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## Hot answers tagged pressure

7

The physical processes that control the structure of conical piles are fascinating and imperfectly understood even today. However we can approach your question in approximate way. The angle that the surface of the pile makes with the ground is called the angle of repose. Predicting this theoretically is hard because it is is sensitive to the exact nature of ...

5

Your analysis and intuition are correct. The force needed in the second setup is larger, even though the weight of the water is the same. To understand why, consider the horizontal part of the container, $0.5\ \text{m}$ off the ground. This wall is above the water, so the water's pressure pushes up on it. Then in reaction, the wall pushes down on the water, ...

3

The micron used in this way is a unit of pressure. It's short hand for "micron of mercury". It's the pressure that causes the column of mercury in a mercury manometer (pressure gauge) to rise one micro meter. One Torr is one millimeter of mercury, and atmospheric pressure is 760 Torr. 1 $\mu$ = 0.133 Pa.

3

This is really three separate questions. Static and dynamic pressure: It is the static pressure that really matters in practical situations. The dynamic pressure is related to the kinetic energy of the fluid which, when it changes, causes a corresponding change in the static pressure. Condenser/evaporator application: The basic Bernoulli equation ...

2

The argument in the video seems flawed: it is true that the surface area has increased, but that is irrelevant, because when you calculate pressure you look at the number of molecules hitting a unit of area, which depends on the gas density, and here on the volume, but not on the total area. The derivation is made here: https://en.wikipedia.org/wiki/...

2

As you increase the surface area you must bring parts of the surfaces closer together and this will increase the rate at which the surfaces are hit by the molecules which will compensate for the increase in area.

2

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 fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same. Due ...

2

A few clarifications on this thread in case anyone is reading in the future and is getting confused. I know however, that the temperature did in fact change, hence it's not an adiabatic process. That isn't really how an adiabatic process is defined. The temperature can change within a system (and often does) and it still be adiabatic. An adiabatic ...

2

The pressure drop shown in the pipe in situation 2 is based on an assumed flow rate, but that flow rate can't be achieved when the pressure is only 50 Pa. You cannot deliver a fixed flow rate and a fixed static pressure: when the flow rate is kept constant, like produced by volumetric pumps, the pressure will vary with resistance: if you block the exit the ...

2

In your approximation there is a velocity discontinuity where the pipe joins the container. Assuming that is a good approximation then you are correct and $P_a=P_b+\rho v^2/2$. In real life though, the pressure will change smoothly because the closer you get to the pipe, the larger the effect of the motion of the water inside the tank.

2

The force straining a grain (which may soon be squashed) is equal and opposite to the weight (gravity force) supplied by the grain pile above. That's Newton's third law. If ALL the weight of the pile were held up by one single kernel, F_grain ~= Mass_of_pile * g and it would be easy for the ton of grain to smash the bottom kernel. It doesn't work ...

1

Using Bernoulli's equation and the momentum conservation equation, we can show that water flowing out of a pipe with cross-section $A$ at speed $v$ exerts a force $F$ on a wall (at 90 degrees), acc.: $$F=\rho Av^2$$ With $\rho$ the density of the water. But your specification of "8" pipe with 500psi stream of water exiting it and hitting a wall at 90 ...

