Examine the construction of the self-made thermometer shown in the photo and describe its working principle. Do the same yourself. Answer the questions.
In the thermometer shown in the picture, the "working body" is air. As the air expands, it pushes the water out of the bottle, we see this as a rise in the water level in the glass tube. The thermal expansion of the liquid itself does not have any visible effect.
Come up with a thermometer yourself and build it. It would be especially cool if you also equipped it with a scale that would allow us to actually measure the temperature.