The tag has no wiki summary.

learn more… | top users | synonyms

-1
votes
0answers
17 views

Conductor in electrostatic equilibrium

Consider the following capacitor: The upper conductor is charged by $Q$. There's a conductor on the middle with thickness $e$. The lower conductor is connected to the ground. All of them have area ...
0
votes
1answer
40 views

Boltzmann equation collisional operator in thermal equilibrium

Edited after Thomas' answer http://jila.colorado.edu/~ajsh/astr5770_14/grbook.pdf#section.30.5 Question 30.6. "Detailed balance": System is in thermal equilibrium, and the physics of the system is ...
-1
votes
1answer
35 views

Exercise about equilibrium and virtual work [closed]

Two railway carriages of mass $M_1=2m$ and $M_2=m$ are on a 45° inclined plane. A spring, parallel to the plane, keeps both carriages in balance against the gravitational accceleration. The ...
-1
votes
0answers
20 views

Principle of virtual work - Equilibrium [duplicate]

Two railway carriages of mass $M_1=2m$ and $M_2=m$ are on a 45° inclined plane. A spring, parallel to the plane, keeps both carriages in balance against the gravitational accceleration. The ...
1
vote
1answer
55 views

Why can't charge be in a stable equilibrium in electrostatic field?

I am reading Feynman's Lectures volume_II where he discussed the impossibility of the presence of stable equilibrium in an electrostatic field. There are no points of stable equilibrium in any ...
0
votes
1answer
18 views

Total Collapse in Understanding a Pulley

In the following system, the tension T is equal in magnitude to the weight W. But how can I set this up in a system of equations? This is my problem: $\Sigma F=0=\left( \begin{array}{c} 0\\ -W\\ ...
2
votes
0answers
38 views

Local and global detailed balance

I'm taking a course on nonequilibrium statistical mechanics and I encountered the terms local and global detailed balance. I'm a bit confused about what is their exact definition and what is the ...
3
votes
0answers
37 views

Is it possible to have a line rather than a point where the three states of a substance can exist?

Most of us are familiar with state diagrams that define which of the three states a substance will take given the pressure and temperature. And that some substances, such as water for example, exhibit ...
2
votes
1answer
51 views

Why should slope of pressure versus volume always be negative?

I read that the slope of the pressure, ($P$), versus volume ($V$) graph should always be negative for thermodynamic stability, but there was no further explanation in the text. Could someone give an ...
1
vote
1answer
77 views

Mechanical equilibrium : thermodynamics and classical mechanics

A similar question was asked here but mine is a bit different. In thermodynamics, a mechanical equilibrium is defined as a uniform pressure (for a fluid). In classical mechanics, equilibrium is ...
2
votes
2answers
61 views

Where do forces point in an equilibrium system

I have the system above, with three identical balls of weight $W$ and radius $r$. The angle joining the centres is $\theta$, and the coefficient of friction between the balls and the plane is $\mu$ ...
1
vote
1answer
109 views

How to calculate the normal force exerted by a fulcrum off-center?

So I know that $F_N$ exerted by a fulcrum right under the centre of mass for, say, a long horizontal rod, is equal to $mg$. But what if the fulcrum is off the centre of mass either to the right or the ...
0
votes
1answer
55 views

How many bricks can be put without disordering the equilibrium? [closed]

A homogenous brick with length L, is on a horizontal surface. On this brick are put one after another other bricks, which are the same with the first. Every brick is moved along L/5 units horizontally ...
0
votes
2answers
113 views

Checking for equilibrium in a square configuration of charges [closed]

Four equal positive charges each of magnitude q are placed at the respective vertices of a square of side length l. A point Q is placed at the centre of the square. Then find the state of equilibrium ...
0
votes
2answers
64 views

$N>2$ gravitating masses can never reach equilibrium [closed]

If you have $N>2$ point masses, each attracted to each other by the force of gravity, how could you go about showing that they will never reach equilibrium?
1
vote
1answer
43 views

Equilibrium when it shouldn't be?

