Physics

Gilla:		Dela:

Video

Materials

• 1 balloon
• 1 candle
• 1 matchbox or lighter
• Water
• Safety equipment: 1 fire extinguisher

Short explanation

The balloon doesn't burst because the water in it absorbs most of the heat from the candle.

Long explanation

Without water in the balloon, the heat from the flame would break the balloon's molecules apart and it would pop. But when there's water in the balloon, the heat spreads immediately from the balloon to the water. The heated water then rises and is replaced by colder water. And so it continues.

But what is this "heat"? Well, the higher the temperature of a substance, the more the particles (atoms, molecules or ions) that make up the substance move. If the substance is a gas or a liquid, the particles can move as they wish, but if the substance is a solid, the particles mainly vibrate in their place.

When the candle burns, gaseous chemical substances with very high temperatures form. The particles that make up these gases collide with the particles of the balloon and set them in motion. Should the balloon's particles (molecules) become too hot, the bonds between them would break and the balloon would pop. But the balloon's particles collide with the water's particles and set them in motion. This reduces the movements of the balloon particles - i.e. the heat is spread to the water.

When the particles of water (water molecules) move a lot, they end up far apart. This is because they collide so violently and often with each other. This means that hot water has a lower density than cold water. Therefore, hot water rises.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What happens if you have more water in the balloon?
• What happens if you use some other liquid instead of water?
• What happens if you hold the balloon over the flame for a longer time?

Gilla:		Dela: