# Atmospheric pressure

1. Dec 3, 2015

### huyhohoang

Hello everyone!
As we've known, the pressure at the bottom of a volume of gas is define by its weight times the height. So I wonder why the atmospheric pressure is equal in all direction?
Many thanks

2. Dec 3, 2015

### Staff: Mentor

Hi.
I don't understand what makes you think one thing has something to do with the other.

3. Dec 4, 2015

### Staff: Mentor

When we say that the "pressure is equal in all directions," what we mean is that, at a given fixed location, no matter which way you orient a surface upon which the pressure is acting, you get the same value for the pressure. So, we are not referring to changes in pressure with spatial location.

4. Dec 4, 2015

### nasu

This is not true. Weight times height doesn't even have the right units to be a pressure.

5. Dec 4, 2015

### Staff: Mentor

I think the statement about it being "the bottom of a volume" implies the OP correctly understands it's over the surface area at the bottom of the column.

6. Dec 4, 2015

### jbriggs444

But the result would still be wrong. Weight times height does not have units of force.
Density times height -- now that would have units of pressure -- at least if you measured density in force units.

7. Dec 4, 2015

### Staff: Mentor

Yeah - he shouldn't have said height at all since he already has the weight. Still is only tangential to the question he's asking, so probably not worth the extra few posts discussing it.