Force per unit area.
3
votes
2answers
239 views
Pressure Inside an Ideal Gas
A non-relativistic ideal gas exerts a pressure at the surface of its container
$p = \frac13 \rho \langle v^2 \rangle$
where $\rho$ is the mass density of the gas and $\langle v^2 \rangle$ is the ...
1
vote
1answer
213 views
simulations at constant pressure-volume and constant volume-temperature
I have read some papers where the authors perform simulations at constant pressure
and constant volumen or sometimes constant volume constant temperature. My question
is when is it better to use one ...
3
votes
1answer
493 views
Water under high pressure
If you were to sink a container to the bottom of a deep ocean and seal it there, then bring it up to the surface, would it retain its pressure?
The answer for a gas is obviously yes, but what about ...
2
votes
1answer
2k views
Best way to solve P-V-T Question
Typically in an exam or problem set we have a problem that's like this:
Determine the specified property at the indicated state of water. Locate the state on a sketch of the T-v and P-v diagram.
p= 3 ...
9
votes
1answer
442 views
Why does the aorta spray blood when atmospheric pressure is higher than blood pressure?
Atmospherical pressure is around 760 mmHg, while blood pressure is on average 100 mmHg. Then why do you bleed from cuts, and why does a cut aorta spray blood? The atmosphere should press the blood ...
3
votes
1answer
245 views
What kind of curve would describe the rate of air coming out of a balloon?
If one graphed the volume per time of air being expelled from a common elastic balloon out of a hole of constant size relative to the balloon's surface area, would the curve of the graph be ...
2
votes
2answers
1k views
Pressure at a given altitude?
I am trying to find out the pressure at a given altitude but have been disappointed to find the following equation does not work at all: (h = height in meters)
Where
sea level standard ...
3
votes
3answers
2k views
How does a pressure difference cause a force?
One more thing that's bothering me, could somebody clarify a little bit?
I think it has something to do with being in the state of lowest energy state, what instigates that change?
Perhaps even ...
3
votes
2answers
257 views
$P$ = $ρgh$ - intuitive understanding of the equation?
I've come across this equation recently which relates pressure with the product of density, gravitational acceleration and height difference in a medium.
I understand that
$P$ = $ρgh$ expands to ...
2
votes
7answers
3k views
Why does the gas get cold when I spray it?
When you spray gas from a compressed spray, the gas gets very cold, even though, the compressed spray is in the room temperature.
I think, when it goes from high pressure to lower one, it gets cold, ...
0
votes
1answer
882 views
What are the differences between the terms flammable, inflammable, and non-flammable? [closed]
This question should perhaps go in Chemistry, to which I am committed, but since the Chemistry Stack Exchange forum is not yet in beta, I am wondering if you can help me from a physics perspective.
...
0
votes
1answer
161 views
determine temperature at which pita bread will expand in a toaster
suppose you have a pita pocket of radius 5cm or .05m. We will model the pita pocket as consisting of disk with a layer of air of volume V which is contained by the surface of the bread. We will ...
0
votes
1answer
173 views
what is the relationship of sound volume to atmospheric pressure?
what is the relationship of sound volume to atmospheric pressure? if I was in a plane with a cabin pressure equal to 8000 feet would the volume drop be noticable?
4
votes
2answers
249 views
How to calculate the highest theoretical artificial hill?
The biggest peak in the world is Mount Everest.
Imagine someone starting to make an artificial hill (like pyramide) from soil (earth).
So, when starting with an 200x200 Km base area, with 45degree ...
5
votes
1answer
122 views
question about a fly
suppose there is a scale able to measure weight with an uncertainty of $10^{-9}kg$ . On the scale, an airtight plastic chamber is placed. Initially, a fly of mass $10^{-5}kg$ is sitting at the bottom ...
0
votes
3answers
134 views
What is the volume of a parcel of air of a giving weight at average sea level pressure
I know this is probably some basic math once you have the figures, but my Google-fu is failing me.
Say I have 5 pounds of air. Air meaning, the typical composition of the atmosphere of Earth. And by ...
5
votes
3answers
480 views
Get an intuition for pressure values
I am currently working with pressure differences in the milibar range. However I do not have a good feeling for pressure differences. In every day life:
Where does a pressure of say 100 mbar over ...
1
vote
1answer
135 views
Non-Dimentionalization of equations
I am trying to understand a paper in which they mention;
" We non-dimentionalize the problem hereafter by selecting mass, length and time units such that the fluid density
$\rho\equiv1$
the ...
4
votes
0answers
777 views
Inflating a balloon (expansion resistance)
I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
1
vote
1answer
129 views
Is acoustic pressure a statistical term?
Is acoustic pressure a statistical term? Also, what about pressure in a liquid or a gas?
5
votes
1answer
1k views
Why do some carbonated drinks fizz more than others?
Wired magazine ran an article this month on carbonation in soft drinks.
If all soft drinks are manufactured effectively identically, why do some types fizz more than others?
For example, root beer ...
1
vote
1answer
149 views
In a low pressure (near vacuum), -20°C vessel, would sublimated moisture rise to the top or fall to the bottom?
If I have a strong vessel that I've cooled to say -20°C, and lowered the pressure below 0.006 atmospheres, the water in food placed inside will sublimate and freeze dry the food.
But what happens to ...
1
vote
3answers
567 views
Maxiumum weight a buoy can float [closed]
I have a buoy that can hold 2943.02 cubic millimeters of non-pressurized air, I need and equation to work out the maximum weight that the buoy can float.
3
votes
2answers
1k views
How deep in the ocean can a ping-pong ball go before it collapses due to pressure?
Stimulated by the calculation showing that a ping-pong ball does not pop in vacuum, I'm driven to ask how deep in the ocean a ping-pong ball can be brought before it collapses due to pressure.
