All Questions

-1
votes
1answer
36 views

What are the Calculus that I needed in Classical Physics? Will I be having a difficulty? (See image of this thread)

As I am starting my class, I am wondering what is the math needed for my class “Classical Physics”. I was not given a bridging and my Baccalaureate course is Bachelor of Secondary Education Major in ...
0
votes
1answer
59 views

Particle physics threshold energy

I read the article Threshold energy on Wikipedia about colliding particles and their threshold energy. Consider the case where a particle 1 with lab energy $E_1$ (momentum $p_1$) and mass $m_1$ ...
-1
votes
0answers
21 views

A block of mass 2kg is moving with a velocity of 2i-j+3k m/s. find the magnitude and direction of momentum of the block with the x-axis [on hold]

Please answer it. It is a question of momentum. a block of mass 2kg is moving with a velocity of 2i-j+3k m/s. find the magnitude and direction of momentum of the block with the x-axis
0
votes
0answers
28 views

What stimulates pair production? [duplicate]

I read that it happens when passing a nucleus or an electron, but why does that cause pair production to take place?
0
votes
1answer
40 views

What if there was no baryon-antibaryon asymmetry in our universe?

We know that the universe goes through different evolutionary phases: radiation, matter and later dark energy epoch. What would happen if there was no baryon-antibaryon asymmetry? How would the ...
1
vote
1answer
30 views

Application in medical field

I have heard about many new developments in radiotherapy for treating cancer/tumors such as hadron therapy but why can't we use wave interference for it? Incoming waves could interfere destructively ...
1
vote
1answer
54 views

Question on electric flux

In the first diagram(given below), the charge should not feel any force as the electric fields are not touching it. But now if we see the flux throw an imaginary cube, it will give out an electric ...
0
votes
0answers
27 views

Charge density of infinite sheet of negative charge in presence of external charge

A tiny hole is made in an infinite, conducting sheet of charge. Assume initial charge density to be $-\sigma$. We put a positive charge $+q$ in this hole. Find the charge density of the sheet now as a ...
2
votes
0answers
30 views

Thermal hysteresis and its physical significance in lipid membranes?

We usually associate the phenomenon of hysteresis with memory in the system. For example, magnetic hysteresis is the basis of hard disks(if I recall it correctly). There are also electronic circuits(...
0
votes
0answers
24 views

A pendulum consists of a rod with length L and a coin of mass m

A pendulum consists of a rod with length $L$ and a coin of mass $m$. The pendulum is held in a horizontal position and then is released with a minimum velocity needed to make a full circle. What'...
-1
votes
0answers
11 views

How much amount of induction should occur?

Consider a conductor placed in a constant external electric field. Electrons within the conductor redistribute themselves till the internal electrical field (due to polarization of charge) will equal ...
-1
votes
0answers
75 views

The spring paradox: Is there any rational transformation for the relativistic force?

A simple thought experiment crossed my mind a few years ago for which I could not as yet find a convincing answer: Assume that a mass-less spring $S_1$ with (proper) constant $k_0$ hangs from the ...
-1
votes
1answer
25 views

A bar weighs $2N$ and is $5m$ in length. What is the weight needed to balance the bar?

A bar weighs $2N$ and is $5m$ in length. What is the weight($M$) needed to balance the bar? I think I understand that the equation not including the weight of the bar would have $$3*3=(5*1)+(2*M)\...
1
vote
0answers
24 views

Energy of a three-dimensional system

The energy of a three-dimensional system of dimensions $L_x$, $L_y$, $L_z$, is given by, $$\varepsilon\left(n_{x}, n_{y}, n_{z}\right)=\frac{\hbar}{2 m}\left[\left(\frac{\pi n_{x}}{L_{x}}\right)^{2}+\...
2
votes
3answers
636 views

Why do we use a cylinder as a Gaussian surface for infinitely long charged wire?

Why do we use a cylinder as a Gaussian surface for infinitely long charged wire and not some other shape like cube?
-1
votes
0answers
38 views

What is this text talking about (about change of spacetime co-ordinate systems)?

