0
votes
0answers
1 views

Importance of Powers of Velocity in Classical Mechanics

This is an incredibly naive question, but I am curious enough to ask anyways. Is there any general significance to calculated quantities that depend purely on general powers of the velocity of a ...
0
votes
0answers
2 views

Conductors and Uniqueness Theorem

I'm working with Griffiths Electrodynamics, and he introduces a uniqueness theorem: First Uniqueness Theorem: The potential $V$ in a volume $\Omega$ is uniquely determined if (a) the charge density ...
3
votes
7answers
1k views

Degree of freedom paradox for a rigid body

Suppose we consider a rigid body, which has $N$ particles. Then the number of degrees of freedom is $3N - (\mbox{# of constraints})$. As the distance between any two points in a rigid body is fixed, ...
0
votes
0answers
8 views

Can a string be so thin it's invisible, but still support a visible weight?

A spider web thread is very thin, yet it can support a spider. Given that the human eye visual acuity is finite, are there materials, natural or man-made, sufficiently thin that a string made from ...
0
votes
0answers
4 views

Fill and drain tank (same time) [on hold]

Consider an open tank with cross section area A, into which liquid can enter at the top through one pipe and leave at the base through another. If the liquid enters at the constant rate of a volume of ...
0
votes
1answer
9 views

How To Calculate A Meteor Impact

Exalted Physics Gods of the Internet. I am trying to add a dose of realism to a story I'm writing. Long story short: Basically imagine an invulnerable superman-like being that won't disintegrate at ...
0
votes
1answer
43 views

Quadratic versus other types of degrees of freedom

In my text book I have the following question and after thinking about this one for hours, I can't figure out what they're getting at: In Section 2.5* I quoted a theorem on the multiplicity of any ...
1
vote
2answers
38 views

How does electrostatic force affect electronic devices?

How does electrostatic force generated by two seperate plates having opposite charges affect electronic devices? I know that magnetic fields have some harmful effects to electronic devices but I am ...
0
votes
1answer
18 views

Question on the negativity of the coefficient of restitution

I was trying to solve a Mechanics question on Momentum. Here is the question : Two small smooth spheres A and B have equal radii and have masses m and km respectively. They are moving in a ...
0
votes
2answers
189 views

On deriving the Schrödinger Equation

I do know that one can't actually derive any axiom, but here is my serious attempt to explain the Time Independent Schrödinger Equation with minimum preliminary knowledge. In the following $f$ is ...
8
votes
3answers
1k views

Is it possible to have rate of change of acceleration?

I know this may seem a weird question, but it always bothers me. My physics book (Resnick,Halliday,Walker), and also various sites never say anything beyond acceleration. But when a moving body is ...
0
votes
2answers
115 views

Dielectric constant of water

I need the dielectric constant of water from $10^{-2}$ Hz to $10^4$ Hz. As stupid as it may seem, I cannot find much info. I've googled for days. All I can find is close to GHz. And the only info ...
1
vote
1answer
37 views

Mapping Issues with Unbounded Operators

Consider the operator-valued generalized function $\phi^{(k)}_{l}:=\phi^{(k)}_{l}$ on space-time $\mathcal{M}$. Now, smooth the operator-valued generalized function with test function $f(x)$ ...
3
votes
1answer
274 views

Homopolar motor and Lorentz force

My second grader thought making a homopolar motor for her science experiment would be fun. And, it was. Now I am trying to explain how it works and the Lorentz force. Please help me by giving me a ...
0
votes
0answers
6 views

Final temperature of an air parcel

How would one find the final temperature of an air parcel ascending adiabatically in the atmosphere? Like which formula would you use? I used the equation of state for dry air to find the initial ...
0
votes
1answer
11 views

Using Maximum Principle to see conductor is equipotential

This is a problem from electrostatics, but I'm trying to understand it in terms of harmonic functions. Let $B\subset\mathbb{R^3}$ be a conductor. It can be shown that the electric potential ...
0
votes
0answers
12 views

Calculation of the partition function for a classical 2D gas lying on the surface of a sphere of constant radius $R$

