Rising Water

Try this fun experiment with candles, air and water. Isn’t it amazing that air pressure can cause water to rise and climb the inside of a glass?

Equipment

• A plate
• Water
• Food colouring
• A tea candle
• Matches
• A glass or an Erlenmeyer flask with an opening larger than the candle

Instructions

1. An adult should help with this experiment
2. Pour a little water onto the plate and add some food colouring. The water should cover the bottom of the plate and climb up the sides
3. Light the tea candle and place it in the middle of the plate
4. Hold the candle over the tea candle for a few seconds, ensuring that the air inside the glass is heated
5. Place the glass on the plate over the candle
6. Watch as the flame is extinguished and the water rises in the glass

What happens?

The air inside the glass expands when it is heated. This causes some of the air that was inside the glass to be pushed out. The air gets cool again when the flame is extinguished, which leads it to shrink and occupy less space inside the glass. Now the air pressure inside the glass is lower than outside. The air pressure outside the glass pushed the water. This is why it rises in the glass.