Force per unit area.

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2answers
85 views

Bernoulli equation as an energy conservation equation

I don’t want to learn and apply Bernoulli's equation. It is complicated and you need to remember a lot. I instead want to apply energy conservation. But I don't always find it easy. For example, when ...
0
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5answers
113 views

Pressure variation

Imagine we have a vertically orientated pressurised liquid filled closed pipe. The pipe is shaped like a spring, such that the distance between the two ends can be adjusted vertically, whilst the ...
1
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1answer
69 views

If pressure in fluids is caused by the elastic collision of fluid molecules then why does the pressure increase with depth?

We know that pressure in fluids increases with depth but why does it happen, if pressure is caused by the collision of particles?
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1answer
84 views

Intensity of sound vs Speed of sound

I am finding out the relationship between intensity of sound and speed of sound. To do that, I am using this equation: $$I =\frac{∆P^2_{\rm max}}{2ρv}$$ where ∆P max = Pressure amplitude, I = ...
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1answer
39 views

How much carbon dioxide do we actually ingest from a can of coke?

On this most trustworthy page it states that a 355 mL can of coke contains on average about 2.2 grams of carbon dioxide. As far as I know, this carbon dioxide can exist in solution as carbonic acid, ...
4
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2answers
404 views

Can pressure exist without a container?

I always hear pressure defined as the force exerted by particles on the walls of the container they're being held in. This makes sense since the mathematical definition of pressure is $ p = ...
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1answer
62 views

How is the pressure of an incompressible fluid measured?

I've googled around and can't find quite what I'm looking for.. this may be a VERY basic question, but I'd appreciate if it could be explained in layman's terms.. Traditional fuel injection engines ...
0
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1answer
42 views

How long can water hold elevated pressure and energy after opening pressure cooker lid?

I noticed today that the water warmed up in pressure cooker (1.5 ATM) dissolves sugar much faster and much more than water cooked in 1 ATM. I am interested in how long can water hold the high ...
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1answer
137 views

Questions on Pascal's Principle

I am aware that Pascal's principle says that if a pressure acts on an enclosed liquid, the pressure will be transmitted uniformly throughout the liquid. Can Pascal's Principle be applied to a ...
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0answers
172 views

Does the “luk” space suit in Seveneves make sense?

Tiny spoiler of the book Seveneves ahead. Early in the book, the Russian space agency develops an onion-like space suit called the "luk" (the Russian word for onion). It works like this: A ...
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2answers
91 views

Force due to pressure on side of box versus weight of fluid inside box

I recently solved a problem that for some reason I have no intuition about. Imagine a box of width $w$, length $l$, and height $h$ filled with a fluid of density $\rho$ on the earth (so under the ...
2
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2answers
61 views

while travelling in a bus or train, air comes inside the vehicle but it seems it goes nowhere

I have been amazed observing that while travelling in a train or bus , we feel air comming into the vehicle. I know this is due to difference in pressure but my question is that we dont feel air going ...
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1answer
37 views

Questions regarding Vacuum in space [duplicate]

The mention of vacuum has always created questions in my mind. In space isn't there near complete vacuum. If there is then why don't the oxygen travel from the suit to space (because of large ...
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1answer
34 views

measure barometric pressure using boiling water

I have set a cup of water in a bell jar, with a thermometer. I am able to lower the pressure until the water boils and I am able to measure the temperature of the water simultaneously. I then looked ...
0
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0answers
26 views

Pressure as a scalar? [duplicate]

Why do treat pressure as a scalar? We know that $P=F/A$ (Pressure = Force/Area) and force is vector quantity, so then why should pressure not be a vector?
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1answer
58 views

Putting an open can of soda into a loose plastic bag to preserve its fizz?

