0
votes
1answer
9 views

How to find the center of mass of several objects in a 2d plane?

We have the following scenario in a 2d plane: a big rectangle with a lot of smaller similar uniform rectangles in it, all of them weight differently. Where is the center of mass of this object ...
7
votes
4answers
3k views

Polar vs non-polar fluid

In the book "Vectors, Tensors, and the Basic Equations of Fluid Mechanics" by Rutherford Aris I read the following: If the fluid is such that the torques within it arise only as the moments of ...
0
votes
0answers
2 views

How one can know the gauge field emerging from the local gauge invariance is actually the EM field?

How one can know the gauge field emerging from the local gauge invariance is actually the EM field? I understood in a simple scalar field whose Lagrangian is given by $ \mathcal{L} = ...
6
votes
1answer
656 views

“Natural units” of mass

Gravitational attraction is given by $\frac{GMm}{r^2}$ while attraction due to electric charge is given by $\frac{q_1 q_2}{r^2}$. Why does gravity need a constant while electric charge doesn't? ...
27
votes
8answers
3k views

Classical mechanics without coordinates book

I am a graduate student in mathematics who would like to learn some classical mechanics. However, there is one caveat: I am not interested in the standard coordinate approach. I can't help but think ...
1
vote
2answers
47 views

Do unmeasured particles function the same as when measured?

If there are particles that we are uncertain of are in a state of superposition, do they still function as they would when they are measured? For instance say there is a mechanical clock, and the ...
0
votes
0answers
7 views

Interference of sound: how to calculate the sound intensity at each point?

I need help with the following question: Two speakers are sending out sound in phase with the frequency 2,13 kHz. The sound from the speakers is registered in three points A, B and C. See figure. ...
0
votes
0answers
4 views

Reconstruct the dependence of the potential from a coordinate

What is known is that an ion sent along the X-axis of a black box with a speed $V$ returns in the time of: $$T=a V^b$$ $a$ and $b$ are some known constants. Having this, can we reproduce the ...
0
votes
4answers
23 views

What happens when I place an object of certain temperature in space ? Does it loose its entire heat energy?

Can i obtain absolute zero temperature this way? And let's assume there is no cosmic microwave background and also assume that there is a way to shield the object from any heat source, such as the ...
1
vote
2answers
19 views

Do components of force have direction when doing work?

When we get angle > 0, the x-component of force is along the direction of displacement and so their product is called Work. So the x-component of force is said to have direction of the respective ...
1
vote
7answers
370 views

Can velocity be an undefined quantity?

We have the image below displaying the uniform velocity by time-distance graph. At every point velocity is constant but what if distance and time both become zero as at origin in the graph is? The ...
1
vote
2answers
39 views

I touched a tree that was touching an electric fence and got an electric shock. How is this possible if wood is an insulator?

I touched a tree that was touching an electric fence and got an electric shock. How is this possible if wood is an insulator? The tree wasn't wet, either and it was a pretty strong shock ,too.
0
votes
2answers
47 views

Can gravitational constant be changed?

In my book(Principles of Physics by Resnick,Halliday,Walker) , the authors write: If $G$ - by some miracle - were suddenly increased by a factor of 10, you would be crushed to the floor by Earth's ...
24
votes
2answers
2k views

How does light speed up after coming out of a glass slab?

As I learned today in School, my teacher told me that when light enters a Glass Slab it slows down due to the change in density and it speeds up as it goes out of the Glass Slab. This causes a lateral ...
0
votes
1answer
31 views

How experimentalists put bounds on new physics at the LHC?

I would like to understand how experimentalists search for new physics at the LHC. Lets imagine I want to use the LHC data to put a bound on the coupling of some new physics effective operator, say, ...
1
vote
2answers
64 views

Why can't unequal current sources be connected in series?