1

You need to get $p_4-p_3$. Taking the datum of elevation z as that of points 3 and 4, we have $$p_{atm}+(10)\rho g=p_2+\frac{1}{2}\rho v^2$$ $$p_3+\frac{1}{2}\rho v^2=p_2+\frac{1}{2}\rho v^2$$ $$p_{atm}+(120)\rho g=p_5+\frac{1}{2}\rho v^2+(120-h)\rho g$$where h is the depth of point 5 below the surface of the tank on the right. $$p_4+\frac{1}{2}\rho v^2=... 1 Even if you call the term dynamic pressure, and has units of pressure, it is not a pressure at all. It is a necessary contribution to the total static pressure, though, And it is the static pressure that matters when you move a piston in a gas. The static pressure is also related thermodynamically to the temperature, in the first case as the average ... 1 This is a correct way to solve exercises involving viscosity (within certain constraints, e.g., constant viscosity). Eqn. 1 is a version of the Bernoulli equation, modified to include a frictional head loss, and is definitely valid, provided the velocities used are the average velocities. Eqn. 1 without the h_L is valid along a streamline, even for a ... 1 A reversible process is characterized by a continuous sequence of thermodynamic equilibrium states for whatever system you are considering. So, for your system to experience a reversible process, its pressure and temperature must differ only slightly from that of its surroundings throughout the entire process. And there can be no spatial temperature or ... 1 It depends on what you consider to be the system. If the system is the entire container, then there are no thermodynamic operations, quasistatic or not, on the system by the external environment. And as you said, the system is not in thermal equilibrium. If you talk about a thermodynamic operations you need to define a system and an environment, in this ... 1 Difference between real and absolute value in general: Look at count_to_10 's answer. For acoustics and preasure measurement: Absolute pressure - pressure against perfect vacuum. Real pressure: Usually defined as the pressure against a reference-environment. Also called differential pressure. For example the pressure of the air inside a football against the ... 1 Your guess is correct. I think you are expected to assume that a is sufficiently far from the hole that v_a=0. If the question does not ask you to make this assumption you should state it explicitly yourself. It does not follow that there is a discontinuity in velocity at the hole just because there is a discontinuous change in cross-section. ... 1 It depends what work you refer to. If it is the work made by gas B on the piston at the right, then this work is -P\Delta V because the length the piston moves is given by the change in the total volume (regardless of the motion of the other piston). This will be also the net work done on the system A+B. To compute the net work by gas B you need to add ... 1 You can check your answer by figure below:$$\Delta V_B=S(x_{B,2}-x_{B,1})-S(x_{A,2}-x_{A,1})= \Delta V-\Delta V_A$$1 The Bernoulli equation inherently takes into account the fact that the flow approaching the exit hole is converging toward the exit hole and thereby accelerating. So the pressure in close proximity to the exit hole (within just a few exit hole diameters away) is decreasing while the flow velocity is increasing. This is how the pressure decreases from ... 1 It's because the centre of buoyancy and centre of gravity don't necessarily lie on the same point. This creates two types of mechanical equilibrium: stable and unstable. It turns out that when a human body is floating with its face inside the water, the body is in stable equilibrium. That is because in that position, the centre of gravity lies below centre ... 1 Turns out it's more of a bio question. https://www.google.com/search?q=why+do+dead+people+float&oq=why+do+dead+people+float&aqs=chrome..69i57.6523j0j1&sourceid=chrome&ie=UTF-8 As for the head part, your head (mainly your brain) is more dense than water. 1 Vacuum or pressure is quantified in terms of bar or torr. 1 bar or 760 torr is roughly one atmosphere and in terms of vacuum measurement 1 mili-bar is taken as almost equal to 1 torr. at 1 bar pressure and at room temperature the number of atoms per cc is ~2\times 10^{19}. The number of particles per cc in vacuum can range from 10^{-4} to 10^6. The ... 1 It's the volume that determines the pressure (for a given amount of gas at a given temperature), so if you consider a rectangular container, increasing the surface area of two opposite sides and/or increasing the distance between those sides will increase the volume and therefor decrease the pressure. But increasing the total area while keeping the volume ... 1 The stress induced in a pipe by internal pressure is$$P_r \over t$$where P is the applied pressure, r the pipe radius and t the pipe wall thickness. The strain induced in the pipe wall is$$\Delta r \over r$$where \Delta r is the change in radius. The basic stress strain relationship is$$\sigma = E \epsilon where $\sigma$ is the stress, \$...

1

Plungers are more effective when pushing water instead of air because water doesn't compress. If you let the bell of the plunger fill up with water before thrusting, you have a "solid" column of water from the plunger to the clog. Thrusting the plunger moves column of water like it was a solid piston and applies the entire force of the thrust against the ...

1

The movement of the "dookey" is caused by pressure created from a snug, well fitted toilet plunger. When you press and and lift the plunger, it pushes and pulls the dookey. Rocking it back and forth until its free. So there is pressure when you push, and suction when you pull.

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