particles. You can experience convection when you light a match. The air directly above the lit match is always hotter than the air around the match.
This difference in temperature around the match is caused by the effect of heat on the density of air. Hot air is less dense than cool air and will rise leaving the cooler air below. As the warm air rises, a pattern of air movement is formed called a convection current. We can see these convection currents in the air and in water.
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Convection currents in the atmosphere affect our weather. The rising of warm air and falling of dense cool air causes our winds. When warm, moist air rises and mixes with cold air, the atmosphere becomes unstable. This causes thunderstorms.
The Gulf Stream off the eastern coast of the States is a convection current. It carries warm water from the tropics up the east coast north toward the cold arctic waters.
Create Your Own Convection Current
Heat affects the density of water as well. You can create your own convection current with water that will allow you to see the currents caused by the density difference of water at different temperatures.
- Mix water and food coloring and pour the colored water into an ice cube tray. This experiment works best if the water is a very dark color.
- Put the ice cube tray in the freezer until frozen solid.
- Fill a clear glass with warm water.
- Add one ice cube to the glass of water.
- Observe what happens.
The warm water will melt the ice cube, but the resulting water will be very cold. This cold, dense water will sink to the bottom of the glass. You can see this happening because the melted water from the ice cube will be whatever color you made your ice cube.
As the water warms, it will rise back to the top of the glass. The colored water will allow you to see the convection current in the glass.
Try this simple experiment at home!