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So, what are the consequences of something

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being placed under pressure? Well, if I look

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at this balloon, I can apply pressure to it by

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exerting a force over its area. And when I do,

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well, the balloon actually gets a little bit

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smaller. The air inside the balloon gets a

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little more densely packed together. And

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in fact, this is exactly what happens on earth.

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Out here, far away from the surface of the

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earth, there are not very many air molecules.

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This is a low pressure environment and

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with nothing to weigh down on these air

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molecules from above, they’re basically

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free to play. They are free to move around.

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Now below this outer layer of the

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atmosphere, where all these air molecules

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are sort of weighing on the atoms below it,

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the molecules below it, and so these become

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a little more densely packed. And as we go

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even further down towards the surface of

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the earth, where us humans tend to live,

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the air gets even more densely packed.

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And so we see that down near the surface

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of the earth, where we have high pressure,

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we also have a high density of air molecules.

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And this high density of air molecules makes

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us humans living at the surface very happy.

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So I want to know, why do humans like high

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pressure so much? Maybe the weight from

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all that air above us keeps us from growing

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too tall. Maybe air pollution tends to go to

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regions of low pressure. Or maybe it means

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that there’s lots of oxygen for us to breathe.

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Go ahead and choose the best answer.