# All Questions

513 views

### Momentum (apparently) not conserved in one of my class' experiments

I am a TA for an introductory mechanics course. We performed an experiment yesterday examining two-dimensional collisions. One of the things we hoped to show in the course of this experiment is that ...
164 views

### Basic question about Magnetism and Right hand rule? [closed]

In our physics class we had a brief introduction to magnetism - the very basics, but I don't understand the right hand grip rule. Here is the question I'm stuck on: "a negatively charged object ...
28 views

### How can a cable pass signal

I am currently study electrostatics. And I don't get how can electrons pass signals in a cable, can somebody explain this to me specifically?(I am only twelve years old) Thank you very much!
68 views

### What is the Kerr factor for Sagittarius A*?

I have searched for it, but everything what I found is that A0620-00 (the current closest black-hole to Earth) is a slow spinner with Kerr factor $a=0.12$. How about the Kerr factor for Sagittarius ...
15 views

### Galerkin-type weak formulation for electrokinetics

I am currently working on finite element simulations about electrokinetics. My solver (getdp) accepts directly galerkin-type weak formulation of equations. I am thus trying to write my equations in ...
3k views

### Why is the sky of the moon always dark?

Why is the sky of the moon always dark compared to the sky of the earth, doesn't it have day and night like earth?
125 views

### Electromagnetic braking hypothetical situation?

Let's say there is a conducting rod in space - with a constant external magnetic field. If you spin the rod - will electromagnetic braking make the rod stop eventually? I feel like there is a change ...
26 views

### What is the physical basis behind burnt calories estimates?

we see on treadmills, bikes, fitness trackers, etc., estimations of calories burnt. These are clearly based on correlations to weight, age, hear rate. How were these values correlated? Is there a ...
24 views

### Can single maximal fraction be increased by one-party local operation?

For a quantum channel $\Lambda$, the corresponding bipartite state is $\rho=(I\otimes\Lambda)(|\Phi\rangle\langle\Phi|)$, where $|\Phi\rangle=\frac{1}{\sqrt{n}}\sum_{i}|ii\rangle$. The maximal ...
40 views

### On the definition of the compressibility`

The compressibility factor for a real gas can be defined in two equivalent ways, $$Z = \frac{V_{measured}}{V_{ideal}} \equiv \frac{p_mV_m}{nRT}$$ where the subscripts $m$ stand for measured ...
117 views

229 views

### Where do sound waves go after being heard?

I honestly can't come up with anything that makes sense, because obviously, energy cannot be created nor destroyed. I think the question is pretty self-explanatory, so there isn't much to say here.
46 views

### Background gamma radiation

There are plenty of lists of sources of general background radiation, but can anyone reduce that list to the major contributing sources purely for background gamma radiation (specifically low energy, ...
40 views

### Error in radius squared

I am performing an experiment to determine the ratio e/m using a Helmholtz coil. I am using a chi squared minimization routine to find e/m. The data is supposed to fit, $$r^2=kV$$ Where k is ...
100 views

### Biot-Savart Law Clarification

I have a question concerning Biot-Savart's law. It pertains to problems where you must find the total magnetic field at some point P, $x$ meters away from a current-carrying wire. I am a bit confused, ...
112 views

### Newtons 3rd law, on two opposing discs?

Assume a large disc at rest(bottom disc), and free to move. Above it is another disc(disc2) that's rotating, and a motor fixed on that large disc(bottom disc) as well, that's load is a disc rotating ...
99 views

### How to solve Kinematics: two objects meeting in the air

A water balloon is dropped from the top of a 200m high tower. An alert archer at the base of the tower sees the balloon being dropped, waits for 5s, then shoots an arrow at 40m/s straight up towards ...
128 views

### Circular motion and momentum

I have to explain why there is a force pointing inwards in a circular trajectory (assume constant speed), but without relying on centripetal force argument. Coordinate system is Cartesian ...
40 views

### Trying to understand electron diffraction

I'm trying to understand how electron diffraction works, but I'm not really getting it. Here's an image Here are a couple of questions about it that I can't figure out. Why is the angle of the ...
110 views

