Force per unit area.

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3answers
97 views

Pressure change with a pipe diameter change

I have a question regarding a water line from the street to a house. What happens to the pressure in a water line if it goes from a 1" diameter pipe (at street) and increases to a 1.5" diameter pipe ...
1
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3answers
4k views

Air pressure in balloon

I have to calculate the air pressure inside of an hot air balloon. After some searching I found out that I can use the ideal gas law: PV = nRT (from Wikipedia) So to get the pressure in the balloon I ...
0
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1answer
23 views

Change of temperature in liquid when it is pressurized fast to high pressure

Here's one question I've been thinking for some time: Let's assume that certain volume of water (or any other normal liquid, I'm just thinking how these kind of things should be calculated) is ...
2
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1answer
34 views

Aerodynamic noise created by cooling fan

What is the reason behind the noise created by fan blades while moving? Some paper says that it is because of the Kármán vortex street but it can be formed in static bodies only. Most of the ...
0
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1answer
181 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
1
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2answers
42 views

Can an egg be forced into a bottle by lowering the pressure inside the bottle using cold air?

I just asked a question about why ice-cold water inside a thermos results in what feels like suction on the cap. The answer stated that the cold water cools the air inside the thermos, thus slowing it ...
11
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3answers
202 views

How quickly should a fluid come to hydrostatic equilibrium?

Let's say I'm holding a one-liter water bottle, full of water, which I then drop. Before dropping the water bottle, the equilibrium is for there to be a pressure gradient in the water canceling the ...
1
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1answer
89 views

Why does very cold water in a thermos cause there to be strong suction on the cap?

After putting ice-cold water in a thermos, the cap is strongly held on by what feels like suction. I assume the cold water condenses the air, thus lowers the pressure inside, but can someone explain ...
8
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1answer
1k views

Weather forecasting with coffee bubbles

The other day I saw this life-hack: And I was wondering how true it is. First of all, I always thought(listening to weather forecasts) that low-pressure atmosphere is what correlates with rain; ...
1
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1answer
33 views

Find the separation distance for a line of oil being squashed between two flat plates [on hold]

I was wondering if someone could give me some help on how to start this problem, I'm really struggling to get my head around it. A long line of oil is being squashed between two flat plates of length ...
1
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1answer
99 views

Why does plastic wrap grow, then shrink, then grow again when microwaved?

The other night I was reheating a bowl of leftovers in the microwave. There was a fair amount of liquid in the bowl, so I covered the bowl with plastic wrap when I put it in the microwave. When I put ...
0
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1answer
26 views

Where Does the Energy Come From in this Example?

I can't figure out where the energy comes from for the work in a video I found about how the pyramids could have been made. (I do not have enough rep to post the link of it as well as the picture but ...
0
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3answers
106 views

How does pressurized gas constantly push?

If a gas, such as hydrogen, is pressurized into an air tight container, a force in terms of pascals (or whatever unit you want to use) is exerted, correct? That is what pushes against every surface ...
2
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0answers
26 views

What is the pressure of a charged gas?

I have $N$ ${\rm H}^+$ gas molecules in a sealed, electrically insulated container. What equation can I use to accurately calculate the pressure of the gas? It seems to me that $PV = nRT$ will not ...
0
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0answers
27 views

How do i calculate the amount of fluid flowing through a tube?

If I have a tube with an internal diameter of 3.5mm in inside diameter and 30cm in length with a viscosity of 1.77cp, and a pressure of 200kpa, how fast will the liquid flow through? It the tube is in ...
2
votes
2answers
396 views

Dynamic water pressure from flow and diameter

I've to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but... I don't have. After Googling a lot, I found two formulas allowing to compute the ...
1
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2answers
96 views

Pressure-Velocity relation at a point in a flow

How can we relate pressure and velocity at the same point in a fluid flow? Why does pressure decrease with increase in velocity?
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2answers
102 views

Why does Bernoulli's principle work?

