Force per unit area.

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4answers
4k views

Why does sound need air in order to travel?

I know that in space, because of vacuum that we can't hear voices or sound to be specific, why is that? Why does sound need a medium to go through?
5
votes
1answer
191 views

Why is the pressure on top of a slab of water greater than the pressure on the bottom?

In the image below, my book seems to be saying that if you have a cup of water in complete equilibrium, then if you have a small cube of water inside the cup given by $dm=ρAdy$ there is a downward ...
-1
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1answer
97 views

Pressure and Volume (SQA 2011 Higher Physics Q23) [closed]

On this question Part bi, the equation to be used is P₁V₁=P₂V₂, so it states that the technician removes 50ml of air from the jar, so I had: P₁=1.01x10⁵ Pa V₁=200ml P₂=? V₂=150ml (since he removes ...
1
vote
1answer
46 views

maintaining atmosperic pressure on mars

how would mankind be able to maintain an earth like atmospheric pressure on mars since mars only has 1/3rd the mass? I am not, nor have i ever attended college, but am very curious.
6
votes
1answer
200 views

Why are popcorn seeds soft after popping?

When a seed of popcorn is heated up in oil, it pops like this: You can take one of these popped pieces and eat it with little to no problem. However, if you get an un-popped seed and sink your ...
2
votes
2answers
3k views

Temperature of ideal gas after volume increases in piston

A three part question, all related Part 1. My question is about an ideal gas in a rigid container with two (equal volume) compartments separated by a rigid wall. One compartment has an ideal gas at ...
2
votes
2answers
444 views

Magdeburg Hemispheres

The Magdeburg Hemisphere experiment was the experiment that showed the effect of pressure differences on a vacuumed sphere. We know that the Force caused by pressure is $\Delta p A$ and so you can ...
1
vote
1answer
132 views

Could you blow up a barrel (closed container) using a straw and water?

Imagine you fill up a barrel with water (or any other liquid) dig a small hole at the top and place a sufficiently large straw in it, so that there is no pressure loss or anything. Then you start to ...
0
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3answers
643 views

Upward bouyant forces?

When an object is submerged in a fluid (e.g., water), there is a pressure on the object due to weight of water by p=mgh, but why is there an upward buoyant force?
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4answers
4k views

How come squeezing a water bottle makes the water come out?

This seems natural, but I can't wrap my head around it when I think about it. When I squeeze an open bottle filled with water, the water will spill out. When I squeeze a bottle, the material ...
0
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0answers
190 views

Is this how I find the rate of change of internal energy for filling a vessel?

If I am filling a tank with something (lets say air) and both its volume and pressure are changing with time (It's not rigid), it it safe for me to say: $$u=h-Pv$$ ...
5
votes
1answer
103 views

How to find the force of the compression at the core of a planet?

For example the core of the planet Jupiter, how to find out the magnitude of the force that compresses its core? and can that be thought of as the total force that holds the planet together?
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1answer
588 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 ...
2
votes
3answers
426 views

How come water in a cup won't shoot out of a straw placed inside it?

I've been learning about pressure and fluid dynamics, and I've stumbled onto a problem. Say you have a straw in a cup. The surface area of the water in the cup is much greater than that of the straw. ...
1
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0answers
71 views

If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen?

Question: If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen? Side Question: I'm imagining significantly compressed, but ...
6
votes
3answers
2k views

Why can, or can not, a perfectly incompressible fluid exist?

Water is normally assumed to be an incompressible fluid - for example in the context of calculations involving water pressure. I wondered whether that is strictly true, or an approximation? Later I ...
5
votes
3answers
341 views

Microscopic source of pressure in an incompressible fluid

The pressure of a fluid can be explained microscopically in terms of molecules bouncing off the walls of a container. The molecules have a certain mass and speed, so when they bounce they transfer a ...
4
votes
3answers
243 views

Can one pump water without providing an external source of energy? [closed]

I have a farm situated right beside a canal through which we use to get water for our crops. I am not financially sound to buy an electric motor. The water is 15ft below the ground level. So can ...
1
vote
4answers
2k views

When pressure is exerted on parallel hydraulic pistons, do they start extending at the same time?

