottom of the unlit tealight candle, and stick the candle inside the jar.
2. Check that you can reach the candle safely with an unlit match or lighter. If you can’t reach the candle, try a smaller jar, or a longer match or lighter.
3. Go outside and find a clear area away from anything flammable.
4. Get a bucket of water ready. The water can be used to extinguish flames, in case something accidently catches on fire.
5. Carefully light the candle. If using a match, extinguish the match safely in your bucket of water after the candle is lit.
6. Wait for a minute or so until the flame is stable.
7. Before you do the next step, read it and guess what is going to happen.
8. Hold the jar in one hand. Watch the flame closely and move the jar quickly to the side. Did the flame lean over to one side?
9. Repeat the move several times. Does the flame always lean in the same direction? Was it the direction you expected?
10. When you’re finished, extinguish the candle safely.

What’s happening?

When I did this activity, I found the flame moved in the same direction as the jar! That’s exactly the opposite of what I expected to happen.

Imagine the jar is half full of water. When you move it fast, the water will move to the back of the jar. (You can even try this out to make sure!) So why does the flame go the other way?

Inside the jar there is a candle with a flame. But there’s also something else you might not think of: air.

Air doesn’t weigh a lot, but neither does a flame. In fact, air is denser (has more weight packed into its volume) than flames. That’s why flames point upwards.

When you move the jar, the air moves to the back of the jar. The lighter flame floats on top of invisible air, and gets pushed the other way. That’s why the flame moves forward, the same way you push the jar!

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