So, if we have a large pipe which is constricted in the middle, the fluid in the middle section will move faster. Why is it so? What dictates that liquid that an X amount of it must pass on the other ...
3
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0answers
31 views

Superconductivity: how does the critical temperature depend on the pressure?

This question is inspired by a recent publication, in which researchers managed to boost the record critical temperature at which a substance becomes superconducting by applying an enormous pressure ...
1
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0answers
71 views

Looking for equation that explains empiric data of tire pressure change due to load

I did some measurements on how tire pressure changes due to different loads in a car. There are still some open questions I can't seem to solve on my own, even though I could already use parts of ...
13
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2answers
426 views

Definition of stress at the microscale

Take, for simplicity, a Lennard-Jones fluid below the critical temperature, which is to say that there is a phase separation into fluid and gas and thus an interface is formed. The macroscale picture ...
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0answers
13 views

wind speed and vaccume

1994 as a volunteer fire fighter we were fighting a stucture fire it was a church. the sanctuary had been built over a 1oo year old one room school building. we did not know at the time we were ...
0
votes
1answer
52 views

water fountain with a pipette

if you get some hot water in a pipette an put the pick of it on the top the water will jump out f pipette and make a fountain.I wondered if any one could tell me what is the reason?
0
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3answers
66 views

why use sparks on engines? [closed]

When the piston compresses the fuel air mixture, it heats up due to high pressure until in some point it combusts the mixture with the spark plug. What if engines dont have spark plugs, the piston ...
2
votes
3answers
142 views

Why do unused tires lose their pressure?

I have two tires, and I filled both with air at the same pressure. I used one for one month and kept the other one unused. Surprisingly, at the end of first month I found that the first tire had ...
1
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2answers
53 views

The pressure in a container of water is based on depth. So what happens if I remove the bottom of the container?

So I understand that if we have a system that involves a container of water the pressure will equal atmospheric pressure at the top and as we go further down the container the pressure will increase ...
1
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2answers
30 views

Greater pressure perceived when wearing waders

A few days ago I went for a hike in the waters of a river. I was wearing waders like the ones you see in the following picture: I don't understand why the pressure I perceived on my legs when the ...
1
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1answer
46 views

How is pressure an intensive coordinate?

Most textbooks explain intensive coordinates by asking us to consider a system and divide it into two parts. The properties which remain the same will be called intensive and the properties that ...
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2answers
35 views

Specific heat capacity at constant volume VS constant pressure

For an ideal gas, why is the specific heat capacity at constant volume lower than the specific heat capacity at constant pressure?
0
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1answer
82 views

Wanted: simple physical representation of the influence of payload onto car tires [duplicate]

From measurements I can tell that weight, as a function of tire pressure increase, is not linear but more something like this: 50kg = 1 change in pressure 100kg = more than 2 changes in pressure, ...
1
vote
2answers
106 views

Does ice melt slower in space?

If you have an ice block in the International Space Station would it melt more slowly than on Earth at the same temperature and pressure. The reason I ask is that ice can melt due to pressure. The ice ...
2
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0answers
29 views

Finger snapping: Maximum fingertip speed and generated pressure change

The wikipedia page for finger-snapping (or finger-clicking) describes the physics thus: There are three components to the snapping finger sound: (1) The "friction" or "sliding" sound between the ...
1
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3answers
995 views

A question on Bernoulli's principle

Which is more appropriate regarding Bernoulli's principle fast moving air causes low pressure or lower pressure causes fast moving air.
2
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1answer
43 views

How to compute this change of Gibbs energy for a Van der Waals gas?

The change of Gibbs energy at constant temperature and species numbers, $\Delta G$, is given by an integral $\int_{p_1}^{p_2}V\,{\mathrm d}p$. For the ideal gas law $$p\,V=n\,RT,$$ this comes down to ...
0
votes
5answers
49 views

How to increase pressure in a bottle? [closed]

Imagine a plastic bottle half full of water, what are some cheap ways to increase pressure? I'm trying to dissolve carbon dioxide in water, it doesn't happen very well at normal atmospheric pressure. ...
2
votes
4answers
43k views

Freezing point of water with respect to pressure.

