# Atmospheric Pressure: Definition & Effects

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• 0:00 Definition
• 1:17 Altitude
• 1:58 Temperature
• 2:37 Lesson Summary

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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

Atmospheric pressure is around us all of the time. The air you are breathing has weight, and although it doesn't weigh a lot, there is a lot of it around. This lesson will cover atmospheric pressure and its effects.

## Definition

It can be odd to think of air as having weight - after all it doesn't feel like it! But the air is full of molecules and though extremely light, they do have weight. The more air you have above a thing, the more weight that thing will feel.

Atmospheric pressure is the weight of the atmosphere on a surface. The units for atmospheric pressure are conveniently known as atmospheres (atm) and the average pressure at sea level is set at 1 atmosphere (atm).

On average, the weight of the atmosphere on a square inch is 14.7 pounds at sea level. This means if you were to extended a 1-inch column from sea level to the edge of our atmosphere, all the gases inside would weigh 14.7 pounds. Another way to think about it is, if you put your hand out, there is more or less 175 pounds of atmosphere weighing down on it, and a standard 8.5 x 11 piece of paper has over 1300 pounds weighing down on it.

So why doesn't it crush us? Luckily we have evolved to deal with it and not notice it. In fact, we would have big problems if there wasn't all that pressure keeping us together.

## Altitude

The atmospheric pressure at any given point depends on two factors:

• Altitude - the height of a thing in relation to sea level
• Temperature - the intensity of heat

As you increase altitude, the amount of atmosphere above you decreases. In other words, if you start to climb a mountain, you will gradually have fewer and fewer gas molecules above you. This will mean there is less atmospheric pressure being exerted on you every step of the way. In fact, at about 3 miles up the atmospheric pressure is only half of what it is at sea level! If you can make it up to 20 miles, there is essentially no atmospheric pressure (and you would most certainly die, but that's beside the point).

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