3
votes
1answer
424 views

Why are lab Magnets painted red?

Wy are lab magnets painted red in color? I tried searching everywhere but couldn't get a satisfactory answer.
1
vote
1answer
945 views

Confusion about the probability cloud

What is the meaning of the electron probability cloud? I understood it to mean that the electron has a probability to be found in a certain postion before measurement, but now after reading ...
8
votes
2answers
372 views

Does Hamilton Mechanics give a general phase-space conserving flux?

Hamiltonian dynamics fulfil the Liouville's theorem, which means that one can imagine the flux of a phase space volume under a Hamiltonian theory like the flux of an ideal fluid, which doesn't change ...
6
votes
1answer
307 views

Trajectories of particles with spin in Einstein-Cartan theory

The Einstein-Cartan theory is a generalisation of General Relativity insofar as the condition that the metric affine connection is torsion-free is dropped. In other words, the space time is a ...
-1
votes
1answer
129 views

Electrical circuits problem

Batteries have a circuit which looks like this : The electrons go around the circuit and then return through the battery where they get charged again and flow around. My issue is, what about ...
7
votes
1answer
1k views

What is the precise statement of the OZI Rule?

What is the precise statement of the OZI Rule? I've heard that a diagram is OZI suppressed if it can be "cut in two by cutting only gluon lines", but I don't really understand. For example, consider ...
-1
votes
2answers
2k views

Do water movement in the seashore represent waves? [closed]

I have seen water moving front and going back in the seashore.Do they represent waves?Explain.
9
votes
4answers
1k views

D'Alembert's Principle: Necesssity of virtual displacements

Why is the D'Alembert's Principle $$\sum_{i} ( {F}_{i} - m_i \bf{a}_i )\cdot \delta \bf r_i = 0$$ stated in terms of "virtual" displacements instead of actual displacements? Why is it so necessary ...
0
votes
0answers
38 views

Magnetic field distrotion

Does one exist, or do you think it would be possible to design a tracking magnetic field distortion detector to detect fast moving magnetic anomalies in our air space. ie; track a stealth aircraft or ...
-1
votes
2answers
141 views

Elementary physics question…requires calculus?

A 2500.0kg car is going at a constant velocity of 14.0 m/s and hits the breaks to stop. It skids 25m. What is the coefficient of friction of the tires to the ground? So I have acceleration = -4.0 m/...
-1
votes
1answer
361 views

Does a black hole have an interior or does the spacetime manifold itself end at the event horizon? [closed]

There have been a number of intriguing ideas over the years hinting at the possibility that a black hole might not have an inside, that it might consist of nothing but a surface and an external ...
1
vote
2answers
183 views

Sign in the time-independent Schrödinger's equation

In the time-independent Schrödinger's equation: $$ -\frac{\hbar^2}{2m} \frac{d^2} {dx^2} u + Vu ~= Eu, $$ why there is a minus sign before the first term?
1
vote
1answer
107 views

Variance and Intermittency in turbulence

In the turbulent transport of a scalar field, $\Phi$, decomposed into mean and fluctuating components, $\Phi=\left<\Phi\right>+\phi^\prime$, the scalar variance is defined as $\left<{\phi^\...
1
vote
4answers
252 views

Defining simultaneity with a central light vs with clocks

So there's the classic example of the relativity of simultaneity involving two people on a train, with a light source exactly between them. Moments after the lights turn on, observers on the train ...
-1
votes
2answers
758 views

What does “along the handle of the cart” mean? And how does one calculate weight?

A horizontal force is used to pull a $5.0\text{ kg}$ cart at a constant speed of $5.0\text{ m/s}$ across the floor. The force of friction between the cart and the floor is $10\text{ N}$. What ...
4
votes
1answer
98 views

How to derive the Mott gap mathematically

From the one-band Hubbard model, $H=-t\sum\limits_{<ij>, \sigma}c_{i\sigma}^{\dagger}c_{j\sigma}+U\sum\limits_{i}n_{i\uparrow}n_{i\downarrow}$, we know if $U\gg t$, the energy cost of two ...
4
votes
0answers
289 views

Time Reversal in Euclidean Spacetime - unitary or antiunitary?

