RISING WATER SECRET

• Rising Water Secret Experiment
• Take it Further!!
• Take it Even Further!
• Science Fair Connection

A common misconception regarding this demonstration attributes the rising water to the consumption of oxygen (O2) in the air trapped inside the flask. Truth is, there is a possibility that there might be a small rise in the water due to the flame using up the oxygen, but it is a very small volume compared to the heating (expansion) and the cooling (contraction) of the gases within the flask by the candle. Simply put, if the oxygen being consumed were the main contributing factor, the water would rise at a steady rate inside the flask as the candle flame got smaller and smaller. Instead, the water rises rapidly after the flame goes out.

Did you see bubbles coming from the flask as it entered the water? If not, redo the demonstration except this time, lower the flask into the water faster and watch the rim closely as it enters the water. As the flask is lowered, the candle flame heats the air trapped in the upside down flask. This hot air expands rapidly and pushes outward in all directions. Some of the hot, expanding air is pushed out of the opening of the flask and you see it as bubbles if the rim is below the water level. The candle burns dimly for a short time until the oxygen is gone. When the flame goes out, the air in the flask quickly cools and contracts (takes up less space). The cooling, contracting air creates a vacuum (a lower pressure) in the flask. Lower pressure inside and higher pressure outside means the water is pushed up into the flask until the air pressure inside is equal to the air pressure outside the flask. You might be thinking, “The vacuum sucked the water into the flask.” That’s sort of the right idea but scientists don’t like to use the term “suck” when describing the effects of a vacuum. Instead, they’ll explain it as, ”Gases exert a push from an area of high pressure into an area of low pressure.” So actually, nothing ever sucks – not straws, not vacuum cleaners, not even black holes. Things are only being pushed or pulled by differences in pressure or forces. Wow! Who knew?!

The demonstration you started with at first has now become an experiment. What’s the difference? Well, now you’ve asked a question that requires an experiment to answer it: What happens to the water level in the flask if the amount of heat is changed? You started researching an answer by using less heat. Everything else remained the same; the only thing you changed was using a smaller candle to produce less heat.

What you saw should not have been a surprise. There were bubbles as before and the water rose in the flask as before. You expected the candle to go out but you may not have expected it to be under water! Notice that the flame probably died before the water even reached the wick but the water continued to rise even after the candle was submerged. Notice something else: the water level in the flask is not as high as in the demonstration. Since everything else was the same, you can say that less heat causes less air to be pushed from the flask which means less water will be needed to equalize the pressure and the water level will be lower. Oh, darn, you may have to repeat this test several times to verify your initial results and confirm the data you’ve collected.

By using three small candles, you effectively tripled the amount of available heat inside the empty flask. The air inside the flask was heated to a higher temperature than the test using one small candle. As a result, much more air was pushed out of the flask as the air expanded. This meant that as the air cooled and contracted after the candles went out, the pressure dropped lower than in the first test so more water was needed to fill the flask to equalize the air pressure. You saw that result when the water rose to a higher level.

Science Fair Connection

Observing and discovering the Rising Water Secret is pretty cool, but the demonstration isn’t a science fair project, yet. You can make it one simply by identifying a variable (something that might change the outcome) in the experiment (like using more or less heat), then testing that variable (as you did), and correctly reporting the results. Think about some variables like these that you might test:

• Test different diameters of the opening for the container you put over the candle. How does the size, shape, or volume of the container change the results? What’s the best water temperature to have so you achieve the highest level inside the container?
• How does changing the water level in the pan affect the outcome? How can you achieve a suction strong enough to allow you to pick up the whole apparatus just by lifting the container after the candle goes out?

These are just a couple of ideas, but you aren’t limited to them! Come up with different ideas of variables to test and give them a try. Remember, you can only change one variable at a time for each test. For example, if you are testing different water temperatures, make sure that all other factors in the test remain the same!