Air Mass


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Lesson Plan



Imagine the air around us as an ocean with the earth and its people at the bottom of that ocean of air.

Now, let's think for a minute about a real ocean. At the bottom of the sea there's enough water pressure to crush a submarine.

So, if we are at the bottom of an ocean of air why aren't we crushed by the weight of the air? Why don't we feel the air pressing against us? Maybe air has no weight at all.

Students should be asked if they think the air has no weight?
If they answer yes, ask them to provide proof for this belief.
If necessary, discuss the difference between fact and opinion.



Did you know what happens to a submarine if it tries to dive too deep? Press the button to see.



Today we'll find out if the air has weight, or mass.

We'll also find out what makes air move.

We'll answer the question, why is there wind?

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First, let's start with a simple hypothesis.

My hypothesis is that air is made out of "stuff" and stuff has weight, therefore air must have weight.

The reverse might also be true. If air has weight, it must be made of something? So, we have a two part hypothesis.

Now, we'll conduct an experiment that will either prove or disprove the hypothesis.



With the Balancing Balloons Experiment set up in advance, the instructor presents and explains the apparatus and asks the students to make some written predictions:

What will happen if the air is let out of one balloon?
Why do you think that will happen?
What will it mean if that happens?

After a few minutes of writing the instructor releases the air from one balloon and the class discusses what happens and what it means in terms of the hypothesis.

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Since we've proven that air has weight it must be made of "stuff," so let's talk about what makes up the air around us. The "Stuff" of Air.


What makes air move? What made the air come out of the balloon earlier? (Re-inflate a balloon and release the air.)

When the balloon was inflated air was forced into it under pressure. When the balloon was closed, the air was contained inside under pressure. When the balloon was opened the air rushed out because there was less air pressure outside than inside. The air expanded outward as fast as it could leaving the balloon almost empty.

So, what we're really seeing is the air moving out of a balloon because of pressure. The air moves out of the high pressure area of the balloon into the lower pressure area of the room.

When the wind blows, it certainly doesn't come out of some big balloon, but there is a similarity. Wind is simply air that is moving from an area of higher pressure into an area of lower pressure. Just like we saw happen with the balloon. Air moves because of pressure.

Discuss the following questions:
Why are there areas of high and low pressure?
What makes air pressure high or low?
What other aspect of weather is high or low?
Is the temperature the same everywhere?
Do you think there might be a relationship between air temperature and air movement?

Well, why don't we try that as the hypothesis for our experiment.

Our hypothesis will be that there is a relationship between air temperature and air movement.

We'll test the hypothesis by doing a simple experiment in small groups.


The Spiral Experiment is set up by the students in groups. Before turning on the lamp predictions are written regarding what will happen.

Students are to record what happens, speculate as to why it happens, and what it means.

Summary: Students report their results to the class and speculate what it means in terms of the original hypothesis.      

Instructor confirms or corrects the conclusions of the students.

He or she explains that warm air is less dense, or lower in pressure, because when air molecules are warmed they speed up and spread apart. This results in fewer air molecules in given area, so the air becomes lighter (has less pressure) and rises.

Cold air, which is dense (and higher in pressure) sinks and moves in to replace the rising warm air. When the cooler air moves in we experience it as a breeze or wind.

Next week we'll learn why it rains.




Lesson Plan