A friend insists that, to preserve the fizz in an open can of soda, you just put it in the refrigerator inside an unsealed plastic bag. The theory is not that the bag preserves the pressure in the ...
1
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1answer
64 views

Balancing a bowl of water

Let's say you have a mildly elliptical bowl balanced on top of a stick. This bowl is filled with water, not necessarily to the top but fairly full (I'm not 100% sure this makes a difference). You then ...
0
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1answer
62 views

Relationship between sound pressure level and amplitude of signal

I have a loudspeaker. Let's say that I feed a signal to it, say, a pure sine wave: $$f(t) = a \sin(\omega t).$$ How does the sound pressure of the resulting sound relate to the amplitude $a$? Is ...
2
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0answers
54 views

Suction from flowing water

My memory from physics says yes but I want to check. Our pool is dirty and our vacuum is broken. If I were to stick the vacuum hose into the pool drain, would the flow of water going into the drain ...
8
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3answers
2k views

Trying to understand jet engine [closed]

I'm trying to understand at a high level how a jet engine works. I want to know if the following summary I wrote is more or less accurate: The jet compresses regular air into a combustion chamber. ...
0
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1answer
55 views

Could a big enough straw stretching from Earth to space eject atmosphere into space? [duplicate]

Assuming the straw can be built out of any material, shape, size. Would the vacuum effect of space acting on the pressurized gas have enough force to lift the weight of the atmosphere contained in ...
2
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3answers
140 views

Opening tight bottles

Why do so many people recommend patting/hitting on the lid of bottles, or alternatively on the bottom, in order to open them when they are too tight? Is it even effective? And why would it work?
0
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1answer
103 views

Force on side of pool from water

Given a pool with dimensions $$\ell \times w \times h \, ,$$ I am trying to derive an equation that will yield the force by the water on the sides of the pool, namely $$\ell\times h \quad \mathrm{or} ...
3
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1answer
67 views

Perturbations on a fluid thread and hydrodynamic instability

I know that due to fluid instability there are some perturbations ( picture below ) after all of these, my question is the reason of existence of these perturbations. Why exactly they appear? Shear ...
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1answer
338 views

How can we stand up?

The atmosphere applies a large amount of pressure on us and if there is about 10 tons worth of atmospheric pressure on top of us, how can we get up from laying down?
26
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6answers
3k views

How can fast moving particles gain energy from slow moving ones?

Imagine a large diameter piston filled with water connected to a small funnel. When you press on the piston slowly but with considerable force the water will move very quickly from the funnel in form ...
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0answers
39 views

Maximum pressure in a die-less wire drawing apparatus

I ran across this patent: http://www.google.com/patents/US4549421 and was interested by the idea of reducing the cross sectional area of a wire with only shear stress caused by the wire being pulled ...
2
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1answer
62 views

Compressed air cans vs regular compressed air

I have recently learned that when spraying a can of compressed air (the ones you buy in the store) it is very cold and will freeze things especially if you hold it upside down. I know that these air ...
0
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1answer
61 views

Making sense of the Buoyancy force [duplicate]

I was reading about how to find the buoyancy force when I came across this explanation: Imagine a box submerged in a tank of liquid. The distance from the surface of the liquid to the bottom ...
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3answers
176 views

Question Regarding torricelli's theorem/Law

I recently studied about bernoulli's equation/principle. After the derivation of the said equation , my book gave some applications of the principle, which include torricelli's theorem/law. In ...
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0answers
60 views

How do I convert pressure and flow from Imperial to metric units?

I'm not a physicist or have much experience in engineering. However, for a programming task, I need to change code that calculates "pressure, head, feet of fluid, gauge" into "meters of head, ...
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2answers
54 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 ...
1
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2answers
87 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 ...
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1answer
176 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 ...
1
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1answer
89 views

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

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 ...
0
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1answer
76 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 ...
3
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0answers
61 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 ...
9
votes
2answers
262 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
35 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 ...
1
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0answers
88 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 ...
1
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1answer
1k 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?
2
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1answer
54 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
votes
3answers
98 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 ...
1
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2answers
125 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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2answers
202 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 ...
2
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1answer
208 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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3answers
927 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?
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2answers
176 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
69 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 ...
0
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1answer
96 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, ...