Thursday, April 6, 2017

STEM Experiment- The Thirsty Candle/Rising water secret


I honestly don't know what the actual name of this experiment is
but I heard someone refer to it as the thirsty candle or Rising Water Secret.
Here is an experiment that I saw in my 3rd grade science fair and forgot about.
Until Scouting University, where they did the experiment in a Nova class I took!
So for Spring Break, I allowed my son to do it.

Note: This uses dye. My son spilled the watered dye on our light counters in the kitchen.
It took a lot of bleach to get off. Please put plate in something so that it doesn't spill. Or use an aluminum tray instead of the plate.

Ok, so what you need is:
1 candle
1 plate or aluminium tray
water
dye
lighter/matches
clear glass

Experiment
1. Adult Supervision because of the matches or lighter.
2. Fill a cup with water, doen't need to be a lot.
3. Add 2 or 3 drops of food coloring to the water. My son used the gel stuff and gave it a good squeeze.
4. Pour the water into the plate or pan and place the candle in the middle of the water.
5. Light the candle.
6. Cover the candle with the clear glass and think about what is taking place both inside and outside of the vase. What invisible thing is
inside the vase? Carefully observe what happens to the water around the vase. It's bubbles a little. What happens to the candle flame?
It goes fast, so you may want to do multiple times. We did it once and then searched for answers. Apparently it wasn't as cool as the Elephant toothpaste, according to my son.



What Is actually happening?
How Does It Work?
The candle flame heats the air in the vase, and this hot air expands. Some of the expanding air escapes out from under the vase —
you might see some bubbles. As the flame goes out, the air in the vase cools down and the cooler air contracts and creates a
vacuum. This imperfect vacuum is created due to the low pressure inside the vase and the high pressure outside of the vase. We
know what you're thinking; the vacuum is sucking the water into the vase right? You have the right idea, but scientists try to avoid
using the term “suck” when describing a vacuum. Instead, they explain it as gases exerting pressure from an area of high pressure to
an area of low pressure.
A common misconception regarding this experiment is that the consumption of the oxygen inside of the bottle is also a factor in the
water rising. Truth is, there is a possibility that there would be a small rise in the water from the flame burning up oxygen, but it is
extremely minor compared to the expansion and contraction of the gases within the bottle. Simply put, the water would rise at a
steady rate if the oxygen being consumed were the main contributing factor (rather than experiencing the rapid rise when the flame
is extinguished).
*This information was sent to me by one of the SHAC STEM guys out of Brazos.

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