0
votes
0answers
152 views

Magnetic Fields and Surface Tension of Water

Here's a research paper exploring the effects of a magnetic field on the surface tension of water. http://iopscience.iop.org/article/10.1088/1742-6596/156/1/012028/meta The conclusions were that ...
2
votes
0answers
51 views

Why is the coefficient of kinetic friction greater than the coefficient of static friction? [duplicate]

I am a physics major taking freshman year physics courses. We did a lab experiment where we were given three objects and inclined plane, and we were asked to find the coefficients of kinetic and ...
-1
votes
1answer
73 views

2D Kinematics and Projectile Motion [closed]

In this page, I have finished most of the problems. Some of them I am unable to figure out. For 3 a-j, is it possible to solve this problem given parts a and b, that is, can I solve these problems ...
3
votes
1answer
104 views

How strong a magnetic field would be needed to deflect cosmic rays?

How strong a magnetic field would be needed to deflect cosmic rays? For example, lets imagine we wanted to protect the occupants of the International Space Station from cosmic rays. I assume we would ...
1
vote
3answers
199 views

$Q=mc\Delta t$ vs $Q=c\Delta t$

The thermal capacity of a $60 \;\mathrm{kg}$ human is $210 \;\mathrm{kJ/°C}$. How much heat is lost from a body if its temperature drops by $2\;\mathrm{ °C}$? My original working out was: ...
3
votes
0answers
90 views

Where this relation for general non rigid motion comes from?

In Goldstein's Classical Mechanics book in the chapter about the dynamics of rigid bodies the equation $$\dfrac{dL_i}{dt}+\epsilon_{ijk}\omega_jL_k = N_i$$ is presented. Now, in one exercise, we are ...
0
votes
2answers
64 views

Why wasn't the theory that light's velocity depended on its source very popular?

Before special relativity, it was believed that light having a specific velocity meant it had to travel through something. My question is, why wasn't the idea that light depended on its source very ...
1
vote
1answer
59 views

Moments question

The image is a body free-falling with two forces acting on it. If we take moments about A, we clearly get anticlockwise moments, and that is what will happen if this were to take place in real life. ...
2
votes
1answer
152 views

What does Addition of Angular Momenta tell us about Group Theory?

I've come across this a lot, but I've never understood it. I do know basic Group Theory including Lie Groups. In Introduction to Quantum Mechanics, Griffiths ends the chapter on spin with the remark ...
0
votes
0answers
48 views

A Lie derivative $\mathcal{L}_{\alpha^A}$ with respect to a spinor $\alpha^A$?

Suppose we work with Minkowski flat space $M$ (just to make things easy). If $\textbf X$ is a Killing vector field it is possible to define the Lie derivative of an spinor $\alpha^A$ with respect to ...
-1
votes
1answer
54 views

Graphing $E_p = E_k + E_{rot}$

I am measuring the moment of inertia of a flywheel and using conservation of energy to work out the value (I am ignoring friction). So for the experiment I have to roll the flywheel down a slope (I ...
1
vote
2answers
89 views

Does going downhill create cold air in the exhaust of a car?

Consider a car going down a large mountain. Instead of braking continuously, the driver shifts down and the car is able to maintain velocity on just engine braking. No fuel is injected into the ...
0
votes
0answers
59 views

Valence bands question

I'm currently doing solid state physics and learning about semiconductors. During the course, I have seen a lot of energy/wavevector graphs, like this one (pic from Kittel): I did not have a ...
1
vote
3answers
256 views

Can we predict throwing a dice?

What happens if we throw a dice from same position, with same force, by creating a vacuum environment on earth? Will it be predictable now i.e. will the dice have same results all the time? If answer ...
0
votes
0answers
19 views

Evaluation of width function; thermal neutron scattering cross section

I am attempting to perform some molecular dynamics simulation, based off of this paper, and do not have the slightest clue how they evaluate the width function (Eq. 4). My attempt at figuring it ...
0
votes
1answer
114 views

Single Slit Diffraction

I am trying to derive the intensity variation function for a single slit diffraction. Sorry for the poor diagram... So I decided to take the amplitudes of the waves originating from the slit on the ...
1
vote
1answer
152 views

What is the curve that describes the Daytime line in a Day and Night World Map?

