The hot air balloon

After a while, the yellow bag spreads out and, after you let go of it, rises up to the ceiling. However, it does not stay there, but falls back to the floor.

The hotplate is switched on and the cardboard tube is placed over it. When you can feel the very warm air above the cardboard tube with your hand, the yellow bag is placed over it.

• Hotplate,
• cardboard tube,
• Yellow bag,

• You must make sure in advance that all materials are in good condition.
• The yellow bag must not be too close to the hotplate, otherwise it could start to burn.
• The cardboard tube must allow air to pass through from below.
• The hotplate must generate enough hot air.

What is technically behind the experiment

This process can be compared to the buoyancy of a body in water. The hot air contained in the hot air balloon has a lower density than the cold outside air. The buoyancy force is always as great as the weight of the displaced (cold) air volume. If there is sufficient heat, the upward buoyancy force is greater than the downward weight of the bag and the hot air it contains. The bag then rises.

What the experiment has to do with everyday life

We also encounter this physical phenomenon of warm air rising in everyday life. A Christmas pyramid, for example, could not turn without the warmth of the candle flame. The candle flame heats the air, which rises upwards and causes the wooden wings of the pyramid to turn. Another example of this physical phenomenon is gliders, for whom the term "thermal" is very important. They use it to gain height in the air. They exploit the rise of warm air.

Stephanie Csernar