Questions tagged [pressure]

This tag is for questions relating to pressure, in the physical sciences, the perpendicular force per unit area, or the stress at a point within a confined fluid.

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Latente heat in pressure cooking

When discussing why cooking is faster in pressure cooker, the usual explanation (including on SE) is that higher pressure allows reaching higher temperatures before water starts boiling (typically 120°...
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Range of water undertow in a differential pressure ($\Delta p$) situation

I hope this is the right forum for it (otherwise I'll happily move my question to the correct one). I recently read about a number of diving incidents involving a delta p situation. All those reports ...
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Pressure of a system at the thermodynamic equilibrium

I'm reading a book in which it says that a system is at mechanical equilibrium if the pressure is constant in time but not necessarily uniform in space at any fixed point (for example it can be caused ...
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Would a human be able to descend to depths in the ocean that would crush their body?

Would not the same forces that would crush the body also resist descent? Or would the body be too buoyant to descend below the point at which the water would crush a human?
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In terms of compressive stress $F/A$, what is the cross-sectional area of a sphere?

Any physics textbook chapter on stress-strain curves will generally mention that stress is force acting upon an area, and when a shape is three-dimensional, that area is the cross-sectional area. ...
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199 views

Does water pressure have any effect on the size of a permanent magnet's magnetic field?

If a permanent magnet is dropped into a deep body of fresh water such as Lake Superior, as it descends down, the rising water pressure should continually reduce the size of the magnetic field ...
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What does it really mean by "faster flow, lower pressure"?

My primary school physics textbook trys to brainwash me with the idea that a region in a fluid with fast velocity (often) has lower pressure than a region that flows slowly. Examples of this include ...
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Why water flow at high pressure from tap if we close its half portion opening and not maintaing equilibrium of low flow?

I am having a doubt that when we open a tap and a certain amount of water start coming out supplied by tank . When suppose I close the opening of tap half way so that only half mouth of tap is now ...
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Thermodynamics: Enthalpy to be determined at both pressure and temperature

I am having difficulty to find the enthalpy , hg. The statement goes like this: hg is the enthalpy in kJ/kg of water vapour at 0.07 bar atm and the flue gas temperature (176 °C) Maybe I didn't pay ...
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Why is a force distributed over an area? Why couldn't the stress be directly equal to the force?

So, my question might seem silly. I know in real life when we apply a force with our hand and push on lets say a cylinder , we know the force will be distributed over the cross section of the area, so ...
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How to calculate pressure exerted by a rocket's exhaust on a surface from a certain altitude?

How do you calculate the pressure that is exerted on a surface (say from a rocket engine) at an arbitrary altitude? For example, pretend I know the exit velocity and pressure of a rocket engine at an ...
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How to find at what rate of air flow the pressure in the system is maintained?

I have a pump that is pumping air into a vessel that has an inlet and an outlet. I have the experimental values for the point where the flow rate maintains the pressure but I can't figure out how to ...
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Mercury Barometer

Why Mercury surface is flat instead of convex at 760mm Hg level in Mercury Barometer? refer the image attached. note that At top it is a vacuum and surface tension = (pi-po)r/2.
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Pressure inside hot air balloon [duplicate]

I have formula $PV=nRT$. As temperature rises in hot air balloon why does pressure inside hot air balloon and outside are the same? I have thought about it for long time and I think due to air ...
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217 views

Hydraulic analogy and pressure in pipes

In the latest days I've been quite obsessed with understanding how electricity work through the hydraulic analogy. I still have some problems regarding how "voltage drop" works, and how pressure drops ...
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399 views

What does gauge pressure indicate in fluid flow?

In flow measurement, suppose we find gauge pressure difference between any two sections. Does this pressure is total pressure difference, I mean potential, kinetic and pressure head difference or only ...
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Can open-tube manometers be used to measure atmospheric pressure?

