All Questions
Tagged with definition pressure
32 questions
0
votes
2
answers
39
views
Is pressure only define at the surface in contact?
Is pressure only defined at the surface of an object or a container in contact with the fluid as per the definition of pressure,
Pressure is the force applied perpendicular to the surface of an ...
4
votes
1
answer
537
views
Clarifying the definition of pressure in statistical physics
I am studying David Tong's lecture note on statistical physics, and I have a question regarding the precise definition of pressure. I checked other postings in this community, but was unable to get ...
- 173
0
votes
1
answer
45
views
Pressure sensors vs. piezoelectric sensors
In simple terms, what is the difference between pressure sensors and piezoelectric sensors?
I did some google search online and could not come to a good conclusion.
Say you make a 'sensor' in the lab ...
4
votes
2
answers
552
views
Is temperature held fixed in this derivative for pressure?
In Ashcroft and Mermin, they use the thermodynamic identity
$$P = -\left(\frac{\partial E}{\partial V}\right)_N$$
to compute the pressure of an electron gas. Is temperature $T$ also held fixed here?
- 1,261
1
vote
4
answers
972
views
What is constant in an isobaric process, internal pressure or external pressure?
I was taking a course in thermodynamics, where the instructor started to derive the formula for work in case of isobaric process for an ideal gas
It stated W = -∫ P_ext dV
And then equated it with -∫...
0
votes
0
answers
329
views
Why is bulk modulus positive in equilibrium?
$B=-PV/\Delta V$ The negative sign indicates that when pressure increases, the volume
decreases. That is, if $P$ is positive, $\Delta V$ is negative. Thus for a system in
equilibrium, the value of ...
1
vote
3
answers
515
views
In reversible process, why define $\delta W=-PdV$ instead of $\delta W=-VdP$?
For a reversible process, it is assumed that the external pressure $P_{ext}$ is infinitesimally different from internal pressure $P_{int}$.
So in reversible process, I can have $~P_{int}=P(V,T)~$ but ...
- 243
1
vote
1
answer
1k
views
What's the difference between normal viscous stress and pressure?
The stress tensor on a fluid element is the following:
The diagonal terms in the two tensors $-p\textbf{I}$ and $2\mu\textbf{e}$ are both stresses that act perpendicular to the faces of the fluid ...
0
votes
2
answers
2k
views
What is the general formula of work in terms of pressure and volume?
I've seen work often represented by the formula $$W = PΔV$$
But there are also other formulas, which represent different types of work. For example,
Non Flow Work
$$ W =\int_{1}^{2} PdV $$
Steady ...
- 105
0
votes
1
answer
929
views
What is air pressure and is it the same as atmospheric pressure?
What is air pressure and in particular is it the same as atmospheric pressure? Can the terms be used interchangeably, and why are there different instruments to measure the two properties?
5
votes
2
answers
592
views
How do we know sound pressure squared is proportional to the power in the sound wave?
I am trying to find the equation that explains why we can say the pressure exerted by a wave (squared) is proportional to the power. I see this claim made a lot but I can't tell where it comes from.
- 151
1
vote
1
answer
76
views
Pressure Equation Clarification
$$\text{pressure} = \frac{\text{force}}{\text{area}}$$
Does pressure in this equation refer to the gauge pressure or absolute pressure?
- 409
1
vote
0
answers
47
views
Fluid dynamics and Bernoulli equation
What is the basic difference between static, dynamic and hydrostatic head in bernolli equation?
Is static pressure gauge pressure or thermodynamic pressure?
0
votes
2
answers
814
views
Value of temperature at normal temperature and pressure (NTP)
I was attempting this numerical from my textbook:
"A definite mass of an ideal gas at NTP is allowed to expand to four times its original volume i) slowly, ii) suddenly. Calculate its final ...
user236322
1
vote
1
answer
1k
views
What is the physical meaning of static and velocity pressure?
According to Bernouli's equation, the static pressure inside a pipe with streamline and steady flow decreases with fluid's velocity. One explanation to rationalise this phenomenon is because velocity ...
