Force per unit area.

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7
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4answers
1k views

What is the meaning of pressure of a gas

I understand the meaning of pressure on a surface to be force acting per unit area. But when it comes to understanding pressure in the context of fluids in motion or at rest I think I am having some ...
-1
votes
2answers
240 views

Fuel Tank Question

Could some one please help me with this question as my physics knowledge does not extend this far. I have a large fuel tank with a capacity of 21000L. The tank currently is holding 2000L of fuel. On ...
1
vote
0answers
86 views

What is approximately critical Q for the space shuttle? [closed]

Everything is in the title, I wonder what was approximately the critical dynamic pressure the space shuttle (RIP) could handle, as I am trying to create a simple space flight simulator. I don't need a ...
8
votes
1answer
945 views

Ping-pong ball pontoon

Imagine a vertical pipe (both ends opened) in the water. Drop several ping-pong balls into pipe and cover them with a cylinder. When you have enough balls, the cylinder will float. Now start adding ...
14
votes
5answers
4k views

Why does my refrigerator door resist opening?

After closing my refrigerator's door I noticed that it's much harder to reopen it immediately, as if there's an underpressure. Only after a minute or so it opens normally. How can this be explained?
4
votes
1answer
205 views

Can i use coils with compressed air to make a superconductor?

What im saying is inside pipes i am going to use compressing so that that in the places with low pressure they cool the superconducotor. is this possible? Can i use this concept to make ...
3
votes
2answers
342 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
2answers
391 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 ...
6
votes
2answers
1k 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
7k 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 ...
10
votes
1answer
2k 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
501 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
5k 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
4answers
6k 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
4answers
422 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 ...
8
votes
8answers
18k 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
2k 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
199 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
294 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
396 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 ...
0
votes
3answers
248 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
857 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
156 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
1k 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
133 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
3k 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
177 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
2k 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.
4
votes
2answers
3k 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
1k 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
3k 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
212 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
671 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
1k 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
12k 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
411 views

Burning alcohol vapor

Let's imagine a plastic container, sealed closed. We fill half of it with alcohol, then we generate a spark. The question is: can the mixture of alcohol and air burn, or do we need a hole to let air ...
1
vote
2answers
995 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 ...
3
votes
3answers
19k 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
815 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
398 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
3k 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 ...
10
votes
5answers
11k 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 ...
7
votes
4answers
1k 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
795 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
364 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 ...
47
votes
12answers
10k 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
4answers
2k 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 ...
13
votes
4answers
5k views

Why can't CO$_2$ 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 ...
11
votes
4answers
2k 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
784 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 ...