Why Does Water Rise? Best Science Experiments with Water for Kids! Looking for one of the best science experiments for kids? Try this popular “Why Does Water Rise?” experiment and incorporate some TECH to prove the science.
It’s like magic and kids love watching this fascinating science experiment, but what is actually happening when you place a glass over a lit candle in a bowl of water? I set my two little scientists the task of finding out. And if you are looking for an awesome science fair idea, in our opinion this is a winner!
Why Does Water Rise? Vacuum Science and STEM Activity
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Check out our video of this and you’ll know why you have to try this yourself.
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Supplies and Tools
A shallow bowl or dish
Water (adding a few drops of food coloring makes it easier to see what is happening)
A large glass jar (we used a flower vase)
And if you have budding scientists you will also need a non-contact infrared digital thermometer. This is a fantastic way to bring in some technology to your science and make the leap into STEM activities.
Set your candle on the plate and pour approximately 1/2 to 1 cup of water on the plate. Light your candle, then place your jar (or vase) upside-down over the candle.
Then sit back and watch one of the best science experiments ever!
My youngest thought it was magic, and both my kids were amazed.
As the candle goes out, all of the water is sucked up into jar. The water rises! But why does water rise?
Very quickly my oldest assumed it had to do with the burning candle using up all the oxygen because the water would rise as soon as the candle went out. He hypothesized that the lack of oxygen was causing a change in the pressure inside the jar.
He was right that the candle went out because it ran out of oxygen, but that isn’t what causes the water to rise according to our friends over at Harvard.
It was time to break out the non-contact digital thermometer.
We did the experiment again and this time my oldest took temperature readings.
Very quickly the numbers climbed to over 23 degrees Celsius as the candle burned inside of the jar.
But as the flame weakened the temperature numbers started dropping. Then the candle went out and the water started climbing. The faster the water climbed the faster those numbers dropped. Overall it lost 2 degrees in a matter of seconds.
The vacuum created was so strong it sucked up all the water and even created bubbles as it sucked in air too once it had pulled in all the water from our plate.
Alter how much water you use. How does it affect your results? What is the maximum amount of water your set up can suck up?
Now change your glass container to something bigger or smaller. How does that affect your results? (Hint we found a narrow neck gave us the best demonstration of water rising.)
Does changing your candle for a bigger or smaller one affect the results?
How does changing the temperature of your water affect the results?
This is one of the best science experiments because it demonstrates what happens to a flame as it runs out of oxygen and also how a rapid temperature change can create a vacuum or suction by altering the air pressure inside the jar. Not to mention it’s like magic! Bound to impress, especially at that science fair. And with all the adaptions and variables you can alter, you can make this traditional activity, uniquely yours.
Bonus Science Experiment
On a clean plate place a lit candle and cover with the jar. Once it goes out, gently lift the jar and relight the candle. Try to place the jar over the candle.
What happens? The candle immediately goes out!
Because the air in the jar is still lacking oxygen because it was all burned off. Blow in the jar a few times or move it around to replace the oxygen, then try again. Once you replace the depleted oxygen in the jar you can position it over the candle again and it will stay lit until it burns off all the oxygen again.
This was a great little side demonstration. Even though we couldn’t see it, the chemical composition of the air inside of the jar is changed by the burning flame and it takes time and air movement to bring oxygen back into the container. A fantastic way to show that even though we can’t see it, science is happening all around us.