I'm completely lost on the last paragraph. What expanding sphere thing are they talking about? I have no idea. Can someone explain this text part by part?
3
votes
6answers
172 views

How can beta plus decay be possible?

$\beta +$ decay is where a proton gets turned into a neutron and a positron and a neutrino. However, a neutron is heavier than a proton, so obviously this reaction is endothermic. So then, why does ...
0
votes
0answers
14 views

Electric current dipole moment

Electrical Current Dipole of dipole moment $\mathbf{p_{EC}}$ has unit of $A\cdot m$. My knowledge of dipole moments unfortunately stopped in high school where I learned that dipole moment $\mathbf{p}$ ...
0
votes
3answers
34 views

Fermi level in metals and semicoductors

As we read about Fermi energy, it is the energy of the highest occupied electrons. But if we look at the energy level diagram of semiconductor the Fermi level is situated somewhere between the valence ...
0
votes
0answers
23 views

Conductance Charged Box

A box with thick and conductive sides with dimensions: Lx, Ly, Lz- while LZ>>Lx,Ly. The long dimension of the box [Lz] can be viewed as infinite so Phi(x,y,z)=Phi(x,y) Given that: Phi(0,y)=-Phi(Lx,...
1
vote
1answer
35 views

Radius vs speed for flywheel energy storage

If I understand the formula correctly, the equation for kinetic energy of a flywheel is $mw^2r^2$ whereas the formula for "centrifugal force" is $mw^2r$. So how come so much focus is on the speed of ...
0
votes
1answer
33 views

Writing a two variable function$ f(x,t)$ in terms of Dirac-Delta $δ(x)$ function and a function $P(t)$?

How to write a two variable function $f(x,t)$ in terms of Dirac-Delta $\delta(x)$ function and a function $P(t)$? For example; I read something in a book. You can find the following picture. But ...
0
votes
0answers
12 views

Physics-y resource request on Killing-Cartan forms

Most books that treat nonabelian gauge theory do not contain detailed discussion on Killing-Cartan forms, they'll usually just say that in $\text{SU}(N)$ Yang-Mills theory, one can choose generators $...
0
votes
0answers
20 views

Acoustics in heterogeneous medium: Reflection and Tranmission

I am trying to understand the effect of changing impedance on acoustic pressure wave. I have attached the image from the book "Fundamentals of Acoustics"(Kinsler et. al)(r1 and r2 are the impedance of ...
2
votes
1answer
32 views

Choosing initial condition for Hamilton-Jacobi PDE

For separable solutions to Hamilton-Jacobi PDE (say in 2D), we treat the Hamilton's principal function $S$ as $$S= W(x) + W(y) - E*t$$ and treat the separate parts as constants and find $W(x)$, $W(y)$...
0
votes
3answers
54 views

How do I understand Kinetic energy formula? [duplicate]

$$\frac{mv^2}{2}= Kinetic Energy$$ Can you explain me? What is purpose of $v^2$, $mv^2$, I am trying to understand the formula.
0
votes
0answers
27 views

Acoustic Plane Wave

Consider an ideal fluid which we have a spherical object on it and a progressive plane wave is heading the object. I have a simple question and it is: If we assume the amplitude of the incident ...
1
vote
0answers
20 views

Adding new fermions to a two-dimensional space

Suppose we have a two-dimensional space where we can seat electrons. Now, is it so that even before we start adding electrons the single electron energy levels already exist and as soon as we begin ...
0
votes
2answers
76 views

Is there differential form notation for Maxwell's equation in curved spacetime?

In special relativity, Maxwell's equations may be written as \begin{align*} dF = 0, \\ \star\, d\star F = J. \end{align*} In four-vector notation, this translates to $\partial_{\mu}F^{\mu\nu} = J^{\nu}...
-2
votes
0answers
37 views

My new equation of motion is right or wrong [on hold]

Every equation includes acceleration, but form the three equations I made forth equation of motion.![enter image description here](https://i.stack.imgur.com/IUrcH.
0
votes
2answers
30 views

Why there are three reactions at fixed beam in F.B.D?

It is fixed so no reactions will be present, then how three reactions at fixed beam in F.B.D? In F.B.D, we draw two reactions and moment reaction at fixed beam: Why there are three reactions at ...
1
vote
2answers
73 views

Why is effective mass a tensor?

