What you need:
Water, a tall narrow glass, some food or poster colours, a candle (that is broad enough to stand on its own but still able to fit completely inside the glass), a dish, a matchbox
What to do:
1. Fill some water in the dish (about an inch deep). Add the colour to the water and mix well.
2. Place the candle at the centre of the dish. Light it.
3. Turn the glass upside down and place it over the candle, inside the dish. The bottom of the glass should not touch the candle’s wick. The top of the glass should be in the coloured water.
What happens?
Once the glass covers the candle, water starts rising up slowly inside the glass. The candle soon goes out and the water level inside the glass rises quickly.
Why?
As the candle burns, it heats up the air inside the upturned glass. Hot air expands and pushes against the walls of the glass. Thus the push of the air, or the air pressure inside the glass is high while the candle burns.
But then the flame gets snuffed out because there isn’t enough oxygen under the glass to keep it going. When this happens, the air starts to cool down and contract. This contraction of air lowers the air pressure inside the glass. When this happens, the air outside the glass tries to rush in to fill up the empty space and equalize the pressure. But the water in the dish gets in the way and gets shoved into the glass. The water stops rising when the empty space left by the contracting air is filled and the air pressure outside the glass and inside becomes equal.
Picture Credit : Google
