General Q&A about physics of any type and at any level
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These WorldFamous companies advertise that their lenses can control myopia for kids, NOT adults. But none of these lenses are approved by FDA. I asked my optometrist why merely kids, not adults. Bu...
The Rayleigh-Jeans law does a good job of describing the spectral radiance of a black body at low frequencies: $$B_{\nu}(T)=\frac{2kT\nu^2}{c^2}$$ with $T$ the temperature and $\nu$ the frequency...
How to derive the Lagrangian differential force? $$\frac{d}{dt}(\frac{\partial L}{\partial \dot{x}})+\frac{\partial L}{\partial x}=0$$ I was trying to do something. $$L=T-U=\frac{1}{2} m\dot{x}^...
If we have a force which changes depending on the position of a particle, how can we find the position of the particle at some time $t$? We can find its velocity if it has travelled a given distan...
Which one is correct? $$E=mc^2$$ or $$E^2=(mc^2)^2+(pc)^2$$ I mostly seen $$E=mc^2$$ from my childhood, and when I was learning problem solving in relativistic mechanics I had seen $$E^2=(mc^2)^2...
I stumbled these pictures on Quora, and I'm assuming they were real. Wouldn't the supporter (person whom gun is mounted on) suffer hearing loss? Wouldn't the barrel burn his ear? I'm assu...
$L=T-U$ Here, $L$ is Lagrangian. T is kinetic energy. U is potential energy. But, what Lagrangian actually is? I know what Holonomic and non-holonomic is. But, I was thinking what the Lagrangian re...
I was looking for equation of motion. I came up with a solution but it doesn't satisfy me. Cause I was trying to find motion of that particle using Lagrangian. We know that $$W=\int \vec F\cdot d\...
All given metrics are for orthonormal-basis. 2 dimensional spacetime : I saw that Minkowski Metric looks like this : $$\pmatrix{-1 & 0 \\ 0 & 1}$$ or $$\pmatrix{1 & 0 \\ 0 & -1}...
We know that electrons always repel electrons. But, if somehow they collide, then what will happen? I found a related question of above one in Quora. An incoming electron can instead make them ...
Suppose we have an electric dipole of charge Q+ and Q-.The charges of the dipole are fixed (they cant move closer to each other than they already are).If we place a test particle at some distance r...
What is "disorder" in entropy? Entropy is measurement of "disorder". (Some says it's not "disorder") I had read "disorder" and "order" of entropy in my book. But I was wondering what "order" ...
In the lab I changed the angle the light hits a photoresistor and it doesnt obey Lambert's cosine law the conductivity of the photoresistor drops fast from +-20 to +-30 degrees angle.Why?
What is semiholonomic is? Holonomic actually means two point can be expressed by a equation. Non-holonomic can be expressed but, not properly. Holonomic e.g. $r^2-a^2=0$ Non-holonomic e.g. $r^2-a...
I never grokked the optics behind LightHouses and the WW2 poster below work. LightHouse beams are narrow and focussed. Doubtless, the light source can fail to illumine a seafarer or the enemy subm...
If I have a rocket with some known number of engines $n$, each producing thrust with arbitrary direction $T_n$ and center of thrust $r_n$, the total thrust amount and direction $T_{total}$ is equal...
I'm not asking about cleaning human organs here. This handheld power scrubber looks like your average rotary toothbrush! Indubitably I know that a toothbrush's brush head can be far gentler than...
I was introduced to a somewhat novel derivation of the ideal gas law that starts by thinking about the number of microstates of an ideal gas, $\Omega$. Say we have a gas with a single particle in a...
My optician counselled me I don't recommend a 1.74 index with a metal grooved frame, like the one you want from ic! Berlin, because the edge will be less resilient and be more susceptible to chi...
IKEA discontinued this NOVEMBER lamp in 2007, but I still use it. IKEA confirmed that they did not intend or design any cover or share with this lamp, and the light bulb is supposed to be exposed. ...
The major advantage of Alternating Current is that it can be transmitted to large distances without significant losses, which is not possible in Direct Current. Had economical superconducting wire...
Is it plausible to desire a "universal" calendar applicable everywhere in our universe? Must calendars be based on solar systems (Must calendars be "relational")? It might be that the universe "...
