# All Questions

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### General Theory of Relativity: Impact of acceleration on time, experimental setup

In What is relativity by Jeffrey Bennett (Amazon link), the author explains how acceleration/gravity impact time and causes time dilation. For this he takes an example of an accelerating space-ship ...
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### Why is the Force of Friction Equation So Simple?

The general equation for the force of friction (static or kinetic) is $F_f = \mu * F_N$, where $F_f$ is the force of friction and $\mu$ is the coefficient of friction (its value is dependent upon the ...
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### Doubt regarding limiting friction

Below is the line from my book The force of limiting friction is independent of the apparent area of contact, do long as normal reaction between two bodies in contact remain same. 1.Why is ...
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### How much heat from a fire actually warms your home?

A fire in a hearth disperses heat to, I guess, three places: the bricks of the chimney out the hearth (where the person tending the fire is standing) out the chimney, above the house How would you ...
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### Is it possible to single out a proton, electron, neutron?

I've read that it's nearly impossible to take a proton from an element. But if it's "nearly" impossible then it therefore is possible to some degree. If this has happen what exactly is the process of ...
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### Is placing a heater in the coldest part of a room the most efficient place to put it?

I've noticed that stores blow hot air in a "sheet" by doors and windows, which is "where cold air enters". I assume they do this because it saves money and/or keeps the store a uniform temperature. ...
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### Are wave functions real physical objects?

Are wave functions (ex. electron waves) real physical objects or just mathematical tools. Some researchers say that they have proof that they are real objects. Here's the link. ...
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### Why does heat lose its energy as we get further away?

Why does heat lose its energy dramatically as I move back? Say I have a fire around 0.5 meters in front of me. I can clearly feel the heat, however, as I move even very slightly back, say 1 meter ...
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### Acids and bases using electromagnetism?

Why don't we use Maxwell's equations in acids and base theory, surely the interaction between two charged species is readily described by this. The theory I have so far come across is HASB theory. ...
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### How fast am I moving?

Given the speed of light is 299,792,458 meters per second and that it is constant through out the universe. (i.e a person who measure the speed of light while standing still will get the same result ...
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### Predicting balls's movement in well due to fluid flow

I am a total newbie in fluid dynamics. In one of my experiments/open project, my experiment setup is as below: a small ball sits in a circular well (has mass density a bit heavier than water), with ...
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### What topics do I need to study to study electromagnetics on the quantum scale? [on hold]

What topics do I need to study (in order) so that I can study electromagnetics on the quantum scale? What is the name of the discipline of studying electromagnetics on the quantum scale? Do I need ...
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### How are the Lorentz force, Maxwell's third law and Faraday's law of induction clasically related?

Faraday's law of induction can be used in any situation where the magnetic flux is changing through a closed conducting loop. While giving the correct answer, it seems to me that for the following ...
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### Lightning strikes causing nudity [on hold]

Klutz's Zap Science states on p. 62: Ever Had Your Sweat Explode? A few survivors of lightning strikes — after recovering consciousness — have found themselves lying on the ground, groggy, ...
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### Where does light go when you switch it off? [duplicate]

I have a lamp. When I switch it on, it immediately illuminates the surroundings. When I switch it off, the light goes away in an instant. Why is this? Where do the light particles go? Do they quickly ...
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### Cartoon shape cutout at high velocities

I was recently reading this, and Floris's answer confirmed my knowledge that the information of an collision travels at the speed of sound. While I was thinking about that, my mind wandered and I ...
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### Measuring pressure in a container without altering it

Let's say I have a closed, non-transparent metal container with pressurized gas and I'd like to measure the pressure inside without altering it (the perssure should stay the same); is that even ...
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### What does the relation between mass and energy of a free particle mean?

what does the Hamiltonian for a free particle mean? Does it mean that the kinetic energy of the particle is in reverse relation with mass? $H$ or $E=\hbar^{2}k^{2}/2m$. Or better to ask: what's the ...
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No Nobel prizes at stake, but just an idle thought and an idle question. How could one calculate the probability of a flipped coin landing stable on its edge, instead of heads or tails? I assume ...
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### Why $D^{\mu} D^{\nu} F_{\mu \nu}=0$ ? (Noether Identity)

I have to show that: $$D^{\mu} D^{\nu} F^A_{\mu \nu}=0$$ vanish identically. This is the generalization to non Abelian groups of $\partial^{\mu} \partial^{\nu} F_{\mu \nu}=0$, apparently called ...
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### Calculating buoyant force of air experimentally

I'm planning a physics project to submit at school, and since it has to be something where we experimentally determine some value, previously known theoretically, I had this following idea but I want ...
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### Exploring beyond event horizons

In the expanding universe the velocity of separation between galaxies depends upon how far they are. If they are much far away will they have relative velocity of separation greater than speed of ...
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### Understanding the advantage of using integration over summation for finding COM for a continuous body?

