Force per unit area.

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2answers
47 views

Negative pressure

How is negative pressure created in a fluid system?Isn't it counter intuitive that we are reducing the pressure of a system containing no molecules(zero pressure) to a lower value?
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4answers
79 views

Can this container withstand a vacuum? [closed]

I am putting together a piece of equipment that will involve a vacuum pump pulling up to 10 Torr / 13 Mbar.  I need to use a container for liquid within the equipment and have found a stainless steel ...
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2answers
52 views

Would an airtight box filled with air act the same way to 1 bar of water pressure as the same box vacuum-sealed at atmospheric pressure?

Pressure On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N (2.28 lbf) ...
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1answer
63 views

How to convert cc to bar?

In astronomy/astrophysics, medium density is often given in cc, particles per cubic centimeter. Also, the temperature of the medium is usually given, in Kelvins. For some materials the melting point ...
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2answers
195 views

Calculating pressure under water

Say I were calculating the pressure under 1 foot of water, in psi. I'm thinking the pressure is force per unit area, and should be equal to the force exerted by the column of water standing over ...
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1answer
5k views

Calculation of pressure from flow rate of water

Anybody kindly help me to find how to calculate pressure in bar from flow rate. I have a pipe and from that I am transferring water at a constant flow rate of 5ml/min. At this flow rate, with a 0.5 cm ...
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2answers
198 views

Pressure $p$ in the Bernoulli equation

I know the Bernoulli equation that states that the energy along a streamline is constant: $$ \frac{v^{2}}{2}+gh+\frac{p}{\rho}=C $$ However I can't seem to figure out what exactly $p$ is in this ...
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2answers
789 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 ...
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4answers
93 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
4k 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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1answer
98 views

Conclusions From a Junior School Science Experiment

If you stick a tissue to the bottom of a glass and immerse this glass fully (upside down) into a tumbler of water, then this tissue remains dry. Why is this so? / What conclusion would you draw from ...
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117 views

Simulate free fall in a rotating torus?

Say I have a rotating torus filled with air at 1 atmospheric pressure at sufficient speed (and inclined along the direction of the force of gravity with respect to Earth). If the rotation speed were ...
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1answer
98 views

What is responsible for cutting an apple: pressure or force?

To cut an apple, do I need more pressure or more force? When we want to destroy the intermolecular bonds, don't we need more force ?
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1answer
159 views

Does the space between molecules have no pressure?

In any living organism there exists are space between cells filled with interstitial fluid. Loss of this fluid into abnormal areas (3rd spacing) can cause relative to severe hypo-volemia. The fluid ...
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2answers
592 views

effect of atmospheric pressure on reading of a weighing scale

Let us consider a completely sealed weighing scale such that the air pressure above and below the pan of the scale are equal and is equal to 1 atm. pressure. The scale initially reads zero. Now if ...
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1answer
76 views

How does a small radius connector affect gas flow?

Assume I have a 1m3 tank of air at 100 psi, they are going to release to a 1m3 tank which has air at 5 psi. There is a meter long pipe connect between two tanks. How to calculate the flow speed ratio ...
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3answers
789 views

Temperature change inside pressure chamber

Let's say there is a pressure chamber with some sort of sample / specimen (e.g. protein crystal) in it. Now I apply a certain amount of gas pressure, e.g. 10 or 20 atm. Let's say I use xenon as a gas. ...
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2answers
56 views

One Particle in a Vacuum

I recently watch a lecture by Neil Tyson where he said the closest thing we have to a vacuum is interstellar space. I believe he said there will be one atom per 1 cubic meter or something close to ...
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1answer
9k views

How much work is needed to compress a certain volume of gas?

I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
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1answer
297 views

What could I test for in a guillotine? [closed]

I'm doing a school assignment project and I need to investigate something of my choice. I was thinking of doing something about how the height and angle the blade of a guillotine is dropped from ...
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2answers
2k views

Why the pressure of atmosphere doesn't crush you when you e.g. walk outside?

Why the pressure of atmosphere doesn't crush you when you e.g. walk outside? I mean the density of air is $1.26 kg/m^3$, so with $100 km$ above us, it exerts much pressure on you when you walk ...
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1answer
13k views

To calculate pressure at point in a vertical water pipe of given diameter

Is it possible to calculate pressure at a point in a pipe, where a solenoid valve shall be placed, given that the pipe carries water (utility supplied, regular water) from an overhead tank (at a ...
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1answer
23 views

How to find the force due to fluid pressure over a surface?

The question is about sphere like surfaces, like the hemispherical base of a cylinder as shown. The cylinder is filled with fluid till the given height $h$, and the density of the fluid is $\rho$ ...
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1answer
38 views

Work needed to pump the balloons

Let's suppose that we want to pump the balloons underwater from the initial volume $V_0$ to the volume $V_1$. The pressure there equals $p_1$ and the atmospheric pressure is $p_0$. It is claimed ...
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1answer
41 views

How does the Cross section of a toy hovercraft affect on the time that it hovers? [duplicate]

My question is about a toy hovercraft - a balloon connected to a CD. I need to know about something. How does cross section of the pipe affect the time that the toy hovercraft hovers above the ...
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1answer
17 views

what’s the water pressure at the surface of earth in Kpa? [closed]

I need to know this to solve a problem, but cannot find information on it.
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1answer
26 views

Capacitive pressure gauge under a change of pressure

I have seen in an article, that a capacitive pressure gauge made of two parallel plates with a dielectric material between with constant $K$ under an increase of pressure $\Delta P$, a Young´s modulus ...
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2answers
57 views

hydrostatic pressure on a plane surface

I've been trying to calculate the amount of pressure on a wall of a rectangular structure, that is under sea watter. For example a dam. I can't come to see any example to be able to locate the ...
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1answer
76 views

How to calculate the increased pressure drop due to a restriction?