I was going through a slide made by my physics professor and was wondering about the statement made at the bottom: "This cannot be used to measure the atmospheric pressure". Why is that so? Given ...
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Bouyancy and Normal force at a fully submerged object [duplicate]

I learned as a child that in a fully submerged object (which is touching the bottom of the fluid tank), the normal force "N" by the tank's bottom to the object is ...
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4answers
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How does Upthrust/buoyant force act on an object?

I came across this question where, In a container there's water at the bottom , kerosene on top and an ice cube floating between them and I was asked to calculate the ratio of height of cube in ice to ...
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Doesn’t the incompressibility of a liquid prevent external pressure to be spread throughout it? [duplicate]

Doesn’t the incompressibility of a liquid prevent any pressure exerted on it to be equally distributed throughout it? For example, when the atmosphere pushes on a liquid, how does the pressure due to ...
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644 views

Density solver for ideal mixture of real gases

I am referring the paper on GERG-2008 equation of state. I am interested in calculating the properties of ideal mixtures of real gases. The GERG-2008 EOS is in Helmholtz free energy and hence the ...
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How to express pressure variance in the canonical ensemble of statistical mechanics?

The variance of pressure can be written as $<p^2> - <p>^2$. What is another way to express this? I found $\left<(p-<p>)^2\right>=\frac{k_B T^2}{C_v}\left(\frac{\partial P}{\...
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Why does pressure in a thermos increase after shaking up hot water and soap?

Whenever I wash my thermos, I put hot water and then some soap in; then I seal the one end with my hand or use the lid. After shaking it up, if I slowly remove the lid or my hand, it expels a little ...
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If I take a bottle of air into space, and open it, then close it and come back to earth and open it one last time, what would happen?

I was reading this post, but no one seem to go further as to say what would happen if you brought the bottle back to Earth? Another thing I want to know is, what would now be in the bottle?
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Why is the force due to a vacuum in a syringe so much greater than the force due to the air being compressed in the syringe?

I'm a teacher using a plastic syringe (no needle) to demonstrate the compressibility of air and the incompressibility of water. Works great, they can push the plunger in while blocking the end of the ...
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Why does a ball come out on blowing into the bottle?

I take a ball smaller than the mouth of the bottle and blow into the bottle (The bottle is horizontal). When I blow I create a low pressure, outside the bottle at the mouth and there is high pressure ...
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Hydrostatic pressure in closed conduit vs open chanel flow

I am still confused and have questions: In closed conduit flow, the pressure at bottom or middle point of steady flow fluid can be caculated from hydrostatic pressure as the case in open chanel steady ...
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Why doesn't the formula for the entropy change of an isobaric process include a work term?

I tried to derive the entropy change of an isobaric process and arrived at: $\Delta S = C_pln(T_2/T_1)+nRln(V_2/V_1)$ However, it appears the answer is just: $\Delta S = C_pln(T_2/T_1)$ It seems like ...
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Tire pressure and its effects

My textbook reads as follows:- "Tire pressure is important for the safety and durability of automobile tires. Too low a pressure causes large deflections and the tire may overheat; too high a ...
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Why is the buoyant force of some object equal to the gravitational force of the fluid displaced? [duplicate]

I’ve done the derivation for the buoyant force using the difference in pressures and after everything is said and done the buoyant force of some object in a fluid is equal to the gravitational force F=...
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430 views

Why does air get trapped below water pouring into a glass?

The drinking-water-tap at my workplace has a low pressure continuous stream of water. When I pour water into a glass which has at least about (depth) 5cm of water in it, surprisingly large air bubbles ...
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Why does the Pascal's barrel experiment need a tall column of water?

This question is based on the content of this video . The experiment consists of putting a tall, thin column of liquid on top of a barrel filled with water, so that the pressure caused by the large ...
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Why is the rate of evaporation higher, if the air pressure is lower?