My book (NCERT) writes: In a rigid body, such as a metre stick, the number of particles is so large that it is impossible to carry out the summations over individual particles. Since the spacing ...
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### Wave function in quantum mechanics

I was wondering about something while studying quantum mechanics. If the wave function collapses when measuring a particle and assumes a single position, how do we know that it was a wave in the first ...
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### Making precise the statement “particles are excitations in a quantum field”

I've been trying to self teach QFT lately. I find that the basic physical idea makes sense, and I can keep up with the mathematical formalism without too much trouble, but I'm having trouble ...
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### What are some good physics websites for learning in general? [duplicate]

As a 17-year-old who is interested in physics and especially in the laws of the universe, what are some good websites that are clear explanations and straight to the point?
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### Independence of thermodynamic variables

A given thermodynamical system has a number of state variables, not all of which are independent. Suppose that we have a system which can be specified by $k+1$ extensive variables: $U,X_1,\cdots,X_k$. ...
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### Why two-particle wavefunctions are separable and their corresponding particles are indistiguishable at the same time?

If the wavefunction $\psi(r_1,r_2)$ doesn't represents an entangled state, it is separable: $$\psi(r_1,r_2)=\psi_a(r_1)\psi_b(r_2)$$ In this treatment, we ignore the interaction between two particles ...
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### If I kept getting closer and closer to the speed of light, what would be the gravitational effects appearing like to an observer? [duplicate]

Now, with special relativity applied to the scenario of me getting closer and closer to light speed, my mass would increase with respect to the observer, and also my length would contract in the ...
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### A modern version of Landau theoretical minimum? [duplicate]

Can anyone point to me any modern books that are similar to Landau's book in scope and depth, these books used to serve as the backbone that determines one’s level of scientific culture, and since ...
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### Better gas mileage going fast or slow [duplicate]

In an automobile, do you get better miles per gallon when going faster or slower? Is this question answerable without more information? If more information is needed, assume the following: ...
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### Physics & derivatives written in a weird way

I was always taught that $\frac d {dx} (\ln x) = \frac 1 x$. No derivative had as a result any $dx$ words. In a physics book I encountered something like this (error discussion) [there might be a ...
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### How to derive the Bhatnagar-Gross-Krook collision integral from Boltzmann one?

Let's have Boltzmann collision integral: $$I_{coll} =\int d \sigma d^{3}\mathbf p_{1}(ff_{1} - f{'}f{'}_{1})|\mathbf v_{rel}|.\tag{1}\label{1}$$ How to transform $\eqref{1}$ to BGK collision ...
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### What is a nucleon field?

A nucleon is either a proton or a neutron. A field is, as John Gribbin says, a physical quantity that has a value for each point in space and time. But what is meant by a nucleon field? Can anybody ...
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### Angular velocity of disc from induced motion

I came across a question regarding linear momentum $L$ and it's conservation, however I tried and got confused. It reads: A $40kg$ girl stands on the very edge of a rotating disc of mass $50kg$ and ...
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### Mass of photon, is it possible? [duplicate]

$P=E/C$ In relativistic mechanics a Photon is defined as. $P=hf/C$ Replacing "P" $mc=hf/C$ $M=h/CT$ What does it mean, did they have mass?
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### Energy eigen value for a perturbed free particle system

Suppose we have a one-dimensional free particle system and we introduce a perturbation like $V(x)=V_{0} \cos(Gx)$, where $G$ is the reciprocal lattice vector (it's a periodic perturbation, I think) ...
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### Which program to use to draw condensed matter phase diagrams? [duplicate]

I have data in three columns: first two columns give us the (x,y) coordinate of different points and third column gives us the phase of the physical state represented by that specific point. Now, ...
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### From acceleration to displacement

Hi I am a major in Computer science and this question should be really easy for all the physics geniuses here: I have a set of data points from an accelerometer on a moving object that basically ...
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### Conservation of generalized energies in Newtonian and Relativistic Systems

I was considering the following problem: In a closed system, it is assumed that mass, momentum and energy is conserved. If we label the total mass of the System $M(i)$ at a time i, the total Momentum ...
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### How do electrons get a charge?

Electrons belong to a group of elementary particles called leptons. There are charged and neutral leptons. And electron is the charged one. But how come it got charged? The negative or positive ...
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### Magnetic field direction, Lorentz force direction?

I know that the direction of current flow can change the direction of Lorentz force, what about the direction of the magnetic field? Also, for induced current due to electromagnetic induction is the ...
Kinetic energy $E_{kin} = \frac{1}{ 2} m v^2$ may be expressed in $kg \frac{ m^2 }{sec^2}$.The formula includes squared velocity. However, instead of squared velocity = v • v it seems to be easier ...