All About Wind for Middle School Science

Feb 21

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Wind is a part of weather and the atmosphere that we experience every day. Understanding wind means knowing how and why warm air rises and cool air falls and how the density of air causes movement.

If you would like a copy of the picture book, you can get it along with the reading passage, flashcards, and comprehension activities at Teachers Pay Teachers.

Wind

What Causes Wind?

The wind is a part of our weather, but it doesn't always blow. Some days the air around us is still, and on others, wind shakes our windows.

The wind comes from another part of the weather, air temperature. When air warms, the gas molecules that make up the air move faster and spread out. As the air expands, it becomes less dense than the air around it, so it rises.

When air cools, the gas molecules that make up the air move slower and come back together. As the air shrinks, it becomes denser than the air around it, so it sinks.

These pockets of warm and cool air exist because the sun heats the surface of the Earth unevenly. Dark-colored surfaces absorb more heat than light-colored surfaces, so the air above dark surfaces gets warmer.

Land gets hotter faster than water, so during the day, the air above land is warmer than the air above water. Land also cools more quickly than water, so at night, the air above land is cooler than the air above water.

Differences in altitude also affect air temperature. The temperature of the atmosphere is highest near sea level and decreases as elevation increases. The top of a tall mountain is cold enough to hold snow during the heat of the summer.

Air pressure describes how many gas molecules are in a given area. Low pressure means few gas molecules are present, and high pressure means many gas molecules are in the area. When warm air rises, the surface of the Earth has fewer gas molecules, so it becomes an area of low pressure.

All gases move from areas of high pressure to low pressure because gas molecules, like people, spread out as much as possible. When warm air rises, cooler air rushes in to fill the space left behind. These moving air molecules are wind.

The speed of wind depends on the pressure difference between the high-pressure area and the low-pressure area. Greater differences mean faster wind speeds.