In an open pot,the molecules of water can get the kinetic energy to free themselves from the intermolecular force and evaporate from the air molecules that are over the surface of the water are ...
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Direction of dynamic pressure

While walking near the river I've noticed something interesting in the water. There's a nice autumn here and tree leaves was falling and accumulating on the bottom of the river. But I was surprised ...
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The relationship between the pressure at the base of a container and the normal reaction on the container

This is NOT a homework question. The question here is just an example. In this question, after both the liquids are mixed and a homogenous mixture is created, I found the effective density of the ...
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Why doesn't an object with less density than a fluid float 100% above the fluid level?

If an object is less dense than that of a fluid, then why doesn't it float completely over the fluid level? Why does some part of the object remain submerged in it? Can there be an object that can ...
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Why is the work a function of the mass's pressure?

A gas is confined in a closed container with a movable piston. The container is kept in a hot water bath. Blocks of different known masses are placed on top of the piston one at a time, and the gas is ...
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Calculating the Absorbed Heat & the Change in Internal Energy of an undefined thermodynamic process

In the given figure of a P-V diagram, the process from $T_2$ from $T_3$ (the hypotenuse part of the triangle) doesn't follow any of the 4 thermodynamic processes (i.e Isothermal, Isochoric, Isobaric, ...
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How to calculate outward pressure of water tank with salt in it?

I'm building a flotation tank. To make the frame, I'm thinking of just using wood (10 cm by 10 cm treated pine). like in the design attached. And connecting the pieces of wood with metal brackets and ...
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Static pressure in a free jet

I am asking essentially a follow up to this very good question and answer Static Pressure in a Venturi vs a Free stream And this Is the static gauge pressure of a free jet always atmospheric? If I ...
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1answer
350 views

Pitot tube and the assumption of hydrostatic pressure distribution

We have water flowing in an open channel. A small tube is placed in the channel, and the water raises to a height $l$ above the water surface. The distance from the water surface to point $1$ OR $2$ (...
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590 views

Difference between Pressure and Pressure Energy in fluids

For a fluid with viscosity to flow through a pipe that has the same cross-sectional area at both ends, at a constant velocity, there has to be a pressure difference according to Poiseuille's Law. Why ...
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Conceptual understanding for pressure inside incompressible fluid

I'm was thinking about incompressible fluid and how pressure effects it and I came across this idea that I'm not sure if it's correct. I would like some correction along with my current understanding. ...
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Work done by force due to internal pressure of liquid drop

I am extremely puzzled in the situation mentioned below, which is a problem of Excessive Pressure in Liquid Drop. This is my question: A liquid drop exerts a pressure on walls of the drop, and the ...
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How to estimate change in refractive index due to acoustic wave travelling in quartz?

I'm studying acousto-optic modulators and the basic principle of operation is that an acoustic/sound wave is made to travel along one direction of a crystal (say quartz). This creates a pressure wave ...
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How to calculate acoustic impedance of a megaphone?

I'm working on a physics problem that asks how a passive megaphone (simple cone shape) can optimise the transfer of the human voice, compared to not using one at all. I understand that some of this is ...
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How to calculate air flow from a pressurized tank?

I am writing an app that deals with simulated air brakes, and I need to simulate the release of air from one container of a given pressure into another container of a lower pressure. It doesn't have ...
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$\rm CO_2$ Pressure Enthalpy Diagram In Programming

Im trying to make a 1D model of $\rm CO_2$ cooling in Python. What I'm currently stuck on is programmatically reading a PH diagram. I have a bottle of $\rm CO_2$, which is vented to the atmosphere via ...
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Are low pressure and high pressure areas responsible for rain?

My understanding is that low pressure areas are susceptible to rain. However, high pressure areas have no rain. Now, I want to correlate this with the following areas - Lower Hutt, Wellington , NZ - ...
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Would a pressurized container move by itself if opposite edges have different size surface area?

If inside a closed container there is gas with higher pressure than outside the container, and one edge of the container has a larger surface area than the opposite side, would the container move by ...

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