BEAUTY OF SCIENCE / SCIENCE PHOTO LIBRARY BEAUTY OF SCIENCE / SCIENCE PHOTO LIBRARY
Thermographic footage showing the behaviour of hot water added to cooler water. Brighter areas show hotter temperatures. In the frame on the left, the hot water is dropped onto the surface of the cooler water. As hot water is less dense than cold water, it floats on the surface and there is very little mixing. This is similar to the atmospheric phenomenon called a temperature inversion, which can trap air pollution near the ground in a cold layer of air. At right, the hot water is pipetted to the bottom of the glass. In this case it quickly rises through the cold water, leading to mixing of the layers and a homogeneous temperature.
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