I was looking for book on classical thermodynamics. I found lot of related posts in PSE but couldn't find a book which type I was expecting. I was searching for book which covers the whole thermody...
I'm interested in knowing the surface temperature of both sides of a double-pane or triple-pane window. Given the R-value of the window, and the air temps outside and inside, how can I calculate t...
Momentum is proportional to an object's velocity, and kinetic energy is proportional to the square of its velocity $\dfrac{mv^2}{2}$. It's pretty intuitive that if object B is going twice as fast a...
I have heard the physicist Laurence Krauss claiming that he believes that the universe is flat. Okay, but if we take four astronomers and we put one in the north pole, one in the south pole, one i...
$$\sum_i F_i \cdot \delta r_i$$ is virtual work when internal force is $0$. For that reason, $$\sum_i F_i \cdot \delta r_i = 0$$ Here internal force stands for what? When a object's displacement ...
I was reading about Ether, Maxwell and Young-double-slit experiment. I got a question about Ether law. Let me say what I read about Ether Law. Suppose, a boat is traveling with Adverse of Water ...
What will happen if an electron and a proton collide? They attract each other inside an atom. But, why they don't collide inside atoms? Does the "boundary" of the nucleus push them away? depends...
I don't understand either of these Reddit comments that are still too complicated. Please simplify? Alfenhose An interesting phenomena, it is because the brain doesn't store what you saw during ...
Is this advice correct? Are they alluding to Freezing Point Depression? Adding salt to tap water lowers the Crystalloid's freezing point. Pour 3 tbsp (51 g) of salt into each of your 3 plast...
Since, there's no book category currently so, I am asking it here. And, It can be moved to that category later. I want to start learning now so, I don't want to wait. Which book is best for Clas...
In 1970, the USSR began drilling at the Kola Super-deep Borehole. The target depth was 15,000 meters; The stated areas of study were the deep structure of the Baltic Shield, seismic discontinuit...
In my notes from University the reason a material can exhibit superconducting properties is at really low temperatures electrons form Cooper pairs of which the electrons of the Cooper pairs have lo...
Should Earth's moon colonies being deep underground ensure natural heating? By natural I mean "non artificial" i.e. not from "artificial" air conditioning. The question is based on the thought th...
Would a colony on earth's moon need to be deeply underground to ensure more natural gravity (by getting closer to its core)?
Decibel level listed of solfege. Do Re Mi Fa So La Ti Do 24 27 30 32 36 40 45 80 I saw that whispering decibel level is around 40. And, normal voice level is ...
If planet 9 exists, is it correct to say that it is a "dark planet"? By "dark" here I mean to a planet that doesn't reflect enough light to easily be seen from normal telescopes (in the current co...
How can I turn this floor lamp into a reading light? I want all light exiting upwards from the lamp shade to point down. Do I just buy a mirror and put it on top of the lamp shade? Then the mirror...
Please see the images below. I owned these Mykita John glasses for three years, which feels short for glasses to break! Every day, I fold them them before placing it on my night stand and going to ...
I am having trouble understanding what a cosmic inflation is. Please try to suffice an explanation for non physicists / non formal students for physics / general audience. I understand that an ...
In Srednicki's proof of the spin-statistics theorem for scalar fields ("Quantum Field Theory", section 4), he considers interaction terms, added to the free Hamiltonian, that are Hermitian function...
I asked this question on Stack Exchange, and didn't get an answer, but maybe someone here will be able to help. In non-relativistic quantum mechanics, the normalization condition for position eige...
Let's say we have a single plate with liquid on both sides rising up due to surface tension. The meniscus formed has a radius of curvature $R$. I'm trying to find the excess pressure, i.e, the pre...
I have a question about the discussion of constrained Lagrangian systems in the book Mathematical Aspects of Classical and Celestial Mechanics by Arnold et al. (section 1.2.5). The Lagrangian syst...
In special relativity, spacetime coordinates are normally given as $$(ct, x, y, z) \tag{S}$$ with the metric being either $$g = \operatorname{diag}(-1,1,1,1) \tag{+}$$ or $$g = \operatorname{d...
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