This ...
4
votes
2answers
712 views
If I put a ping pong ball in a vacuum, would it pop?
If I put a ping pong ball in a vacuum, would it pop? If so, at what point would it happen? Any standard table ping pong ball is acceptable.
0
votes
2answers
1k views
If you put a latex balloon in a vacuum, how much would it expand?
If you put a latex balloon in a vacuum, how much would it expand? And would it pop? Assume it doesn't leak.
EDIT:
Some numbers: Ambient pressure is 100 KPa, balloon is perfectly spherical with a ...
2
votes
3answers
189 views
Making a “heavier-than-air” craft float
How big would a hollow rigid object need to be to float, (not in water but in air) if all of the air was vacuumed out and the container sealed?
6
votes
1answer
364 views
What is highest water pressure at which electrolysis can be performed?
What is highest water pressure at which electrolysis can be performed to derive hydrogen and oxygen? Does the dielectric constant of water, which which lowers as pressure increases, have an effect on ...
11
votes
2answers
436 views
How to model/simulate pressures and flows in a network of pipes
I'm having a hard time finding information on how to model/simulate this. I attached a couple files, both of which show an example tank & pump network. It's just nonsense that I made up for this ...
5
votes
1answer
3k views
How is formula for converting pressure from mmHg to Pa derived?
Today my younger brother asked me from where does the 1 Pa = 0.00750061683 mmHg formula for mercury barometer come. He needs a way to derive it, or an academic source which can be cited.
After ...
3
votes
2answers
284 views
Alcohol inside a container
Let's imagine a plastic container completely closed. We put alcohol inside it filling it at half. Now we make a hole to introduce 2 little Conductor one near the other so that they don't let the air ...
1
vote
2answers
674 views
Tube under water and air pressure
If you take apart a syringe you are left with one piece that is a tube with a tiny hole in one end and the open end of a tube at the other. If you then submerge this underwater and cover the small ...
2
votes
3answers
3k views
Explanation for different boiling points of water on different altitudes
I understand water boils at different temperatures depending on altitude.
I am seeking to get an illustrative explanation for this, including a diagram if possible.
1
vote
3answers
403 views
Why isn't pressure a measure of energy?
Hey guys, I'm having a problem in understanding the 1st Law of Thermodynamics.
If i would increase the pressure of a closed system by compressing a gas in a cylinder isothermal, the 1.Law states, ...
3
votes
5answers
308 views
Aside from carbon, what materials change structure under intense pressure?
I was thinking the other day about what sort of exotic materials one would find in the depths of a planet. I have heard theories about how an enormous diamond might be found in the centre of gas ...
8
votes
4answers
1k views
Water pressure in free fall
The increasing water pressure as you go deeper is generally explained in terms of the weight of the water column above the observation point pressing down. The question, then, is what would happen if ...
3
votes
4answers
5k views
Why will crushing a partially empty 2-liter bottle keep the soda more fizzy?
One of the curses of 2-liter bottles is that when carbonated beverages are stored in them for long periods (i.e. days between drinks) at least the last liter ends up being flat. However, if after ...
5
votes
5answers
633 views
What would ACTUALLY happen to a person jettisoned into space?
[insert obligatory statement of my lack of knowledge in physics]
Alright, so we have all seen the movies where someone gets blasted out of the airlock on their starship, or their suit decompresses ...
5
votes
3answers
517 views
Why is Avogadro's hypothesis true?
Why is the number of molecules in a standard volume of gas at a standard temperature and pressure a constant, regardless of the molecule's composition or weight?
Let's say I have a closed box full of ...
5
votes
3answers
258 views
Will an air-filled tire normally gravitate toward being nitrogen-filled just by refilling with air?
A big argument by the nitrogen-in-the-tire crowd is that:
Nitrogen atoms are bigger and thus less likely to escape the tire, bringing stability to your tire pressure.
If Earth's atmosphere is ...
36
votes
11answers
4k views
How long a straw could Superman use?
To suck water through a straw, you create a partial vacuum in your lungs. Water rises through the straw until the pressure in the straw at the water level equals atmospheric pressure. This ...
2
votes
2answers
1k views
Balloons and lifting gases
Hydrogen is the lightest element, so it's cable of lifting the most weight in out atmosphere (probably not the best terminology there, but you get the picture)
Would hot hydrogen (in the same sense ...
9
votes
4answers
2k views
Why can't CO2 mix back with the liquid after a soda bottle has been shaken?
If you shake a soda bottle before opening it, and then open it, you get the fizz.
That is the compressed CO2 releasing to the atmosphere which is at comparatively low pressure value.
Two questions ...
10
votes
4answers
956 views
How does a steady wind flow generate sound?
When a wind blow through sharp edge, say, edge of a paper, you can see the vibration of the paper and hear the sound.
For this type of oscillation, it should be a damped oscillation with external ...
0
votes
2answers
407 views
Would weighing scales show a negative weight if placed in a vacuum?
The weighing scales in my kitchen are currently showing 0 Kg. However, there is a column of air between the scales and the ceiling that is presumably exerting pressure on them. If I were to place ...
6
votes
3answers
2k views
Why does the water level equalize in a series of tubes?
Say I have a series of tubes (not the internet) looking like this, where w represents water:
...
3
votes
3answers
1k views
What is the relation of sound propagation to air pressure?
Hi there i am wondering, air is making sound propagate. So in vacuum there is no sound. but what is the relation of pressure to sound volume? is it linear?
if i have a source of sound and lets say i ...
18
votes
4answers
1k views
Why can you “suck in” cooked spaghetti?
We all know that there is no "sucking", only pushing. So how are cooked spaghetti pushed into your mouth? The air pressure applies orthogonal on the spaghetti surface. Where does the component ...