A Day and Night World Map shows which parts of the Earth are in daylight and which are in night at a given instant. At one side of the Daytime line they are in daylight and at the other side they are ...
0
votes
0answers
51 views

Motion without matter

Suppose you have a vacuum spacetime with non zero cosmological constant then you can show that two test particles will move toward each other or apart depending on whether it is negative or positive ...
0
votes
0answers
52 views

How the malus law will be changed for the averaged intensity

If a polarized beam of light passes through an polarizer then, the intensity of the output polarized light obey Malus law. $$I =I_0 \cos^2 \phi$$ Now if we rotate the the polarizer with an ...
3
votes
1answer
62 views

Easy method to measure the NA of a lens system?

I have a lens system made up of some components of the Leica Z16 APO zoom system. This includes a built-in iris diaphragm to adjust the Numerical Aperture (NA) and therefore the depth-of-field (DOF). ...
3
votes
2answers
184 views

Multipole expansion in cylindrical coordinates

I am seeking the general solution for the Laplace equation in cylindrical coordinates or $$\nabla^2 \omega = 0. $$ In several texts, the general solution can be found via separation of variables ...
8
votes
3answers
2k views

Why are basic physics problems neglecting to include atmospheric pressure?

The value of atmospheric pressure is 101325 Pascal, which is a large value which implies the force exerted by atmosphere is 101325 N m$^{-2}$. Surely this can not be neglected, so why is atmospheric ...
2
votes
3answers
145 views

How did planets start to spin and do all of them spin in same direction? [duplicate]

How did planets start to spin in the first place? Some say that gases which condense and form planets start spinning and hence planets acquire a spin. And some say that they start to spin to conserve ...
-1
votes
1answer
162 views

Error propagation with dependent variables

Based on Microdosimetry theory, trying to figure out error propagation for a lot of quantities that are produced from radiation spectra where each channel with $f(y)$ counts has error $\sqrt{f(y)}$. ...
1
vote
1answer
68 views

Electric field vector in visualization of polarization of EM wave

When we were taught polarization at the high school level, we were told that during polarization, we should consider the EM wave being axially or planarly filtered (e.g. by a polarizing sheet with ...
3
votes
0answers
72 views

Why do they think WT1190F is low density?

A piece of space debris WT1190F is in the news in part because it has been far from earth (farther than lunar distance) in the past but will re-enter earth's atmosphere in a few weeks. See this note ...
0
votes
1answer
118 views

Relation of orbital radius with linear velocity of satellite [closed]

If a planet is going around the sun in a circular orbit , and if suddenly (impulsively) it's orbital radius was increased , what would happen to the linear velocity of planet (With reason)
-2
votes
1answer
90 views

Exothermic vs. endothermic reactions

An exothermic reaction is a chemical reaction that releases energy by light or heat. Does this mean that if I mix two chemicals in a test tube when the reaction between them is endothermic then the ...
0
votes
1answer
129 views

Why is it desired to have an aperture of a spherical mirror to be less than the radius of curvature?

In many instances, I have noticed that it is given that the aperture is less than the radius of curvature for a spherical mirror. Why is this given like that?
0
votes
1answer
62 views

Which waveguide mode will be excited by circularly polarized laser mode $\mathrm{TEM}_{00}$ entering hollow fiber?

Linearly polarized Gaussian mode $\mathrm{TEM}_{00}$ mode, would couple into HE modes of circular hollow fiber. Which modes would circular polarized beam excite entering hollow circular fiber ?
0
votes
3answers
94 views

Speed of electricity in cable [duplicate]

Movement speed of electricity in cable, is same as speed of light in space? In other words, electricity moves in usual electro cable aproximatelly 300 000 km/second ?
0
votes
1answer
330 views

What is the initial velocity of an object, given a change in mass, and an exerted force [closed]

An 8.0-g bullet is shot into a 4.0-kg block, at rest on a frictionless horizontal surface (see the figure). The bullet remains lodged in the block. The block moves into an ideal massless spring and ...
1
vote
1answer
88 views

Modeling transient heat transfer between two 1-D materials

So I have been working on creating a 1-D model of a material with a layer of heat resistant material stuck to it. For this I have been trying to use the implicit finite-differential method. The ...
0
votes
0answers
162 views

Alternative expression for Bethe vectors of su(2) XXX chain

As is well known, the eigenvectors of the transfer matrix for the su(2) XXX spin chain of length $L$ are given by acting on the ground state $|\uparrow^L\rangle$ with all spins point up with the ...
5
votes
3answers
493 views

Why don't surfboards fly out the back of a utility truck when driving on the highway?