(pre-request) We know that time reversal operator $T$ is an anti-unitary operator in Minkowsi Spacetime. i.e. $$ T z=z^*T $$ where the complex number $z$ becomes its complex conjugate. See, for ...
1
vote
1answer
158 views

How does enthalpy help us to find the state of equilibrium?

For an adiabatic system with constant external (generalized) forces, in a state out of equilibrium we have: $$\delta H\leq 0 $$ If I understand correctly, derivation of this inequality does not rely ...
1
vote
1answer
74 views

How can enzyme/substrate reactions that adhere (largely) to quantum theory also require 'Newtonian' consideration of gravity?

I'd just like to ask for a little clarification here due to confusion from interdisciplinary studies. I'm currently reading the 1976 paper related to the recent 2013 Nobel Prize for Chemistry, by 2 ...
4
votes
4answers
12k views

Are reversible adiabatic processes always isentropic?

If my understanding is correct, neither reversible nor adiabatic processes are necessarily isentropic. But are reversible adiabatic processes always isentropic?
2
votes
1answer
243 views

Virtual particles and S-matrix

One of methods of introducing of virtual particles is using perturbation theory. We say that scattering matrice amplitude $M_{in \to out}$ contains of $\delta(P_{out} - P_{in})$, which realizes energy-...
4
votes
3answers
1k views

How can a block which is not receiving the direct force have a greater acceleration?

I solved it like this: $$F(\text{st max})=5\text{ N}$$ For the top block, $$\begin{align} 6\text{ N} - 5\text{ N} &= 1a \\ a &= 1\ \mathrm{m/s^2} \end{align}$$ For the lower block, the ...
0
votes
3answers
458 views

Expansion of the Universe: Conversion of gravitational potential energy to kinetic energy?

Suppose there is an object floating in space which over time begins to fall toward the source of a gravitational field. As it falls, its motion happens to be such that it gets locked in orbit around ...
0
votes
0answers
157 views

Energy required to demagnetize a soft iron?

How much energy is required to demagnetize a soft iron ferromagnetic material, that has a very low coercive force And a small hysteresis area? Also, would it be possible to demagnetize that same ...
1
vote
1answer
101 views

Perihelion Advance in curve space

I've been doing some work that involves particle's motion subjected to central forces. I was trying to compute the perihelion advance of the particle's path. For that I've been following this ...
3
votes
1answer
589 views

Understanding heat pump efficiency

I have read that heat pumps are more efficient than generating heat directly for heating homes, until the temperature gets down to a critical value. I just asked how to calculate temperature of ...
1
vote
2answers
840 views

Water doesn't flow above the rim, one reason is surface tension. Is another reason viscosity?

According to Surface tension, water molecule don't get the force from outside and get little bit outward. Is one reason viscosity? Let's look at the water in a fully filled glass. No part is outside ...
2
votes
0answers
214 views

N-body forces in classical mechanics

For a system of two interacting particles 1, 2 we get from the conservation of momentum $$ \dot{\bf{p_1}} + \dot{\bf{p_2}} = 0$$ ...
0
votes
1answer
322 views

Find current in a nontrivial circuit

Let us assume that we have this circuit: We know that: $$I_1 = I_2 + I_3$$ $$I_1R_1 + I_3R_3 = V$$ $$I_1R_1 + I_2R_2 + \dfrac{q_c}{C_1} = V$$ Therefore we can write: $$I_1 = k_1 - k_2*q_c$$ ...
-5
votes
6answers
3k views

Why won't protons revolve around the nucleus containing electrons and neutrons?

In case of solar system,we can explain "Why Sun would not revolve around any other planet?",by giving the reason that Sun is heavier than any other planets. Heavier the body,greater will be the ...
3
votes
2answers
990 views

Measuring Cryogenic Temperatures

I need an inexpensive instrument to measure cryogenic temperatures (down to -200C). I can build a thermistor-based thermometer using an Arduino that is accurate to under 1 degree for 0 to 100C. ...
1
vote
0answers
358 views

How to measure the energy required to pedal an exercise bike

I have hacked a FitDesk exercise bike to output the RPM of the pedals and the position of the resistance control within its range of travel. I want to characterize the energy that is required to ...
1
vote
3answers
123 views

Behavior of gasses, ideal and otherwise

I'm trying to help a child research a science project on refrigeration. Refreshing my incredibly rusty thermodynamics skills.... The ideal gas law: $PV=nRT$. Let's take air at STP: $P = 101\,kPa$ $V ...
8
votes
1answer
693 views

What is the reason of the semidiurnal pressure oscillation in the atmosphere?

