Fremont Magnet Elementary

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Wind, Where Does It Come From?

Standard 4a: Students know uneven heating of Earth causes air movements (convection currents)

 1. Review of Earth's Atmospheric Pressure

Last week you learned about Earth's atmosphere and pressure

Which of these is true?

  Air pressure pushes more on the side than on the top.
  Air pressure pushes more on the top than on the side of your body.
  Air pressure pushes against your body equally from all directions.

 

The higher up in the atmosphere you go, the air pressure ____
 

  increases (more)
  decreases (less)

 

2. What is a current?

You learned that we live at the bottom of a 'sea of air'.  Just like water in a river, the air around us moves.  This movement is called a current.  A current is a flow of water, air, or gas.

 

3. What causes the current of air to move? 

 

The heat that comes from the Sun shining on the Earth.

4. How does that work?

The Sun heats the Earth's surface. 

The air that is near the surface begins to get warmer.  As the air gets warmer, the air molecules move further away from each other. 

Warm Air Molecules are spread apart.
They are less dense and light		 Cold Air Molecules are close together
They are more dense and heavier.

Click here to experiment with temperature changes and air molecules

 

This means the warm air is less dense or lighter, so it floats up.

The higher it goes the colder it gets, and the air begins to cool off.  As it cools off, it begins to sink back down again because it is denser, or heavier.   The air in our atmosphere is constantly moving.  This cycle of air molecules moving up and down is what causes wind.

5. What is a convection current?

You know that it is warmer at the Equator than at the poles because Earth is tilted, so the Sun shines more at the center or the Earth (Equator) than at the top and bottom (Poles.  The warmer, lighter air at the Equator moves toward the cooler air at the poles. The cold heavy air at the poles moves toward the Equator.  This causes a constant 'river' of air movement called convection currents.

This picture shows the flow of convection currents.  They go around, and around, and around, constantly moving the air in our atmosphere.

6. Why are some days windy and some days not windy?

When two convection currents meet, it causes the wind to blow.  Think of two streams of water that come together.  The water bubbles and splashes more where the two streams meet.  Streams of air, convection currents, are similar.

Discover why some days are windier than others by using the weather machine.

Experiment with the different temperatures.  What do you notice about the wind?  How do you make a strong wind? 

7. Summarize

To see a summery of how weather works, click on the picture below and choose PLAY THE MOVIE.

 

 

Draw a picture or write about what you have learned.

 

 

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