If there are two hydraulic cylinders connected in parallel, each with a different load (shown in the picture below), will they start extending at the same time? I'm having a disagreement with my ...
5
votes
3answers
303 views

Why do tropical cyclones not tear themselves apart?

A tropical cyclone is the generic term for a hurricane, typhoon, or tropical storm. Tropical cyclones derive their energy from evaporation of water at the ocean surface which ultimately recondenses ...
3
votes
1answer
3k views

Does water turn solid under deep ocean because of high pressure?

I know that we can make water solid with high pressure, so I think water will be solid in the deep ocean? If that is true, the depth of the ocean would be limited because water will become ice? ...
0
votes
4answers
125 views

Find pressure of liquids without making contact with it

Is there any way to find the pressure of a liquid inside a closed container without making contact with it? You can make any assumptions, like transparent container or anything, only rule, the ...
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2answers
46 views

water pressure in the oceans or great lakes

Is there a way to create energy from water depth pressure? Convert the pressure to any type of energy? Does there need to be movement? Can someone comment on this process? Thanks
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1answer
138 views

Looking for the name of a physical phenomenon in fluids' mechanics

I have not even an idea about how I would search for that on Google, that is why I'm trying my chance here. As electrical engineer I have no clue about fluid mechanics. We all now that when water is ...
0
votes
1answer
45 views

Change in volume of air held at the top of a tube with upper end closed and holding some liquid [closed]

Consider a tube both end open.dip one end in a container with water..close the top with your thumb..(make sure some air remains between your thumb and the liquid in the tube)..now take the tube out of ...
5
votes
2answers
477 views

How come a whistling kettle starts whistling only when water boils, and not long before - due to hot air escaping under pressure?

A whistling kettle will start to whistle when the water boils and turns into a jet of steam which then exits the small aperture in the spout. But why doesn't this happen much earlier - when the air ...
2
votes
1answer
596 views

What is the pressure at the top of a sealed tube being drawn out of water?

Is the atmospheric pressure in a closed container the same as that of the surroundings (1 bar at sea level)? Consider a tube with both ends open with one end dipped into water (like a pipette in ...
6
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6answers
58k views

What is the difference between stress and pressure?

What is the difference between stress and pressure? Are there any intuitive examples that explain the difference between the two? How about an example of when pressure and stress are not equal?
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1answer
75 views

Do gases have a general upper limit of density?

Is there some limit for the density of gases, at which no change in condition could make it more dense without making it fluid, or solid - or something 'in between'?
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2answers
7k views

Why doesn't our body gets crushed due to the atmospheric pressure? [duplicate]

The atmospheric pressure is 101325 Pa,which is good enough to get our bones crushed.But why aren't we crushed due to it?
1
vote
1answer
136 views

Pressure at the front and back of a fan

I have a fan which is inside a duct. When the fan is off, the pressure at the front and back of the blade remains the same. Now when it is running, the velocity of the air below will be more because ...
0
votes
2answers
475 views

Can a submerged capsized vessel be turned into a sort of diving bell and propelled forward like a submarine?

I am writing a story set in the 17th century and have read accounts of such early submarines, however, not much detail is available. If some kid of weights/plummets are attached to the sides of the ...
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votes
2answers
33k views

How to calculate gauge pressure at water depth? [closed]

I am creating a program that will calculate danger at water depths for sensitive equipment and maybe humans. How do I calculate the gauge pressure at a depth $D$. Lets say $D = 5000$ meters. My ...
0
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1answer
125 views

Viability of Dysons bladeless fans? [closed]

