Heat and temperature
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10. Heat transfer. Convection

Figure 7.15
How Does Convection Occur?


The figure on the right shows how convection occurs, using hot water in a pot as an example.

When particles in one area of a fluid (in this case, the water at the bottom of the pot) gain thermal energy, they move more quickly, have more collisions, and spread farther apart.
This decreases the density of the particles, so they rise up through the fluid.

As they rise, they transfer their thermal energy to other particles of the fluid and cool off in the process.
With less energy, the particles move more slowly, have fewer collisions, and move closer together.

This increases their density, so they sink back down through the fluid.

When they reach the bottom of the fluid, the cycle repeats.

The result is a loop of moving particles called a convection current.

Cilck on the image to run a simulation showing the convection current.

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