Why do we have air pressure inside when the roof is above us?

Question

When we are inside a room why is there the same air pressure as when we are outside. Surely the roof takes all the pressure from the gas etc above and therefore it is not on us.

Answer 1

Good question!

The thing about air pressure is that, even though (on earth) it's _caused_ by the weight of air above us, it actually _pushes_ in every direction. Up, down, left and right.

On a microscopic scale, air pressure is caused by the rapid, random motion of molecules, which continually pummel every surface they touch. It's like a bunch of machine-gun bullets firing in every direction. This creates a "push" on every surface (regardless of how the surface is oriented), and we call that air pressure.

On a MACROscopic scale, you can think of the air pressure at ground level as being caused by the weight of the overlying air on top. But the pressure still pushes equally in every direction, on every surface the air touches.

This means that the air pressure not only pushes downward on your roof, but also sideways on your doors and windows. And this means that (unless your house is 100% airtight), any difference in pressure between inside & out will quickly be equalized as air seeps into (or out of) your house through little cracks or open doors & windows.

Answer 2

I don't understand your question. Air pressure exists because air has mass. Even if there is a roof, it would have very little effect on the mass of air. Only if you change the amount of air inside as opposed to outside, then you change the air pressure.

Answer 3

firstly, i dont think questions should be met with rude replies. Questions should be welcomed, not met with hostilities.

Just remember that your house isnt airtight, there are many ways for air to get in and out, and it is a natural process that pressure equalises. That is why there is the same pressure inside as there is outside (more or less, there is probably more pressure inside). For example, if you had no air pressure inside your house, the pressure from outside, would push hard on your windows, and depending how strong they were, they would probably break, not to mention youd have no air to breathe.

Answer 4

change your name from einstein to something less absolute...

atmospheric pressure isn't supported by human structures. And if a building had a significant negative pressure, you wouldn't be able to open the door.

Human being rely on this pressure for respiration among other things. Think of the atmosphere as a liquid, like being at the bottom of a pool. You move thru it, not support it.

There is pressure on the body, (underwater you can feel it as that atmosphere is heavier) but we are designed for this pressure.

I think you don't understand the concept...