I'm doing an experiment that requires me to balance a ring, tied to four strings, in the middle of a force table; in other words, the objective is to set the ring at equilibrium. Each string is ...
0
votes
1answer
62 views

Rotational Equilibrium Problem [closed]

The question is as follows: One end of a uniform 4.0-m rod, whose weight is w, is supported by a cable that makes an angle of 37° with the horizontal. The other end of the bar rests against a wall ...
0
votes
1answer
45 views

Temperature in a vacuum made in the lab

Is the thermal energy of a vacuum 0? And, how close to a perfect vacuum can we make in the lab?
0
votes
0answers
29 views

Deriving the Force on an ion in the Classical Harmonic Crystal

I was following Solid State Physics by Ashcroft and Memrmin and their introduction to the Classical Theory of the Harmonic Crystal. (Chapter 22) If there are a large number of ions in a straight ...
0
votes
1answer
35 views

Will heating water vapor induce equilibrium?

What happens to the vapor content if a mixture of gases saturated with water vapor is heated isobarically? Will the amount of liquid water present decrease, yielding up more vapor so as to ...
0
votes
1answer
86 views

Find the center of gravity of a system with three spheres [closed]

Three spheres are put on a table. The first sphere, whose mass is 1 kg is 20 cm away from the second whose mass is 2 kg and the third sphere is 100 cm away from the first sphere and has a mass of 5 ...
0
votes
0answers
38 views

Number of particles in a box at thermal equalibrium

Consider a cube box of volume $V$ in thermal equilibrium at temperature $T$. We have 3 pieces of information: The probability of finding a particle of mass $m$ in the box having momentum in ...
0
votes
2answers
59 views

What is the theoretical instantaneous temperature of a gas?

When we measure the temperature of a gas we typically integrate the molecular collisions and wind up with an 'average' temperature due to the sensor comprising a relatively large thermal mass. And ...
0
votes
1answer
44 views

Chemical reaction A+B$\leftrightarrow$C. Equilibrium VS Non Equilibrium

Could you please confirm or say why I am wrong? Let us consider the steady state of the chemical reaction $A+B \leftrightarrow^{k_+}_{k_-} C$, with $k_+$ and $k_-$ the forward and backward rates. ...
0
votes
1answer
79 views

Is equilibrum condition consequence of second law of thermodynamics?

Equilibrum state is generally stated to be most stable state. Is equilibrium state consequence of second law of thermodynamics at microscopic level. i.e a system tends to reach the equilibrium state ...
1
vote
5answers
210 views

Why am I not accelerated by the reaction force applied by Earth on me? [duplicate]

Newton's third law says that "to every action, there is always an equal but opposite reaction". And Newton's second law of motion says that, $F=ma$ $=>$ $a=\frac{F}{m}$. People says that If I stand ...
1
vote
1answer
85 views

What is thermodynamic equilibrium?

The state of thermodynamic equilibrium is typically defined referring to the system's behaviour in the future. Can the definition be formulated in terms of measurable quantities?
1
vote
0answers
42 views

Is the system in equilibrium?

If the time derivative of the Liapunov functional related to free energy of my system is zero, can I say my system is in chemical equilibrium?
2
votes
1answer
104 views

Extension of Lami's theorem

I was experimenting with the triple scalar product and forces in equilibrium when I came to this result: Consider 4 forces $ \pmb{F_i}$ for $i=1,2,3,4$. $\pmb{F_i}=F_i\hat{e_i}$ where $\hat{e_i}$ is ...
1
vote
2answers
118 views

Oscillations Near Equilibrium (With Linear Differential Equations)

Case I: The force acting on an object of mass m is $F(x) = F_o(1-e^{\alpha x})$ Case II: The force acting on an object of mass m is $F(x) = F_o(1-e^{-\alpha x})$ where $F_o$ and $\alpha$ are ...
1
vote
1answer
86 views

Balancing sphere

A cube is balanced on the very top of a sphere, and is given a small push in some direction, at which point it begins sliding down that side of the cube (due to gravity). Now, I want to keep the cube ...
3
votes
3answers
108 views

Average temperature of the universe

Is it possible to define some average temperature of the universe? If yes, what fixes this temperature and how t estimate today's temperature? Is it different from the temperature of the black-body ...
0
votes
1answer
46 views

simple physical system involving convergence to equilibrium at decreasing speed

I want to make an analogy of an economic model (Solow 1956) with a simple physical system that exists in reality. I am not looking for a mathematical formula to describe the system (I have that ...
-2
votes
2answers
200 views

