Force per unit area.
38
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 ...
18
votes
4answers
2k 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 ...
13
votes
3answers
354 views
Why don't I feel pressure on my body when swimming under water?
If I put a couple of lead bricks on my foot, there would be a definite sensation of a heavy, perhaps even painful, force. Calculating the pressure for $20 kg$ of lead over a $100 cm^2$ area of my ...
11
votes
2answers
449 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 ...
10
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
971 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 ...
9
votes
1answer
462 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 ...
8
votes
5answers
2k views
If I take a bottle of air into space, and open it, where does it go?
It seems to me that space doesn't have any/much air, and if my bottle is full of air, when I open it, where does the air go?
8
votes
1answer
567 views
Why doesn't a bus blow due to internal pressure?
When one travels in a bus, if he's sitting at any window, he will feel that the air is coming inside. If someone is standing at the open door of the bus, he'll also feel that the air is coming ...
8
votes
4answers
2k 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 ...
7
votes
2answers
325 views
At the molecular level, how is the pressure at the bottom of a lake higher than at the top?
Surely the temperature of the molecules is the same throughout the water. Using $p = \rho g h$ seems to assume a constant density as well. But then how is it that the force per unit area on an object ...
7
votes
2answers
159 views
Why water in the sink follow a curved path?
When you fill the sink with water and then allow the water to be drained, the water forms a vortex.. And then it starts to follow a curved path downwards by effects of gravity..
Why this phenomena ...
7
votes
4answers
453 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 ...
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:
...
6
votes
3answers
154 views
What about negative Pressure?
Here is something I see :
Let's say the ideal fluid(water here) of density $\rho$ is drawn from a source by a motor and thrown upwards with a velocity $v$. Now we take the power of motor be ...
6
votes
2answers
157 views
Hydrostatic pressure on a teapot spout
The phenomenon where water flows on the outside side of a teapot spout is named "The teapot effect", and occurs due to a difference in pressure between water and the atmosphere. Consider the image of ...
6
votes
1answer
154 views
What is the cause of noise generation at my bike helmet
I am looking for anexplanation of this phenomenon:
I was riding my bike, (not driving it, was sitting on the back seat) with the helmet on. While the glass of the helmet was intact, I could hear ...
6
votes
1answer
480 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 ...
6
votes
1answer
375 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 ...
6
votes
2answers
194 views
At what velocity does sea water leave a pipe run into a fresh water lake (for equal surface levels)?
If I took a fresh water lake* whose surface is exactly as sea level, and connect it to the sea with a pipe filled with sea water, with both ends of the pipe at exactly the same depth from the surface, ...
5
votes
3answers
571 views
refrigerator door resists 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?
5
votes
3answers
510 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 ...
5
votes
3answers
522 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
263 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 ...
5
votes
5answers
653 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
1answer
225 views
Water flushed down, water pumped up (in buildings)
I live in a tall building (20 floors) on a mountain. Because the water pressure from the water company is not enough, there is a water pump at the last floor which is activated each time someone is ...
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 ...
5
votes
3answers
103 views
Atmospheric pressure experiment using a cup with a fluid to hold a glass plate
When I was in high school, my teacher did an experiment to show the power of atmospheric pressure.
Experiment:
Prepare a glass bottle, fill with water, put a glass plate on the bottle, make sure ...
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 ...
5
votes
1answer
371 views
Why is pressure in a liquid the same in all directions?
I'd like answers both in the more intuitive side an on the more precise side.
Thinking of water as "cubes" of water, for example, would allow pressure in the z axis to be independent of the y or x ...
5
votes
2answers
205 views
Keeping air in a giant gravitationally-bound space balloon
Let's say a space-faring society wants to make a space station that has a large volume filled with air (or other gas), but no gravity. Using normal pressure tanks will require gathering an amount of ...
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 ...
5
votes
1answer
87 views
What if the lid of a pressure cooker was suddenly released?
My dad and I have tried to calculate the strength of the explosion if the lid was suddenly freed. We took some measures:
Lid mass: $0.7 \textrm{kg}$
Lid surface: $0.415 \textrm{m}^2$
Internal ...
4
votes
3answers
127 views
Is it easier to pump water up or down?
I'm trying to gauge the strength of aquarium air pumps, for use in a vertical hydroponic farm. A curious question arose: is it easier to pump water upwards vertically, or is it easier to pump it ...
4
votes
2answers
162 views
What's the classical limit of the pressure of the ultrarelativistic Bose gas
The pressure for the ultrarelativistic Bose gas is
$$p~=~U/(3V) ~\propto~ (kT)^4/(hc)^3.$$
It looks to me like it diverges for $h \to 0$. Looking at the derivation, it diverges because $h$ is the ...
4
votes
2answers
719 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.
4
votes
3answers
203 views
How can I keep a smaller water reservoir's water level at half available when being fed from a larger reservoir? [closed]
I'm trying to create my own ultrasonic humidifier. I ordered the misting part which works great but it only functions correctly in shallow water. So I'd like to feed from a large water reservoir to a ...
4
votes
1answer
131 views
Flow of momentum is pressure
In the diagonal terms of the energy-momentum tensor, the flow of $x$-momentum in the $x$-direction is the $x$-pressure. Why the flow of momentum is pressure?
4
votes
2answers
255 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 ...
4
votes
2answers
1k views
Why does the balloon pop?
When we pierce a balloon with a sharp needle, it pops and produce a great sound. But, It doesn't pop when we open the mouth of the balloon (through which we have blown air)...
So, Why doesn't the gas ...
4
votes
1answer
262 views
What is the meaning of pressure of a solid?
Currently I'm taking an introductory course on thermodynamics. I've got a problem with understanding what is the meaning of pressure of a solid body. The question arose when I looked at phase diagram ...
4
votes
1answer
49 views
What is the minimum pressure difference for your ears to pop?
I'm assuming the answer to this largely varies from person to person. Assuming you could instantly change the pressure around your head by amount $\Delta p$, what is the minimum $\Delta p$ for your ...
4
votes
2answers
141 views
Physics behind the flow of gas coming out of a balloon
I'm working with stratospheric balloons (latex ones) and I want to put a valve on it so it can float for a longer time. I'm trying to define which valve I should use, which demands I estimate the flow ...
4
votes
3answers
131 views
Effect variable cylinder radius has on airflow
Can someone shed some light on the following problem? I'm unable to get any traction on it as I know nothing about fluid dynamics (I'm a computer engineer).
It's a problem I made up over a lunch ...
4
votes
1answer
173 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 ...
4
votes
0answers
784 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) ...
3
votes
5answers
309 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 ...
3
votes
3answers
741 views
Define Pressure at A point. Why is it a Scalar?
I have a final exam tomorrow for fluid mechanics and I was just looking over the practice exam questions. They do not provide solutions. But pretty much I have to define pressure at a point and also ...
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 ...
3
votes
1answer
95 views
Why doesn't soda fizz at high pressure?
In this video, a can of soda is opened in an underwater station at 2.5 atm. The demonstration is that shaking the soda doesn't cause it to explode like it would at normal pressures.
Why does this ...