I have never had it happen myself and every time I throw my boards (shortboards not malibus) in the back of someone's ute, with no cover on the tray, they always assure me they'll be alright( the ...
0
votes
1answer
46 views

Avoiding a singularity in the simulation of a spherica pendulum

I didn't know whether to put this here or in StackOverflow - so I open to answers just telling me to go there! I am looking to simulate the motion of a spherical pendulum. The Lagrangian is $$ ...
4
votes
2answers
212 views

Why is $d^4p$ “obviously” Lorentz invariant?

Is there a mathematical and a physical reason? I believe it follows from the jacobian of the Lorentz transformation. But, if that is so, I don't see why it would be "obvious" unless you can do such ...
11
votes
1answer
272 views

Why is the second law of thermodynamics indisputable? [duplicate]

Why is the second law of thermodynamics undisputable? On his website Professor Hawking says the following: The cosmologist, Sir Arthur Eddington, once said, 'Don't worry if your theory doesn't ...
0
votes
2answers
58 views

Defining charateristic of light wave?

"Light is refracted when it travels from one medium to another." Does the sentence show that light is a wave?
4
votes
0answers
74 views

${\phi}^4$ description of Ising ferromagnet

Suppose the coupling between two spins is $C_{i,j}<0$, then the classical partition function is given by $$Z=\sum_{\{s_i\}}e^{\sum_{i,j}s_iK_{ij}s_j+h\sum_{i}s_i}$$ where $K_{ij}=-\beta C_{ij}$ and ...
0
votes
2answers
264 views

Magnetic flux density of a solenoidal electromagnet

I am designing an electromagnet which will be used to test magnetic sensors. So I used to formula found at hyperphysics which relates the magnetic field flux density to the number of turns, the ...
1
vote
0answers
125 views

Mass, density and gravity for 2D SPH

Having previously only worked with 3D sph, the 2d case is confusing me. The concept of mass and density as well as gravity is not easily converted, as I see it. As an example in 3D I take 1000 ...
0
votes
3answers
278 views

Friction of a rolling cylinder

I was wondering why friction vectors are drawn differently regarding a cylinder rolling on a surface and a cylinder rolling down an inclined surface. Since friction is responsible for the rotational ...
4
votes
3answers
577 views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
1
vote
2answers
62 views
0
votes
1answer
66 views

Will the heat flow rate be same when temperature difference is not same?

If I give heat with a certain source will the change of temperature difference change the heat flow rate? Suppose I have a aluminium rod which has a weight of 25 gram. I heated it up to 40 degree ...
0
votes
0answers
51 views

How do chirped mirrors compensate dispersion?

How do chirped mirrors compensate dispersion? I understand that if you have longer wavelengths penetrating deeper into a chirped Bragg stack, then there will be some anomalous dispersion because the ...
0
votes
2answers
162 views

What happens to the kinetic energy of a system in a non-elastic collision? [duplicate]

I know that the kinetic energy of a system is NOT conserved in a non-elastic collision. But energy is supposed to be conserved, so where does all that energy go? Is it transformed into other forms ...
1
vote
1answer
116 views

Switch from the position representation to the momentum representation

If we use Fourier Transform, we can switch from the position representation to the momentum representation, like the following formula here comes the problem, if we use dirac notation we can see it ...
1
vote
2answers
117 views

What's the right way to calculate power consumption over a month given a rate per minute?

When I was searching for power required to lift an object, i found that, for example: $100\ \mathrm{kg}$ to be lifted 3 metres in 5 seconds. (vertical) Answer: $$\begin{align} ...

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