Why are planets in unstable equilibrium in a stable orbit

It is well known that a planet in stable orbit is in unstable equilibrium. If e.g. the moon was just a few m/s slower in velocity, or a few m closer to the earth than it is, the gravity would ...
0
votes
0answers
158 views

Coefficients of Friction in Equilibrium Ladder Problems

A problem asked me to find the the minimum angle the ladder system could have while still remaining in equilibrium: If you want to examine my reasoning: Let's take the lower end of the ladder to ...
1
vote
3answers
357 views

Equilibrium using Center of Buoyancy and Gravity (Problem)

I don't understand a solution to a homework question. Specifically, I don't understand the logical sequence of each bolded statement in the answer. (b) To ensure that a ship is in stable ...
1
vote
1answer
130 views

Meaning of chemical equilibrium between two phases

Suppose two phases 1 and 2 of water, say ice and water, are kept in a closed container, at a fixed temperature $T$ and fixed pressure $P$? Then I have the following question: Is phase 1 in ...
2
votes
2answers
70 views

How's equilibrium possible here?

Here's the question.......Two point masses $m$ and $2m$ are attached at each end of a light rod. The rod is pivoted at the center and is free to move in a vertical plane. Then find the angle $A$ when ...
6
votes
1answer
115 views

Do the stars in a galaxy have a thermal kinetic energy distribution?

I think, there is practically everything given to that: many point-like masses, able to exchange energy pseudo-randomly, and far long enough time to reach a thermodynamical equilibrium. Of course, ...
1
vote
1answer
99 views

What is the cause for mechanical equilibrium in statistical mechanics?

In classical thermodynamics, mechanical equilibrium is defined as the state of a system in which there is no net flow of volume as there should be no net pressure within the system. Ok. ...
1
vote
0answers
46 views

I need to remove water from a system [closed]

I work in an industry and I need to remove water from a system. The scenario: There is a washer and a blower on a conveyor belt. The item being washed is plastic (not sure what type) and can't be ...
1
vote
2answers
87 views

Stable equilibrium in a gravitational field with 2 masses [closed]

Suppose you have two point masses $M_1, M_2$ in space and you locate the point $A$ on the line between them such that an object placed at $A$ is in equilibrium (the only forces acting on the obect are ...
0
votes
1answer
53 views

Why do forces/pressures/electrons/temperatures/etc equalize

What causes various forces/etc. like to equalize? I can understand water in a tank being affected by gravity but why do high pressure systems want to move to low pressure systems (vaccuums), electrons ...
0
votes
1answer
70 views

Boltzmann equation (Number density)

I'm trying to understand the Boltzmann equations use in the early Universe. The derivation is somewhat tedious, but in the end I end up with: $$a^{-3}\frac{d}{dt}\left(n_1a^3\right) = ...
0
votes
1answer
111 views

What is dynamic equilibrium actually?

Recently I have asked question sort of like that: Is thermodynamic equilibrium static or dynamic ? But then I wanted to realize what actually a dynamic equilibrium is. I read the wiki article, ...
0
votes
2answers
142 views

Thermodynamic equilibrium of an isolated system

When an arbitrary system is isolated and left to itself, its property will in general change in time. ....after a sufficiently long time,the temperature will become the same at all points and then ...
2
votes
2answers
97 views

Is Boltzmann distribution contradicting with the fundamental assumption of statistical thermodynamics?

In equilibrium statistical physics the fundamental assumption of statistical thermodynamics states that the occupation of any microstate is equally probable (i.e. $p_i=1/\Omega, S=-k_B\sum p_i\,{\rm ...
0
votes
2answers
505 views

Understanding mechanical equilibrium

In this site, mechanical equilibrium is defined as when there is no net force between the system and the boundary, it is in mechanical equilibrium. Now, what does it mean by net force? What would ...
1
vote
2answers
216 views

Is thermodynamic equilibrium static or dynamic?

Suppose, two parts of a system $A$ & $B$. They were at varying temperatures and hadn't achieved mechanical equilibrium. After the relaxation time, $A$ & $B$ were at thermal and mechanical ...
0
votes
1answer
133 views

Downward force applied at center of see saw [closed]

If we are given the length of a see saw of negligible weight, and the weights and distances from the center of the two people on the ends of the see saw, how can we find the downward force being ...