Floating balloon

Without the addition of the glass beads, the balloon would rise in the glass of water. If you put the balloon into the water, it slowly sinks to the bottom (picture above).

After adding table salt, the balloon rises and "floats" in the water (picture below).

Fill the beaker about ¾ full with water. Place 5-6 glass beads in a balloon. Then fill the balloon with water. Squeeze out the excess air and tie the balloon closed. Now place the sealed balloon in the beaker filled with water. Then dissolve some table salt in the water.

• 1 beaker (1000 ml),
• 2 balloons,
• 5-6 glass balls (diameter about 5 mm, or other material that sinks in water),
• some table salt,

Instead of the balloon, you can also use a raw egg, which must not be too old. (As it ages, a gas bubble forms which makes the egg float in water).

What is technically behind the experiment

The density of water increases when salt is dissolved in it. 1 ml of salt water solution is therefore heavier than 1 ml of pure water. The more salt is added to the water, the greater the buoyancy, which is equal to the weight of the amount of liquid displaced by the balloon. If the buoyancy and the force of gravity acting on the balloon are equal, the balloon begins to "float" in the water.

What the experiment has to do with everyday life

Many children are familiar with the fact that it is easier to swim in salt water (in the sea) than in fresh water (swimming pool). This phenomenon can be used to describe the experiment.

The following variant is suitable as preparation for the experiment described above: By preparing balloons appropriately, you can ensure that one balloon floats, another floats and a third sinks. The attempt to recreate something like this leads to the realization that more water in the balloon does not cause it to sink. So the weight of a body alone does not determine whether it floats or sinks.

Martina Strüning