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Q&A

General Q&A about physics of any type and at any level

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60%
+1 −0
Signal modeling as only digital, only analogue, or as both

In signal processing, are signals modeled in only one way (digitally or analogously) or are there some signals which can be modeled in both ways?

3 answers  ·  posted 2y ago by deleted user  ·  last activity 2y ago by Lundin‭

60%
+1 −0
Conductivity with angle of light

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?

1 answer  ·  posted 2y ago by MissMulan‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+4 −1
Why should there not be water below 6kms in the Earths crust?

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...

0 answers  ·  posted 3y ago by Conrado‭  ·  edited 3y ago by Conrado‭

60%
+1 −0
What does Laplace operator represent?

I was wondering what's the physical meaning of Laplace operator. $\vec\nabla$ actually represent a field. I had seen that Laplace operator is written as $\vec \nabla \cdot \vec\nabla=\nabla^2=\Delt...

1 answer  ·  posted 2y ago by deleted user  ·  last activity 2y ago by deleted user

40%
+0 −1
If planet 9 exists, is it correct to say that it is a "dark planet"?

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...

2 answers  ·  posted 3y ago by deleted user  ·  last activity 2y ago by HDE 226868‭

71%
+3 −0
How can the kinetic energy equation be intuitively understood?

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...

3 answers  ·  posted 2y ago by gmcgath‭  ·  last activity 2y ago by celtschk‭

42%
+1 −2
Is it plausible to desire a "universal" calendar applicable everywhere in our universe?

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 "...

3 answers  ·  posted 2y ago by deleted user  ·  edited 2y ago by Trilarion‭

71%
+3 −0
Calculating Max humidity for a house

I want to write some code to control my whole house humidifier. I want my code to calculate the percentile relative humidity above which dew will form on my windows. I have sensors for air tempera...

0 answers  ·  posted 2y ago by re89j‭

60%
+1 −0
What happens if an electron collides with another electron?

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 ...

0 answers  ·  posted 2y ago by deleted user

71%
+3 −0
What is "order" and "disorder" in entropy?

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" ...

2 answers  ·  posted 2y ago by deleted user  ·  last activity 2y ago by Derek Elkins‭

80%
+6 −0
What is inflation in cosmology?

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 ...

2 answers  ·  posted 3y ago by deleted user  ·  last activity 3y ago by deleted user

50%
+1 −1
What's the equation of kinetic energy of charged particle?

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\...

1 answer  ·  posted 2y ago by deleted user  ·  edited 2y ago by deleted user

66%
+2 −0
What is Ether theory? (I think the book I read is misinterpreting Ether)

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 ...

2 answers  ·  posted 2y ago by A person who doesn't know anything‭  ·  edited 2y ago by A person who doesn't know anything‭

80%
+6 −0
How do constraints work in Lagrangian systems?

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...

1 answer  ·  posted 3y ago by Technically Natural‭  ·  last activity 3y ago by Derek Elkins‭

40%
+0 −1
Explain like I'm 5 – After glancing at a clock, why does the first second sometimes feel longer than the rest? [closed]

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 ...

0 answers  ·  posted 3y ago by TextKit‭  ·  closed 3y ago by Mithrandir24601‭

66%
+2 −0
Should Earth's moon colonies being deep underground ensure natural heating?

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...

1 answer  ·  posted 3y ago by deleted user  ·  last activity 3y ago by Dave Tweed‭

75%
+4 −0
Is it possible to derive the Dieterici equation starting from assumptions about microstates?

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...

0 answers  ·  posted 2y ago by HDE 226868‭

75%
+4 −0
What is the meaning that the universe is flat?

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...

2 answers  ·  posted 2y ago by deleted user  ·  last activity 2y ago by celtschk‭

60%
+1 −0
Superconductivity

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...

0 answers  ·  posted 2y ago by MissMulan‭

50%
+0 −0
Where did the measuring systems (metric & imperial) originate and how? [closed]

I had a thought that crossed my mind a while back that went something like this: It's a cool thing measurements exist, if there wasn't, there'd be trouble and we'd be counting atoms if we could....

0 answers  ·  posted 2y ago by General Sebast1an‭  ·  closed 2y ago by Mithical‭

60%
+1 −0
Clear up confusion on Minkowski signature

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}...

1 answer  ·  posted 2y ago by deleted user  ·  edited 2y ago by deleted user

42%
+1 −2
Does folding glasses increase the probability of separating at the hinge?

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 ...

1 answer  ·  posted 3y ago by TextKit‭  ·  last activity 3y ago by Olin Lathrop‭

60%
+1 −0
What's the importance of Poisson brackets?

$$F=F(q,p,t)$$ $$\frac{dF}{dt}=\frac{\partial F}{\partial q}\frac{\partial q}{\partial t}+\frac{\partial F}{\partial p}\frac{\partial p}{\partial t}+\frac{\partial F}{\partial t}$$ $$=\frac{\part...

0 answers  ·  posted 2y ago by deleted user  ·  edited 2y ago by deleted user

20%
+0 −6
Are lamps, with blistering light bulbs exposed and facing down on the user, dangersome?

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. ...

