How does atmospheric pressure work?

In summary, the pressure of a gas is due to the collisions of its molecules against a surface. Atmospheric pressure is measured by taking the weight of all the air molecules above a surface, including the ones that aren't contacting it. This is because the air pressure is what prevents the entire atmosphere from collapsing onto the ground. There is no obvious piston to picture air pressure, but it can be visualized using a container and piece of paper. This concept is used to build a barometer.
  • #1
yunocell
3
0
From what I know, the pressure of a gas is due to the collisions of its molecules against a surface. So I don't understand why atmospheric pressure is measured by taking the weight of all the air molecules above a surface including the ones that aren't contacting it. Gases have plenty of space between their molecules so I don't understand how I can feel the weight of a gas molecule one mile above me that isn't in contact with anything else. Can somebody please enlighten me? Thanks in advance.
 
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  • #2
Welcome to PF;
The gas in the air all bumps into each other so how hard the molecules close to you bump into you depends also on how hard all the other molecules bump into each other. So it is reasonable to expect that the air way above you would have some effect.

The reason this effect comes to the weight of the air above a spot on the ground is that the air pressure is what stops all the air being a thin pancake under your feet. There has to be enough pressure to hold the whole atmosphere up.
 
  • #3
Ok, I think I understand now. Thanks for the answer!
 
  • #4
If you has a cylinder of air with a piston on top that was being held up by the pressure in the container, then you'd have to figure the pressure in the container in terms of how heavy the piston was right?
It works like that with water pressure too.

The trouble with picturing air pressure it there is no obvious piston ;)

But you should have a decent mind-pic now to go on with.
 
  • #5
So if I go outside and I get a container and a piece of paper, and I put the piece of paper on top of the container to seal it, does that mean that the inside of the container is 14.7psi (atmospheric pressure) just like the outside?
 
  • #6
yunocell said:
So if I go outside and I get a container and a piece of paper, and I put the piece of paper on top of the container to seal it, does that mean that the inside of the container is 14.7psi (atmospheric pressure) just like the outside?

Yes.
 
  • #7
... if there were a difference, then the paper would bend.
This effect can be used to build a barometer.
 

1. What is atmospheric pressure?

Atmospheric pressure is the force per unit area exerted by the weight of the Earth's atmosphere above a certain point on the Earth's surface.

2. What causes atmospheric pressure?

Atmospheric pressure is caused by the weight of air molecules in the Earth's atmosphere being pulled down towards the Earth's surface by gravity.

3. How does atmospheric pressure affect the weather?

Changes in atmospheric pressure can affect weather patterns by influencing the movement of air masses and the formation of weather systems. High pressure typically brings clear, dry weather while low pressure is associated with cloudy, stormy weather.

4. How is atmospheric pressure measured?

Atmospheric pressure is commonly measured using a barometer, which measures the force exerted by the column of mercury in a tube due to the weight of the air above it. The unit of measurement for atmospheric pressure is typically in millibars or inches of mercury.

5. How does altitude affect atmospheric pressure?

As altitude increases, atmospheric pressure decreases because there is less air above pushing down. This is why it is more difficult to breathe at high altitudes, as there is less oxygen in the air due to the lower atmospheric pressure.

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