I'm kind of confused with this system. My first question is. Is the Hamiltonian of one particle of this gas the following? ...
2
votes
1answer
14 views

Dry adiabatic lifting

If an unsaturated air parcel ascends adiabatically in the atmosphere with an initial temperature, would the final temperature of the air parcel, when it reaches it's destination, be the same at the ...
0
votes
1answer
68 views

Is the plane wave model always valid in reflection and transmission?

my question is related to another one I asked, but I foolishly made that question about several things (experiment, computation, theory) at once so it was confused. I was talking to my boss about ...
4
votes
1answer
29 views

Energy usage in different reference frames

Imagine a moving object at constant speed (like a car). This object is, then, accelerated for a brief moment. In different reference frames (at rest and moving along with the object), the variation of ...
0
votes
0answers
23 views

HW Question: Force of a Car on a Truck

Here is another homework question that is confusing me... A 1000 kg car pushes a 2000 kg truck that has a dead battery. When the driver steps on the accelerator, the drive wheels of the car push ...
2
votes
4answers
90 views

Application of Kirchhoff's laws in circuits with inductors

As we know,the Kirchhoff circuit laws are applicable for conservative electric fields. Now it is applicable for circuits where inductors are present but the field there is not conservative. So how ...
0
votes
1answer
21 views

why is the focal length of a convex mirror negative?

According to the Cartesian sign convention, the focal length should be positive since the convex mirror forms a virtual image to the right of mirror (positive direction) when light comes from left. ...
0
votes
0answers
15 views

Maximum friction force for a wheel to be able to roll

The wheel with mass $M$ and radius $R$ below is free in space (it is not on the ground). A torque $\tau$ is applied to it through an engine. A horizontal force $F = \frac{\tau}{R}$ is also applied to ...
1
vote
1answer
31 views

Indicate if objects after collision will stick

Is it possible to indicate if objects after collision will stick together knowing their properties(materials,hardness,etc)?
0
votes
0answers
14 views

Why is the law of the junction valid under forward bias?

I'm currently studying the physics of the PN junction. I went though the derivation of the built-in potential in the PN junction under equilibrium: $$ {Diffusion\ current\ density} = {Drift\ current\ ...
0
votes
1answer
37 views

How does electric field intensity look like along a wire which has one end connected to an AC source and the other one is left free?

How does the electric field intensity look like along a wire with constant conductivity which has one end connected to an AC source and the other one is left free? I mean is the electric field the ...
2
votes
1answer
34 views

If hot air expands in all directions why is the balloon moving up?

A balloon is moving up. The hot air inside the balloon is expanding in all directions and cold air outside the balloon acts with force on the balloon from all directions (higher pressure force). Why ...
15
votes
5answers
658 views

Conservation of Mathematical Constraints when deriving Energy and Momentum from $F=ma$

Background: Starting from $F = ma$, integrating with respect to time, and using basic calc, one can derive $\int Fdt = m (v_f - v_i)$ Starting from $F = ma$, integrating with respect to distance, ...
0
votes
1answer
80 views

Do reversible processes exist in Nature?

Classical thermodynamics always discusses entropy in the light of reversible processes, and it lies at the heart of the definition of entropy. But do these reversible processes exist in Nature, or are ...
0
votes
0answers
15 views

How does ground interact with a box rotating around its corner?

I have some questions about how forces $F$, friction force $F_{friction}$, and normal $N$ interact in order to the box below to turn (clockwise) about the red corner, without sliding. The force $F$ is ...
0
votes
2answers
48 views

Thermodynamic reversible process

My book says "A process is said to be reversible if it is carried out infinitesimally slowly so that in each step thermodynamic equilibrium of the system remains unchanged & any infinitesimal ...
0
votes
1answer
68 views

How to calculate the supporting force exerted by a stationary object (cupboard) and support (brackets) for it?