### Identify for $f(\infty)+f(-\infty)$ in quantum field theory [duplicate]

In Matthew Schwartz's textbook, Quantum Field Theory and the Standard Model, equation 14.68 on page 266 says the following: ...
61 views

### In which direction along a GaN (wurtzite) crystal are only Ga atoms being observed?

So, if you have an electron microscope image of a GaN crystal, and that it shows only white dots which represent Ga atoms. No nitrogen atoms are seen in the image. Along which direction is this ...
96 views

### Model for temperature and pressure inside a heated vessel with liquid being pumped into it

I am working on a problem where a pressure vessel is pressurized by heating the vessel to a high temperature and then injecting a liquid into the vessel that boils and hence increases the pressure in ...
76 views

### What is the difference between these two equation dealing with time dilation?

In my textbook, the time dilation equation is presented as $\Delta t' = \gamma \Delta t,$ where $\gamma = 1/ \sqrt{1 - v^2/c^2}$. My understanding of this equation is as follows (correct me if I'm ...
12 views

### How 2nd-order nonlinear optic response is used in the telecom market?

References According to this paper, 2nd order NLO response is important for telecom. According to Wikipedia, Lithium niobate is used extensively in the telecoms market, e.g. in mobile telephones ...
195 views

### Physics without time

The structure of physical law as we generally recognize it today is firmly held together by the existence of time. Although physical laws can both predict and retrodict (reversible time does not break ...
57 views

### Can Theta be greater than 360 degrees in this equation?

I have a quick question regarding Rotational Motion. I understand the equation x = r (theta) and I know that theta represents the Angular Displacement for a circle but what if the linear distance ...
43 views

### Does a time-varying intensity contribute to the photoelectric effect?

I understand the photoelectric effect demonstrates that electrons are only dislodged from a metal if incident light meets a minimum threshold frequency. I wonder if a varying intensity might also ...
110 views

### How do particles in a wave make the next particles move?

i only know few things about waves,but this question just popped up in my mind. I already know that the particles transfer energy to each other,but i do not know HOW they do it! The truth is that i ...
26 views

### Temperature Frequency relationship for gas?

I am getting something like this T (C) = Constant*log(Frequency) I do not have background of physics and I am wondering, if there is any formula which can explain the physics behind it? Something ...
53 views

### Photon propagator inverse

If i have the operator $D^{\mu\nu}=\partial^{\mu}\partial^{\nu}+m\epsilon^{\mu\alpha\nu}\partial_{\alpha}$. What's your inverse $(D^{\mu\nu})^{-1}$?
35 views

### Solitons and its infinite extension

A soliton, for example the KdV equation solution, has the profile proportional to a hyperbolic secant squared ${\text{sech}}^{2}(x-ct)$. And since it is hyperbolic it has an exponential dependence, so ...
28 views

### Translational versus dilatational zero modes?

Why are the zero modes of the SU(2) Yang Mills instanton referred to as translational or dilatational zero modes? Is this standard terminology?
33 views

### How is ink's color produced?

From https://en.wikipedia.org/wiki/Complementary_colors The pairs of complementary colors vary depending upon whether the colors are physical (e.g. from pigments), or from light. These change ...
74 views

### can a really loud sound travel in space?

I heard in a discovery news video that there is one particle every cubic cm in space. So, if i were to vibrate a circularbody of say mass 10000000kg at 10000000000000000000000Khz, would i be able to ...
62 views

### Why does magnetic flux linkage become negative when a coil is turned through 180degrees?

Taking a rectangular coil, in a constant magnetic field, it is understandable that BANcos(theta) should apply for the magnitude of the flux linkage. However if the coil is turned through 180 degrees ...
23 views

### Time for water wave to reflect

In class we discussed an experiment for measuring the speed of waves in water. The basic procedure went something like this: Make a wave at the near end of the tank and wait for it to travel to the ...
I would like to determine the general expansion of $(A+B)^n$, where $[A,B]\neq0$, i.e. A and B are two generally no-commutative operators. How could I express this in terms of summations of the ...