I know when the pressure is reduced, the boiling point of water is reduced as well. But how does the pressure affect the freezing point of water ? In a low pressure environment is the freezing point ...
15
votes
2answers
4k views

Why is stress a tensor quantity?

Why is stress a tensor quantity? Why is pressure not a tensor? According to what I know pressure is an internal force whereas stress is external so how are both quantities not tensors? I am ...
3
votes
2answers
125 views

Expression for Atmospheric Pressure with Altitude, including Tidal Forces

Is this simple to obtain? I've tried to modify the constant-gravity model to use the $GM/r^2$ form instead, but my result was shown to be wrong with some testing. Constant Gravity Model You can ...
0
votes
0answers
45 views

What is the physical fundamentals of Pascal's law

Pascal's law or the principle of transmission of fluid-pressure (also Pascal's Principle) is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible ...
0
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1answer
26 views

Fluid pressure when it is not vertically placed

The pressure of a point in a fluid is the sum of the external pressure and $pgh$. However, when the fluid is not placed perpendicular to the ground, then what is $h$ here? For example, a cup of water ...
0
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0answers
17 views

Is lossless storage of cryo liquids practically possible due to pressure?

All cryogenic liquid storage tanks I've seen in labs are equipped with pressure relief valves, which will eventually vent all of the liquid when the tank is stored at room temperature. I am wondering ...
0
votes
2answers
28 views

What is the air pressure in a bubble of air trapped in an upturned beaker?

If I trap some air in an upturned beaker like this: What will be the air pressure inside the beaker? If I introduce say 10cm3 at atmospheric pressure via a pipe, I guess it will take up a smaller ...
0
votes
2answers
111 views

Given a slanted pipe

Question: I have a pipeline that is tilted. I know the length of the pipeline, and the pressure (90psi) that is felt at the very bottom. I'm trying to find out how much liquid has leaked out if the ...
3
votes
1answer
139 views

Is this the correct way to I combine multiple interdependant pressure readings?

I want to measure the density in different layers of a suspension. To do this I want to place pressure sensors at different heights. Let's assume that the sensors are not by orders of magnitude more ...
0
votes
1answer
34 views

How can I interpret $P(t) = \frac{1}{Q(t)} \frac{dW(t)}{dt}$ physically?

Generally speaking, one can calculate the work, $W$ (energy) required to compress a volume, $V$ of gas by integrating the pressure-volume 'loop' in a phase-space as $$W=\oint PdV$$ where $P$ is the ...
0
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0answers
37 views

Vacuum pressure equivalent in a siphon hose filled with water?

So, I was thinking about how siphons worked today, and no matter how high or low the tube goes, as long as the end is lower than the start, water will flow. So, if you took a hose, ran it up 50 ...
1
vote
0answers
34 views

On deriving a fluid flow pressure drop model using either physical theory or empirical methods

I'm trying to derive a model from physical principles of fluid flow, a simple quadratic model that tends to well fit actual pressure-flow data. For (real) subsonic air flow (ideally adiabatic) ...
26
votes
4answers
5k views

Is a bomb's shockwave strong enough to kill? [closed]

I'm watching a movie, The Hurt Locker, and the first scene shows an IED explosion which kills a soldier. Of course movies don't depict explosions with maximum realism, but I noticed the debris and ...
2
votes
1answer
160 views

How to calculate the amout of time for oil to get out from a pneumatic cylinder?

I have a system. You can assume it is just a 1" diameter steel pneumatic cylinder (1 foot long). Assume we ignore the bore size issue at this point. One chamber is filled up by oil (6" of volume), ...
1
vote
1answer
345 views

Pressure in Fluids,in particular horizontal pressure

I am not sure about the pressure existing in fluids.If the vertical pressure acts due to gravity and the atmospheric pressure since it also changes due to height also acts due to gravity then why is ...