Why Does Water Rise?
The flame on the candle needs the gas oxygen to keep burning. Once we place the glass container over the lit candle, the oxygen inside begins to get used up. Once all the oxygen has been used, the flame will go out. However, there are still other gases remaining inside the glass (nitrogen, argon, carbon dioxide, etc.). But these gases have lower pressure inside the glass when compared to the higher atmospheric pressure on the outside of the glass. This higher atmospheric pressure from the outside pushes the water from the plate up and into the glass. One more thing is happening here to make the water rise into the glass. When we cover the lit candle with the glass, it heats the air inside the glass. The heated air expands. As it expands it comes out from under the glass container. You might observe some bubbles after you put the glass over the candle. That’s the hot air escaping. Once the flame dies out, the air inside the glass begins to cool down. As it cools, the air contracts inside the glass container. This contraction pulls the water from outside on the plate into the glass.