Imagine two power sources: PS-1 that can supply $5A$ at $100V$, and PS-2 can supply $10A$ at $40V$. Due to conservation of charge and Kirchoff's current law (KCL), this is incorrect, and would lead ...
1
vote
1answer
47 views

MHD Flow in a channel with and external B field and circuitry determining E. Different circuits and Ohm's law

I was wondering if someone can explain why E is the way it is in cases 2,3,4 in page 9 of these notes ? In case 2 "Short Circuit", do I just have to assume that for a perfect conductor E = 0 for ...
-2
votes
0answers
19 views

What collapsed the wave function of organic molecules for life to form?

The wave function only collapses when it is measured by an observer. So, before life came into the universe, I'm guessing that everything existed in superposition. We are told life was formed as a ...
9
votes
3answers
165 views
+100

Is the magnetic field of a white-dwarf merely residual?

Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures? Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is ...
15
votes
5answers
1k views
+500

How was the formula for kinetic energy found, and who found it?

My questions mostly concern the history of physics. Who found the formula for kinetic energy $E_k =\frac{1}{2}mv^{2}$ and how was this formula actually discovered? I've recently watched Leonard ...
10
votes
3answers
1k views
+100

How did Newton discover his third law of motion?

How did Newton discover his third law? Was it his original finding or was it a restatement of someone else's, like the first law coming from Galileo? What initiated the concept of what is now known as ...
18
votes
10answers
2k views

In reverse time, do objects at rest fall upwards?

I want to develop a game where time runs backwards, based on the idea that physical laws are reversible in time. However, when I have objects at rest on the earth, having gravity run backwards would ...
0
votes
1answer
20 views

How does resonance store vibrational energy?

In the wiki article, it is written that in resonance, maximum amplitude is possible as vibrational energy is stored. What does that statement mean? How is energy stored so that max. amplitude ...
-2
votes
3answers
35 views

Can you die from a $250 \, \mathrm V$ broken cable? [on hold]

I have a laptop power cable that is broken, my dad taped it so it is safe now. I am just wondering: would it have killed me had I touched it? If you could state your qualification/job to show you ...
0
votes
0answers
40 views

Ball flying towards me - Newton's third law is violated?

I was trying to answer the question of the flying ball here on the basis of Newtons third law and Momentum conservation. Here is what I have tried. Lets take $m_1$ (the ball) hits $m_2$ (the man). ...
3
votes
1answer
56 views

Are fundamental forces always attractive/repulsive, i.e. parallel to the separation?

If magnetic monopoles existed it would not be the case - the forces on an electron and a magnetic monopole passing by each other would be at right angles to the vector connecting the two particles! ...
1
vote
5answers
855 views

Why can't “missing mass” (=dark matter) be photons?

After a star lives and dies, I assume virtually all of its mass would be photons. If enough stars have already lived and died, couldn’t there be enough photon energy out there to account for all ...
2
votes
0answers
27 views

Lorentz transformation - Bjorken & Drell

I'm trying to derive (14.25) in Bjorken & Drell (B&D) QFT. This is $$\tag{14.25}U(\epsilon)A^\mu(x)U^{-1}(\epsilon) = A^\mu(x') - \epsilon^{\mu\nu}A_\nu(x') + \frac{\partial ...
0
votes
0answers
21 views

Discharging an electric field

Is it possible to discharge an electric field without removing the power source? I understand that electric fields have a positive charge so would it be possible to use an earthed coil to discharge ...
1
vote
1answer
24 views

Polarized light

A light is made up of electric and magnetic fields oriented perpendicular to each other. Can polarization lead to the removal of any of the field completely?
0
votes
0answers
22 views

Is nature quantized?

I was reading Planck's postulate the other day on Wikipedia and couldn't help but noticing the sentence: "...is the postulate that the energy of oscillators in a black body is quantized..." ...
2
votes
1answer
119 views

Feynman's $i \epsilon$ prescription in loop expansion

I have some questions about the $i\epsilon$ factor in Feynman diagrams. First, what is the physical meaning of $i\epsilon$ in loop amplitudes. Second, how does it ensures unitarity? And third, Dyson ...
0
votes
0answers
7 views

What is trivial and non-trivial gate in computing?

