Fire and Water.
You can make water draw up into a upside down glass, as though by magic.
Here’s what you need:
- Tealight candle (could also use a match broken and anchored with a coin)
- Small bowl
- Small glass
Here’s what you do:
- Set the candle (or broken match) in the bowl
- Add water to the bowl, until it is about half-way up the side of the candle
- Light the candle
- Set the glass gently over the candle, down in the water
What Should Happen
Within a few seconds, the flame on the candle will blow out.
In less than a minute after the flame goes out, water will be sucked up into the glass.
You can add food coloring to the water to see it more easily, but, with a white bowl and clear glass it was still easy to see this dramatic effect.
Why Is This Happening?
When the air inside the glass is heated up while the candle is lit, a vacuum of low pressure is created inside the glass.
As the air cools down again after the candle goes out, the air pressure on the water outside the glass pushes it up into the glass within minutes.
You can watch it happen on this video.
Within half an hour, all the water in the bowl had been sucked up into the glass, making the tealight candle float.
The next day, the water was still sucked up inside the glass, though I doubt if grandchildren could leave it undisturbed so long.
They could try variations, like how much water you can add to the bowl for this to work and what size glasses are most effective.
Does This Have Any Practical Applications?
A vacuum is also used in the production of freeze-dried coffee.
Coffee is brewed, frozen, laid out on drying trays and put into a vacuum tube.
By means of sublimation, with the help of the vacuum, moisture is drawn out of the frozen crystals as a vapor, leaving only the freeze-dried coffee behind.
Thanks to chemistry.about.com for this activity.
Carol Covin, Granny-Guru
Author, “Who Gets to Name Grandma? The Wisdom of Mothers and Grandmothers”