Does air pressure increase or decrease as you move higher into the atmosphere? Why?

Answer 1

It decreases, but not because of gravity. In fact, even at the upper edges of the atmosphere, the gravity is hardly any different to how it is on the surface. The pressure decreases because there is less air above you. Imagine a "sea" of air sitting on top of you all the time. That's what is responsible for the 101.3 kPa of pressure you feel. As you increase your altitude, just like if you were coming up from deep under the water, there will be less fluid on top of you pushing down, thus the pressure will decrease.

Answer 2

The phenomenon is called "hydrostatic equilibrium". If you imagine a small volume of air, it has some weight associated with it. Weight means it experiences a net force downwards due to gravity. If it is not moving, that means there must be a net force exerted on it that is slightly larger from below than from gravity and the force above the volume from its pressure. The pressure from below it MUST therefore be higher than the pressure from above.

Now if you turn the volume into something infintesimally thick you get a simple differential equation. (simple if you have had calculus and some Diff Eq. study, which really is not as scary as it might sound to some people).

When you solve it, you find that the pressure decreases exponentially(*) with altitude as long as you assume there is no motion in the fluid/gas in question.

Hydrostatic equilibrium applies to any fluid system. In a compressible fluid (like a gas) the only change is the relationship between density and pressure is not so simple. Temperature plays a role in the density, so you have to know the temperature as a function of height AND the altitude to predict the pressure.

Yes, eventually gravity will change enough with altitude to make a difference but when you realize that the air is already 1/1000 surface density around 55km, it is going to be REALLY thin by the time changing gravity makes a difference.

(*) Exponential here means that for a given distance, the pressure falls off a certain percentage. For the earth and the molar density of air, this means the pressure falls off by half for every 18,000 feet (3.5 miles; 5.5 km). Yeah, it never quite reaches zero. A scientist would say the the "Pressure scale height" of the atmosphere is 9 km assuming 27 deg C air all the way up. This means that every nine km, the pressure drops by a factor of 1/e (e ~ 2.7).

You can learn more detail about hydrostatic equilbrium at http://en.wikipedia.org/wiki/Hydrostatic_equilibrium

Answer 3

You have a few correct and partially correct answers here. It is true that air pressure decreases as you go higher in altitude. This is because the weight of the air above you is less. But why is that so? Well because of gravity. The Earth's atmosphere has a limit. It doesn't extend forever out into space. The limits of the atmosphere (ie its total size) is determined by two main factors: the gravitational force exerted by the Earth and the temperature of the atmosphere. Temperature is just a measure of how fast the molecules in a gas are bouncing around. The higher the speed of the molecules, the higer the temp. At some point, the molecules in the gas have enough speed to escape a the Earth's gravitational field (just like a rocket going to another planet). The balance between temperature and gravitational pull determine the total "height" of the atmosphere. And thus determine how much mass is above you at any given altitude. Density of the gas is also reduced by the increased volume that exists at high altitudes. If you put a certain mass of air into a ring around the Earth at sea level and then same mass of gas into a ring at 100,000 feet and keep the temperatures the same, the density in the ring at sea level will be much higher because the ring has a much smaller volume.

Answer 4

Air Pressure Decreases As

Answer 5

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RE:
Does air pressure increase or decrease as you move higher into the atmosphere? Why?

Answer 6

Air pressure is the force exerted on you by the weight of tiny particles of air. Although air molecules are invisible, they still have weight and take up space.

Air at sea level is what we're used to, in fact, we're so used to it that we forget we're actually feeling air pressure all the time.

If you've ever been to the top of a tall mountain, you may have noticed that your ears pop and you need to breathe more often than when you're at sea level. As the number of molecules of air around you decreases, the air pressure decreases. This causes your ears to pop in order to balance the pressure between the outside and inside of your ear. Since you are breathing fewer molecules of oxygen, you need to breathe faster to bring the few molecules there are into your lungs to make up for the deficit.

As you climb higher, air temperature decreases. Typically, air temperatures decrease about 3.6° F per 1,000 feet of elevation.

Answer 7

Air pressure decreases as you go up. Why? There is less air above you at higher altitudes. Air pressure is caused by the weight of the air above you pushing down on you. Less air means less weight, which means less pressure.

Answer 8

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Answer 9

Air presuure decreases as the height increses, because density of air decreases with the increase of height, which results in decreasing of weight per unit of area.

Answer 10

It decreases. The Earth's gravity attracts the air molecules, causing more of them to be nearer the Earth's surface. (More molecules = higher density near the ground)

It's not due to gravity decreasing as you get higher in altitude, it's simply due to the existence of gravity.