My question seems like it should be posted in Computer Engineering section, but below is how I found this word. I was reading the textbook: Quantum Computation And Quantum Information - by Michael A. ...
1
vote
3answers
28 views

Cause of rolling friction

Can you explain the cause of rolling friction? Can you tell me why, while driving a bicycle, there is less rolling friction when its tyres are fully inflated?
-1
votes
3answers
58 views

When we catch a falling object, where does its kinetic energy go?

Some of it is transformed into heat and noise, but where does the rest go? Further details: The object does not bounce off (e.g. a sack of rice marble ball). The hand remains completely static ...
5
votes
6answers
4k views

Is it possible to witness a circular rainbow?

What conditions would make it possible to see a naturally occurring fully 360° circular rainbow? Would it even be possible?
1
vote
1answer
70 views

Potential Energy of Springs and Gravity, and Work of a force

I am currently really stuck on this problem and I am not sure how to actually solve it, I think I can reason it out logically but I do not know how to show it. Here it is and under I will show what I ...
0
votes
0answers
12 views

Oscillators with anharmonic interaction terms

I'm looking for papers modeling oscillators coupled with anharmonic interaction terms. The term is combination of a linear element and a Gaussian kernel that decays proportionally to the difference of ...
0
votes
0answers
17 views

Dependence of kinetic friction on relative velocity

While I was reading my book I came across a line that tells that there is slight dependence of kinetic friction on velocity of relative motion of the bodies. Can anyone tell me how is this so?
0
votes
0answers
12 views

In MWI, how to make sense of the nonuniqueness of decomposing mixed states into pure states?

It's well known that in quantum mechanics, a generic mixed state can be decomposed into pure states in infinitely many different ways. While this property is kind of understandable if quantum states ...
0
votes
1answer
15 views

Ability to discharge static electricity

Ever since I was a child, I have been able to "discharge" static electricity in clothing by touching it. The static falls out immediately! As a child my mother would have me touch all the laundry ...
1
vote
1answer
26 views

Question concerning the diagram for stress tensor

I have a couple of questions related to the diagram in the answer by Kyle Kanos to this question, Why is stress a tensor quantity?. Q1. If the box shown is of finite size why are there not three ...
0
votes
0answers
25 views

Upper division physics lab — Project ideas [on hold]

As an experimentalist, I am very excited to be taking my first upper division physics lab next semester! The course covers basic electronics (filters, diodes, transistors, op-amps, analog & ...
2
votes
3answers
360 views

Two dimensional elastic collisions with varying angle of incident

If in an elastic collision I know all initial values and that mass for each object remains constant throughout the collision (but different from one another) how can I determine their final velocity ...
0
votes
0answers
17 views

Magnetic field due to wire and plane [on hold]

Suppose we have a wire with some current $I$ and which at a point $o$ spreads radially in all direction along conducting plane perpendicular to wire so what will be magnetic field at above and below ...
-4
votes
1answer
71 views

Could it be possible that the universe doesn't exist [on hold]

Could it be possible that the universe doesn't exist? That nothing exists, not even you or me? And by not existing, I mean totally not existing, as in not even existing as a computer simulation, or a ...
1
vote
3answers
102 views

Hawking Radiation and virtual particles

Why is energy/ mass taken away from a black hole? Doesn't the energy coming from the virtual particle come from the vacuum energy? ...if this is so, why does the black hole have to pay the energy ...
7
votes
1answer
167 views

Electric Field Change Freezing Temperature of Water?

I assume that the reason water freezes is because as you decrease the temperature, the kinetic energy of the water molecules decreases and the dipole bonding potential eventually over comes the escape ...
0
votes
1answer
83 views

Is imaginary time a fifth dimension? [duplicate]

I've read that by introducing the concept of imaginary time, the dimension of time can be treated like a spatial dimension mathematically. Assuming, without imaginary time, one considers the universe ...
1
vote
1answer
81 views

what property of steam makes it the preferable motive fluid in jet ejectors? why not air or nitrogen?

I want to know what properties of steam make it the fluid of choice in steam turbines jet ejectors. I want to understand the mechanism of energy conversion in these equipment and hence understand ...

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