Assume I have a straight pipe with diameter D1 and a volumetric flow, Q flowing through it. The inlet pressure is P1 and the outlet pressure is P2. Now, assume I've added a restriction in the middle ...
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1answer
17 views

What is an expression/physical law that relates high frequency thermal fluctuations to gas pressure?

When a gas is compressed the 'ideal gas law' can predict what the increase in gas temperature will be. But that's just a mean temperature, right? At a quantum level the frequency of molecular ...
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1answer
32 views

Height dependancy when adding volume from below to a fluid column

Suppose there is a fluid column of height H and there is a screw already inserted from outside the column entering through the bottom of the column. The screw has a total length L and only 0.1*L is ...
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1answer
47 views

What forces act on an object submerged in flowing fluid in an enclosed environment (i.e pipe)?

Let's say we have a pipe with water flowing through it and obstacle is inserted into the pipe and is rigidly fixed to the inner wall so that it does not get washed away. What forces are exerted by ...
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1answer
58 views

Properties of Fluids-theoritical confusion

I am having a very basic confusion on how we calculate the height of atmosphere when we assume that the density does not change with altitude(density remains 1.29 kg/m$^3$). I want to know why we say ...
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1answer
82 views

The Bernoulli equation: positive and negative sign problem

According to bernoulli equation $$ P_1+1/2 \rho v_1^2+ \gamma h_1= P_2+1/2 \rho v_2^2+ \gamma h_2. $$ Because $$ v_1=0\quad h_1=0 $$ So $$ 0= 1/2 \rho V^2+ \gamma h. $$ It is wrong I know, but ...
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2answers
33 views

About using screw in air compression and air Engine [closed]

I want to use screw to build compressed air engine, as following image As I designed, this screw rotate in a tube My Question is: How successful this idea? Note: If this question not related to ...
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2answers
73 views

Possible solutions to the crown problem of Archimedes [closed]

My teacher was talking about the crown problem, possibly solved by Archimedes using skills about density, weight and other properties that he studied. In the original publication, by Vitruvius in a ...
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2answers
87 views

Why liquids in hydrostatic equilibrium stay at the same height? (open tubes)

This part of the book says that, because the two liquids have the same pressure at the same height (that's true), then if a liquid has a higher height, the liquid would have more pressure at a ...
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1answer
54 views

How much pressure do wheels exert on the ground?

I would like to know how much pressure 4 "rigid" wheels (as opposed to tyres) would exert on the ground; I've been on the case for hours now and the best I've come across to calculate this was the ...
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3answers
99 views

How do we measure pressure above a liquid column?

Consider this point $A$, just at the surface of any liquid exposed to atmosphere. The hydrostatic pressure exerted by this liquid of height $h$ is $h\rho g$. My confusion is tha that this pressure ...
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1answer
100 views

Pressure inside a plastic bottle filled with water and squeezed by X weight?

I'd like to know how it'd be possible to calculate the pressure inside a plastic bottle filled with water and squeezed by say 20 kg sitting on the bottle, which is lying on its side (so that ...
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2answers
160 views

Definition of pressure in Bernoulli's principle

I have a difficulty to understand Bernoulli's Principle which states increased fluid speed decreases the pressure. But in a wind tunnel when we measure the pressure with a pitot tube, both the ...
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1answer
120 views

Hydraulic scissor jack lifting capacity

Can you please assist with a really simple question? I have a hydraulic scissor jack table with the following: 2 hydraulic cylinders, each with a cylinder stroke of 240mm, a cylinder bore of 50mm ...
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3answers
769 views

Does the entropy of an adiabatically isolated system stays the same after we decrease/increase the pressure?

Even if the system is isolated and there is no heat exchange with surroundings, shouldn't the decrease/increase of pressure result in increase/decrease of entropy? Does this property of an ...
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1answer
33 views

Convert pressure to energy [closed]

I read a little about electricity being created from pressure, Piezoelectricity. I'm still pretty newbie about it though. Let's say I want to charge a battery from that technique, using my hands to ...
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1answer
46 views

(air pressure and displacement) Isn't this image wrong?

Isn't this figure wrong? P(x,t) = -B(dy/dx) . If the derivative of air displacement has a maximum, then this is where the pressure is minimum, not maximum as this figure suggests. Could someone ...
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1answer
230 views

wall thickness for a very large, low-pressure vessel?

I'm working on a space colony simulation, and I'm at the point where I need to calculate the thickness of the habitat walls, as a function of air pressure and geometry (and assuming some common ...
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1answer
33 views

What is the purpose of sensors and pumps with less than 1 ATM pressure?

This question is not directly a physics questions, though related a little. Previously for sensors, and currently for air pumps, I am doing some research. I have found a digital pressure sensor on ...
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1answer
34 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 ...
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2answers
257 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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1answer
2k views

Compressed air in a volume: Can I determine its temperature?

Using a compressor, I augment the pressure in a volume (using atmospheric air). I only measure the pressure inside. I now that the density will increase however, the temperature decreases. Can any one ...