2 answers  ·  posted 2y ago by TextKit‭  ·  last activity 2y ago by celtschk‭

50%
+0 −0
Prove differential form of Lagrangian

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}^...

1 answer  ·  posted 2y ago by deleted user  ·  last activity 2y ago by celtschk‭

50%
+0 −0
What is $\mathcal{O}$ in integration of potential?

I saw following equation in Griffiths EM $$V(r)=-\int_\mathcal{O}^r \vec E \cdot d\vec l$$ While the surface was closed but not symmetrical circular. At first I was thinking $\mathcal O$ was repr...

1 answer  ·  posted 2y ago by deleted user  ·  last activity 2y ago by deleted user

40%
+0 −1
Is it rational to freeze water bottles during colder nights, and place them in front of a fan during warmer days?

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...

1 answer  ·  posted 3y ago by TextKit‭  ·  last activity 3y ago by manassehkatz‭

71%
+3 −0
Calculate Center of Thrust

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...

1 answer  ·  posted 2y ago by Josh Hyatt‭  ·  last activity 2y ago by Olin Lathrop‭

71%
+3 −0
Interaction terms in Srednicki's proof of spin-statistics theorem

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...

1 answer  ·  posted 3y ago by Technically Natural‭  ·  last activity 3y ago by Mithrandir24601‭

42%
+1 −2
Book suggestion for Classical Mechanics

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...

1 answer  ·  posted 2y ago by deleted user  ·  last activity 2y ago by deleted user

66%
+2 −0
Why we can't find a particle accelerating unless there's some other particle accelerating somewhere else?

I was reading "Introduction to classical Mechanics" by David Morin. In that book they wrote that The third law says we will never find a particle accelerating unless there’s some other particle ...

3 answers  ·  posted 2y ago by deleted user  ·  last activity 2y ago by Olin Lathrop‭

30%
+1 −5
How dangerous is mounting and firing a gun on another human's body part? [closed]

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...

1 answer  ·  posted 3y ago by TextKit‭  ·  closed 2y ago by Mithical‭

66%
+2 −0
Motion of charged particle inside a magnetic field

We have place a charged particle of 2C with mass 2kg, 1mm above a current-carrying wire of 1A.The charged particle has an initial velocity of 100m/s The magnetic field of the wire for simplicity w...

0 answers  ·  posted 2y ago by MissMulan‭  ·  edited 2y ago by MissMulan‭

81%
+7 −0
Unusual way to write spacetime coordinates/metric: Is there any downside?

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...

1 answer  ·  posted 3y ago by celtschk‭  ·  last activity 3y ago by dmckee‭

50%
+0 −0
What is Apsidal Vector?

I have recently heard of Apsidal Vectors. I was searching about it through internet. I had found the video in YT. I had found similar question in PF. But, the PF answer wasn't clear to me. I am jus...

0 answers  ·  posted 2y ago by Anonymous‭

50%
+0 −0
Magnetic charges to solve interaction between 2 magnetic dipoles

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...

1 answer  ·  posted 3y ago by MissMulan‭  ·  last activity 3y ago by Olin Lathrop‭

66%
+4 −1
What does Lagrangian actually represent?

$L=T-U$ 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...

2 answers  ·  posted 2y ago by deleted user  ·  last activity 2y ago by deleted user

66%
+2 −0
What happens if an electron collides with a proton?

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...

2 answers  ·  posted 2y ago by deleted user  ·  edited 2y ago by deleted user

50%
+1 −1
Natural ways to acquire gravity for a colony on earth's moon

Would a colony on earth's moon need to be deeply underground to ensure more natural gravity (by getting closer to its core)?

2 answers  ·  posted 3y ago by deleted user  ·  last activity 2y ago by Canina‭

66%
+2 −0
Applying Young-Laplace equation on meniscus formed due to rise of liquid on a single plate

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...

0 answers  ·  posted 3y ago by TripleFault‭

40%
+0 −1
decibel level of human hearing(human-auditory-range)

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 ...

1 answer  ·  posted 3y ago by deleted user  ·  last activity 3y ago by Olin Lathrop‭

60%
+4 −2
Would we need Alternating Current if superconducting wires existed?

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...

2 answers  ·  posted 3y ago by theabbie‭  ·  last activity 3y ago by celtschk‭

80%
+6 −0
How does probability conservation work in Dirac's original formulation of relativistic QM?

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...

1 answer  ·  posted 3y ago by Technically Natural‭  ·  last activity 3y ago by Derek Elkins‭

57%
+2 −1
Why would a 1.74 index lens be more prone to chip and be less resilient than 1.67?

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...

1 answer  ·  posted 3y ago by TextKit‭  ·  last activity 3y ago by Olin Lathrop‭

40%
+0 −1
How can I turn a floor lamp, that lights upward, into a reading light? [closed]

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...

0 answers  ·  posted 3y ago by TextKit‭  ·  edited 3y ago by TextKit‭

25%
+0 −4
For cleaning food and objects, power scrubber vs. Electric rotary toothbrush? [closed]

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...

0 answers  ·  posted 3y ago by TextKit‭  ·  closed 3y ago by Mithrandir24601‭