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How does a thermometer actually work?
It rained all day today. Nevertheless, I wanted to play outside with Mika. So I put on my rain jacket and we went outside and jumped from puddle to puddle. It was really fun. But afterwards there was some mud in my hair and Mika’s fur was also very dirty. When we got back home, I wanted to take a bath so we could warm up and get Mika’s fur and my hair clean again. I used a thermometer to check that the water was the right temperature.
At first, the water was still too cold, and the bar on the thermometer was right at the bottom. Then I set it warmer and the bar on the thermometer rose. But how does the thermometer actually know how warm it is?
After Mika and I had taken a bath, we researched how a thermometer works. The thermometer contains a liquid. Often mercury or coloured alcohol. Liquids expand when it gets warmer and contract when it gets colder. When the liquid in the thermometer expands, it takes up more space and the bar rises. The thermometer then shows a higher temperature. When it is cold, the liquid contracts. It then takes up less space and the bar drops again. The thermometer then shows a lower value.
Water also expands when it gets warmer. This could become a problem in the future. Climate change is also causing the oceans to warm up. This means that they are expanding. Sea levels are rising not only because of melting ice, but also because of the expansion of water.
Surprisingly, not only liquids, but also gases and even solids such as metals expand when it gets warmer. For example, the Eiffel Tower in Paris is several centimeters taller in summer, when it is warmer, than in cold winter. So the Eiffel Tower can grow and shrink, so to speak. I find that really exciting!