I have a wall mounted Stuva Ikea cupboard, which measures 60x64x30cm. The base is 64x30cm. It is already supported by 2 holes at the back base, (64x60cm). But I need to add in L shape brackets ...
0
votes
1answer
41 views

Special relativity; spaceship moving towards a planet

A spacecraft starts travelling from Earth, moving at constant speed, towards a yet-to-be-discovered planet, which is $20$ light hours away from Earth. It takes $25$ hours (according to an ...
0
votes
2answers
24 views

calculating emf with and without resistance

A battery of internal resistance 2 Ohms is connected to an external resistance of 10 ohms. The current is .5 A. What is the emf of the battery? The correct answer is 6.0 V. When I calculated it like ...
0
votes
0answers
38 views

Projection Method in Hubbard model

This is a question from Altland and Simons book "Condensed Matter Field Theory". In the second exercise on page 64, the book claims that if we define $\hat P_s, \hat P_d$ to be the operators that ...
3
votes
1answer
39 views

Curvature of electrostatic potential is zero

Could you please expound upon this claim? I found such claim on Zangwill's Classical Electrodynamics, which states that constraint coming from Laplacian equation implies electrostatic potential has ...
1
vote
1answer
89 views

Atomic nearest neighbor notation

I recently got a correction to a paper that I am writing. The correction references a section in which I talk about nearest neighbors. The comment says: Do you mean NN, NNN, etc., or NN, 2NN, 3NN? ...
31
votes
5answers
3k views

How is it possible to accelerate a neutron?

It is possible to accelerate a charged particle in an electric field, how is it possible to accelerate a neutron? How can we control its velocity?
4
votes
6answers
580 views

When has the speed of light been measured, recently?

Yes, it is weird, absurd, but I can't stop thinking that the would-be superluminal neutrino speed has been computed by an arithmetic operation (space/time) and not by direct comparison with a ...
0
votes
0answers
26 views

How many exobiologist are there in the world? How many exobiologists are there who work specifically on the search for extraterrestrial intelligence? [on hold]

I have two questions: How many exobiologist are there in the entire world? How many exobiologists are there who work specifically on the search for extraterrestrial intelligence? (I emphasize the ...
3
votes
1answer
63 views

Experiment which shows that Newtons third law is not true for magnetic forces

I am just reading David Morins "Introduction to Classical Mechanics". He writes about Newtons third law the following: It holds for forces of the “pushing” and “pulling” type, but it fails for ...
1
vote
3answers
79 views

What is special about the ratio $Q/V$ that we give it the name Capacitance?

Why is the ratio Charge/Potential important? Also, usually when we add charge, the potential changes. Then why do we care how much charge we can put on a conductor for a given potential.
0
votes
0answers
28 views

Cable being pulled at more than two points with a load at one end

Pulling a cable through a series of pulleys with a linear actuator Point A- where actuator attaches at the end of the cable (actuator rated at 2001 Newtons of force) Point B- Will also be pulled by ...
1
vote
1answer
52 views

Gauge pressure clarification

Is gauge pressure always zero-referenced against ambient air pressure? Or is it referenced against the sum of all pressures acting on a fluid, which usually just happens to be ambient air pressure? ...
6
votes
0answers
51 views

Why Lorentz group for fields and Poincaré group for particles?

Wigner treatment associates to particles the irreps of the universal covering of the Poincaré group $$\mathbb{R}(1,3)\rtimes SL(2,\mathbb{C}).$$ Why don't we consider finite dimensional ...
11
votes
2answers
426 views

How is graphene a 2D substance?

How is graphene a 2D substance? It has length, width and some thickness to it, else it would be invisible. Why is it considered a 2D substance?
0
votes
0answers
16 views

Beta plus decay [duplicate]

I think I understand beta minus decay: A nucleon loses mass and this mass is converted into an electron and an electron anti-neutrino. Correct? (I imagine there might be some kinetic energy too but ...
0
votes
0answers
17 views

Projection of a Moment (Torque) about an axis

What is the difference between the projection of a moment, about a point $O$ on an axis $l$, along that axis $l$ vs. the projection of a moment, about a point $D$ not on that axis $l$, along that ...
1
vote
1answer
49 views

Non-discoveries by the Kepler space telescope: exomoons, co-orbital planets, trojans

I am just reading the review article Advances in exoplanet science from Kepler (arxiv preprint: http://arxiv.org/abs/1409.1595), and I found a remarkable paragraph (last paragraph in section ...

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