Do Dyson's bladeless fans produce enough air pressure to cool say an air conditioning unit and do they produce a vortex pressure like a bladed fan?
0
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2answers
165 views

requirements for hydrogen fusion

What are the requirements for hydrogen atoms to go through fusion? Is it a ratio of heat to pressure or are there specific heat and pressure values that must be met (per atom or per mole?) Are there ...
5
votes
3answers
419 views

Home experiment question

I want to make a home experiment where I roughly explain the phenomenon of water remaining in a straw if you close one end of the straw. So I'm thinking that the weight of the water is pulling it ...
1
vote
0answers
29 views

Radiation pressure at high temperature

I am reading a book on the history of the hydrogen bomb. The author describes the Teller-Ulam design and explains that the liquid deuterium charge was compressed by the radiation pressure generated by ...
0
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2answers
11k views

Why do particles in high pressure air always flow to lower pressure?

The title really says it all: Why is this case? A "Feynman type" answer would be really appreciated as I'm more of a layman that a physicist.
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vote
3answers
143 views

Why doesn't water start to boil in soils?

Consider the following two scenarios: I take a vessel filled with some water and evacuate the air, the water will (or rather can) start to boil; if the pressure in the vessel is << atmospheric ...
1
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1answer
149 views

Gases at different pressures reaching uniform pressure

First of all, sorry if my question is dumb, I have very little understanding of physics. Also, English is not my native language. If two gases, initially with different pressures, are mixed in a ...
1
vote
2answers
440 views

Why does a microphone membrane only measure pressure and not particle velocity?

Microphones (e.g. condenser microphone) are assumed to have a voltage output proportional to the sound pressure at the diaphragm. If the operating principle is that the voltage output is proportional ...
7
votes
4answers
4k views

Effect of water pressure on sinking objects

As I understand, water pressure increases as we go towards bottom of the ocean. So if an object* is thrown into water and it starts sinking with some speed, does the sinking object's acceleration ...
0
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0answers
34 views

How does atmospheric pressure work? [duplicate]

I heard that yesterday the atmospheric pressure at my location was exceptionally higher than normal and that explained why I had such a terrible headache all day. But what remained unclear was... How ...
1
vote
2answers
330 views

Can an extremely small force lift a mountain in a hydraulic system? If not, then why not?

As you see in the picture, a car can be lifted with a small force F1. Here it is shown that 'F1 . A1 = F2 . A2'. What will happen if A1 is of the size of a pin's cross-sectional area. Can a child ...
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vote
0answers
41 views

Electrical resistance of a metallic conductor in a gas

A long time ago I learned that the electrical resistance of a metallic conductor, when surrounded by a gas, varies with the pressure of said gas. • What is the name (if any) of the law involved? • ...
49
votes
5answers
16k views

Why does a candle blow out when we blow on it? Our breath is 16% oxygen and only 4% CO2

Don't say that a layer of carbon dioxide covers the flame, because our breath has more oxygen than carbon dioxide. Also, our breath does not cool the flame as it is itself warm. So what is happening ...
6
votes
2answers
189 views

Why don't we include $\rho g h$ in a hydraulic jack below?

Consider a hydraulic jack with massless pistons as follows. The famous equation for this system is $$ \frac{F_1}{A_1}=\frac{F_2}{A_2} $$ My question is why isn't the equation as follows? $$ ...
0
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1answer
153 views

Airfoil theory — Why does air travel faster above? [duplicate]

I do not understand, why the air above the airfoil travels faster than the air below it? The air above has to travel faster than the air below so that both streams meet simultaneously at the ...
2
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1answer
2k views

Where is the atmospheric pressure equal to zero?

Consider the following question. My calculation is as follows. \begin{align*} P_C = P_A + \rho g h\\ P_A = P_C - \rho g h \end{align*} Because $P_C=P_0=\rho g h$ then $P_A=0$. Is it correct that ...
2
votes
3answers
771 views

How much energy needed to push a volume of water?

I am trying to solve a situation, where I'd like to know how much energy would be needed to push a mass of water out of a container. Here's an image to help understand: The water tank has a height ...