Water floating in water
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Experimental observations
The rubber rings relax more and more the deeper the bottle is immersed. When immersed in water, the bottle can be moved almost "powerlessly".
Carrying out the experiment
Attach the rubber rings to the bottle as shown. Now hold the bottle by the rubber rings and slowly dip it into the container.
experimental setup
- a small plastic bottle filled to the brim with water,
- two rubber bands,
- a thread,
- a large container of water (e.g. a bucket),
Explanations for the teacher
What is technically behind the experiment
This experiment impressively demonstrates that a body that sinks in water also experiences buoyancy. Archimedes' principle states that the buoyant force of a body in water is as great as the weight of the liquid displaced by the body. The further the bottle is immersed, the more water is displaced and the more buoyancy the bottle experiences. The buoyancy force counteracts the weight force. This is why the bottle appears to become lighter when it is immersed. When the bottle is fully submerged, it displaces about as much water as it contains. The buoyancy and the weight of the bottle roughly balance each other out. If a body has a density that is the same as the density of water, then buoyancy and weight are equal and the body floats in water. Applied to water, this means that water floats in water. Water that is warmer than the surrounding water has a lower density and rises.