The bottle volcano

The hot, colored water immediately flows out of the small bottle like lava from a volcano and begins to spread over the surface of the tub. At the same time, cold, clear water flows into the inside of the bottle. Small eddies can be seen in the bottle. As the experiment progresses, the speed and intensity of the colored water flowing out of the bottle decreases. The colored water, which initially spread out on the surface of the water, sinks again after a while and begins to mix with the rest of the water.

First fill the tub with cold water. Attach the string to the neck of the small bottle. Now fill the small bottle with some red food coloring (or ink) and fill it up with hot water. Now use the string to slowly lower the small bottle to the bottom of the tub filled with cold water.

• a tub or a transparent shot,
• a small bottle of
• hot water,
• cold water,
• red food coloring or ink,
• a piece of string,

First of all, it can be said that this experiment is rather unproblematic, but very spectacular. This means that both the pupils and the teacher can observe a great deal in this experiment and demonstrate important physical processes. However, care should always be taken when handling hot water. It is very easy to get scalded. Instead of the bottle attached to the string, this experiment can also be carried out very well using a small preserving jar with a screw cap. Put some food coloring or ink in the jar, fill it up with hot water and close it with the screw cap. Then place the jar in the tub filled with cold water and open the screw cap.

What is technically behind this experiment

Water consists of tiny particles, the molecules. Heat accelerates their movement so that they move away from each other. The colored, hot water is thus less dense and therefore lighter. It therefore has a lower density and therefore greater buoyancy and rises upwards. It therefore "floats" on the cold water. The volume in the bottle freed up by the hot water flowing out is balanced out by the cold water flowing in. As the cold water flows in, the temperature of all the water in the bottle drops. At the same time, the temperature of the water in the tub rises (due to the hot water flowing out). Therefore, a slower progression of the experiment can be observed. Only when the temperature of the "hot, floating" water has cooled down to the same temperature as the rest of the water does it sink and mix with it. Under the influence of heat, water expands, becomes lighter and rises in colder water.

What the experiment has to do with everyday life:

If you transfer the explanation of this experiment to everyday life, you could ask yourself, for example, how water heats up in a pot. Pots are usually made of metal, which is a good conductor of heat, i.e. it can easily absorb and release heat. The pot is heated by the flame and in turn heats the water at the bottom of the pot. The warm water rises to the top, cold water takes its place, heats up and also rises to the top. This upward and downward movement of the water, known as convection, distributes the heat throughout the water. The effect of heat also plays a major role in the oceans. The oceans are constantly crossed by warm and cold water currents, real rivers, which influence marine life and the earth's climate. They are caused by winds and differences in temperature and salinity. Cold water (denser and heavier) from the polar seas flows at the bottom of the oceans, while warm water (less dense and lighter) from the tropical seas and the equator flows at the surface.

All experiments that demonstrate the effects of heat on water are generally suitable for this experiment. For example, the experiment "The floating hot water bottle" could be carried out very well in this context.

Julia de Groot