This experiment is a classic that many are sure to know. But above all the question is interesting, why this Water rises in the glass. Is it just how often it is claimed that the oxygen consumed? Or is there more behind it? (More experiments with water)
What is needed for this experiment?
- a plate about 1 cm high filled with water
- a tall, narrow glass
- a tealight and fire
- possibly another coin
What to do in this experiment?
For this experiment, take the burning tea light, put it in the Plate with water and put the glass over the candle. You can also do this experiment with a little less water and put a coin in your plate. In the end, the coin can be taken out of the plate (almost) without the hands get wet.
What happened in this experiment??
This question is answered very differently. You can usually hear the following explanation: The candle consumes the air and therefore water rises into the glass.
However, this explanation cannot be correct because the candle consumes oxygen but only converts it into something else.
If the candle burns, carbon dioxide and water are produced in the form of water vapor. For this reason, the glass often fogs up during this test. This mixture actually takes up less space than oxygen. Carbon dioxide also dissolves well in water, so that there is also some space in the glass for the water. But this alone cannot be the reason why the water in the glass rises so high.
What seems more important is the fact that the air in the glass warms up, expands and escapes from the glass. If you put the glass quickly and from the side over the candle, it bubbles even in the plate. This is different if you slowly lower the glass from above over the candle. Then the air is already heated as the glass moves down. It expands and escapes before the glass even touches the water. Bubbling can then no longer be observed. If the air in the glass cools down and its volume is reduced, a negative pressure is created.
The question of how exactly the water gets into the glass is also interesting. The escaping air creates space that the water fills. However, the water is not sucked into the glass, but pushed into the glass by the greater external air pressure.
The term “pressure” means a force on a certain surface. The greater the force and the smaller the area, the greater the pressure. A needle on the skin is much more uncomfortable than a nail with the same force. Air pressure is the force that an amount of air or so-called air column exerts on a surface.
This everyday phenomenon
Differences in pressure go hand in hand with strong forces. This is also the reason why the cabin’s internal pressure is reduced after take-off. This is the only way to prevent the forces on the fuselage from becoming too great.
Otherwise, the power of air pressure can also be experienced with suction cups, and this is everywhere – not just in the home. They are widespread in nature – octopuses and snails are certainly the best known examples. But they are also used in many technical applications. A suction cup holds because there is a vacuum between it and the surface to which it adheres.
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