It appears that in many (most) places on earth, a pressure oscillation of a 100-200 Pa takes place twice a day : that is, with maxima around 12AM and 12PM and minima around 6AM and 6PM. I've found ...
9
votes
4answers
3k views

Why is the Copenhagen interpretation of quantum physics the most widely accepted one?

I've been digging a lot into quantum physics in the last few weeks. I didn't care much about the maths, just about what empirically happens to get a conceptual idea about quantum phenomena. The most ...
7
votes
2answers
413 views

Time dilation only on electromagnetic force?

We've seen by experiment that the speed of light c appears to be constant for each observer (leading to all well-known consequences of relativity). I'm wondering if this appearance of constancy of c ...
-3
votes
1answer
124 views

What is the speed photons coming out from headlights of a car running 100 km/h? [duplicate]

And, technically, would the color of the light change at different car speeds?
-2
votes
3answers
239 views

Why heavier bodies produce greater gravitational pull than the lighter bodies?

The basic question "Why planets revolve around the Sun?", is explained by taking into account the heaviness of Sun. The lighter bodies are considered to move around heavier bodies,as like lighter ...
0
votes
1answer
67 views

In what range the acceleration value of quantum particle lies?

According to Heisenberg's uncertainity principle, the position and velocity of an quantum particle cannot be determined simultaneously. Is it possible to determine position and acceleration ...
7
votes
1answer
383 views

Magnetic field lines and knots

As I was reading the book The Trouble With Physics, I encountered a small paragraph which seemed bit confusing. The paragraph goes as follows: Picture field lines, like the lines of magnetic field ...
0
votes
2answers
72 views

Electron motion in a wire

For my introductory course to electromagnetism (I'm an undergraduate student, so ELI5), I'm trying to get the right conceptual model of electron movement in a thin wire (with constant but non-zero ...
0
votes
1answer
127 views

why does water do that?

I found recently that water fills a bottle quicker through only observation if I hold the tube away from the filling water than if I leave the tube inside the bottle. why does that happen? does ...
1
vote
3answers
7k views

Generator using Earths's Magnetic field?

In the past I've been shown Internet sources claiming a specific generator that uses nothing but the earth's magnetic field to generate power, I'm looking for the name of the generator? I realize ...
2
votes
3answers
86 views

Measurements from inside conductors

We have known for some time now that when electric field is applied across any conducting shell, then electric field inside it would be zero. It also has some fantastic applications such as ...
0
votes
1answer
378 views

Does the Casimir effect give the correct value for Dark Energy?

My understanding is that the Casimir Effect is caused by vacuum energy. Quantum mechanics (QED) predicts vacuum energy, but gets the value grossly wrong, by a factor of $10^{120}$. On the other hand, ...
5
votes
1answer
1k views

Can we model Chemical Reactions using Quantum Mechanics? If so, what is the most complex reaction we can model?

Not a physicist or Chemist, just interested in QM and it's applications. I've been reading lately about Quantum Chemistry and it occurred to me that since we can model electron orbitals in QM and ...
8
votes
2answers
251 views

Do siphons really require air pressure to function?

Can the siphon mechanism work in vacuums? There seems to have been experiments where exotic liquids (low vapor pressure) were used in siphons mounted in vacuum chambers. The idea is that the falling ...
3
votes
2answers
534 views

Strong Newton's third law of action and reaction: Mathematical Interpretation

According to the strong law of action and reaction for internal forces(Goldstein): "$F_{ij}=-F_{ji}$ and the forces lie along the direction joining the particles." Now consider the statement If ...
13
votes
6answers
23k views

What are the fields produced around a current carrying conductor?

If you consider a current carrying conductor, every instant an electron enters the conductor, another electron will be leaving the conductor. Thus, the current carrying conductor will not be charged (...
17
votes
2answers
195 views

Is there an official name for “Lorentz Pairs” like energy and momentum?

In learning about relativity I've noticed that in the construction of Lorentz invariants (specifically four-vectors) two physical quantities that were previously considered distinct are instead ...

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