- 817
0
votes
2
answers
416
views
How is fluid pressure defined?
In general, the pressure $p$ due to force acting on a surface of area $A$ perpendicular to it is defined as
$$p=F/A$$
assuming that the force is distributed uniformly over $A$. Otherwise, we can ...
- 972
4
votes
1
answer
2k
views
What is fluid pressure?
I cannot understand the concept of fluid pressure.
Consider a liquid molecule at some point inside a liquid vessel. All the other molecules which are in contact with this molecule will exert normal ...
- 646
0
votes
1
answer
633
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 ...
- 303
1
vote
2
answers
838
views
What is the "pressure on a point" precise definition?
I'm reading Landau's Fluid Mechanics and in the first page is defined the pressure in every point and every time: $p=p(x,y,z,t)$. Here every "point" $(x,y,z)$ is really a tiny differential volume $dV$ ...
- 584
0
votes
2
answers
1k
views
How can we define "Pressure" as a tensor?
We usually see in elementary textbooks that the quantity "Pressure" is taken as an scalar. But I heard it's actually a tensor and didn't hear anything more.
How can we define $P=\frac{F}{A}$ as a ...
- 872
2
votes
2
answers
6k
views
Pressure in the stress tensor?
The stress tensor can be written as:
$$\sigma_{ij}=-p \delta_{ij}+\sigma'_{ij}\label{1}\tag{1}$$
where $\sigma_{ij}'$ is called the extra stress tensor.
From what I understand pressure is pressure ...
0
votes
2
answers
197
views
Definition of isobaric process
I have a doubt on the definition of isobaric process in thermodynamics, which of the two is the correct?
$(A): \mathrm{d}p=0$ (there are no variation of pressure during the process at all)
$(B): p_{\...
- 2,637
3
votes
2
answers
1k
views
Difference between two types of pressure
When I first studied thermodynamics the concept of pressure was defined by means of the fundamental relation $S = S(U,V,N)$ for simple systems. The pressure was thus defined by
$$P = -\left(\dfrac{\...
- 37.4k
1
vote
0
answers
126
views
Pressure of water in all directions [duplicate]
As far as I understand, pressure acts downwards on a surface of a body in water because pressure $P$ is given by
$$
P = \frac{F}{A} = \frac{m \, g}{A}
$$
where $F$ is the gravitational force on the ...
- 75
8
votes
4
answers
11k
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 = \frac{F}{A}...
user94491
1
vote
2
answers
4k
views
Can pressure be negative? [duplicate]
From Wiki and from physics fundamentals lections I received info that pressure is scalar value. But in definition you have relation between projections of two vector values to normal axe-force and ...
10
votes
5
answers
58k
views
What is basically the difference between static pressure and dynamic pressure?
What is basically the difference between static pressure and dynamic pressure?
While studying Bernoulli's theorem, I came before these terms. The law says:
When the fluid flows through a small area,...
user36790
0
votes
2
answers
1k
views
How many psi's are in one bar?
6894.7573 bar = 100000.0 psi according to google
6894.7573 bar = 100000.0001 psi according to wolfram alpha
which is it? How many psis are in one ...
- 183
3
votes
6
answers
2k
views
Mathematical Reasoning for Fluid Pressure as a Scalar
This question from a while ago and answers/comments to this question from earlier today both make heavy mention of the fact that fluid pressure is a scalar. Although this information was surprising ...
- 2,993
3
votes
1
answer
626
views
Rigorous definition of pressure in a fluid
We briefly introduced some terms at the start of my Fluids class, and one of them was pressure. I'm looking for a rigorous definition of pressure.
Wikipedia gives this definition for pressure: $p = \...
- 390
34
votes
8
answers
151k
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?
- 1,455
11
votes
4
answers
11k
views
Define Pressure at A point. Why is it a Scalar?
I have a final exam tomorrow for fluid mechanics and I was just looking over the practice exam questions. They do not provide solutions. But pretty much I have to define pressure at a point and also ...
- 1,158