So I came across the effective mass concept for solids the other day. It was mentioned that the effective mass is a tensor and may have different values in different directions. However, this is stark ...
0
votes
1answer
23 views

How will a polar molecule affect another molecule nearby, why it feels a relatively large force?

Mean position of the negative charges and positive changes are not at the same point (polar molecule) how will that affect another molecule nearby, why it feels a relatively large force? Will the type ...
0
votes
1answer
30 views

Is friction a conservative force when a ball rolls down an inclined plane(pure rolling)?

My book says friction is non dissipative for a cylinder rolling down an inclined plane,so is it conserved?
1
vote
1answer
41 views

Nuclear Physics Question

How could I calculate the chance of a proton actually joining the nucleus and 2 protons and 3 and so on? Assuming a large number of protons are fired at a substance?
0
votes
0answers
27 views

How small does a hole in a cup have to be to hold water without dripping? [duplicate]

I am creating a drain that lets water in but keeps pieces of plastic out. I need to know the size of a standard water droplet.
3
votes
1answer
44 views

In Feynman lecture Vol1. chapter12 about friction, $F = μN$ will fail because of the excessive heat generated. Why is that?

$F = μN$ will fail because of the excessive heat generated if the normal force or the speed of motion gets too big. Why is that? "$F = μN$, where μ is called the coefficient of friction (Fig. 12-1)....
0
votes
1answer
56 views

Oscillating spring, speed close to the equilibrium: How is this answer not 1.5? [on hold]

I have this question with the answer listed as $2.0\,\mathrm{m/s}$. "A $1.25\,\mathrm{kg}$ mass on a spring with a constant of $12.0\,\mathrm{N/m}$ is oscillating back and forth. Its maximum ...
1
vote
1answer
30 views

Klein-Gordon equation propagators: intersection with the support of the source

Let $(M,g)$ be a globally hyperbolic. Let $P = \Box - m^2$ be the Klein-Gordon differential operator. Following Fewster's notes, we may define the retarded/advanced propagators $$E^\pm : C^\infty_0(M)\...
0
votes
1answer
55 views

Muzzle Velocity of a Bullet out of a Barrel

We want to know the speed of a bullet, in feet per second, for a given round. We know the weight of the bullet, volume of the casing, amount of gun powder, length of the barrel, and diameter of the ...
1
vote
1answer
49 views

Tadpole diagrams in 1-loop massive scalar amplitudes?

Consider a massive scalar diagram such as or The loop momentum enters and exits the tadpole vertex, so that in the first diagram the momentum in the propagator connecting the two vertices is zero ...
0
votes
1answer
27 views

Does magnetic field make particle move in the direction of magnetic field(In circles)?

So my task says A particle with mass $m$ moves freely through space and there is no electromagnetic field. At moment $t = 0$ a uniform magnetic field is turned on with field strength $B$, and ...
0
votes
0answers
6 views

In Feynman lecture vol1,chapter12 friction between two wet glasses, is there any atmospheric pressure related during the process?

In Feynman lecture vol1,chapter12 friction between two wet glasses, is there any atmospheric pressure related during the process? Does the water between two glasses make use of atmosphere pressure? Or ...
0
votes
0answers
44 views

How far can a crow fly?

This question is all about order of magnitude estimation. All of my undergraduate physics classmates (and myself of course) were presented this question one afternoon (my god, that was over 50 years ...
1
vote
1answer
54 views

Entanglement of Werner States

Let the Werner state $$\rho_W = W\mid\Psi^-\rangle\langle\Psi^-\mid + \frac{1-W}{4}\mathbb{I},\ W\in [0,1],$$ where $|\Psi^-\rangle=(|01\rangle-|10\rangle)/\sqrt{2}$. I have repeatedly heard that ...
1
vote
1answer
31 views

Derivation of Raychaudhuri equation - Trace

In Wald (Wald: General Relativity on page 218, equation 9.2.10) is stated that $$v^c∇_cB_{ab}=−B^c_bB_{ac}+R^d_{cba}v^cv_d $$ and to continue in order for the equation to be derived one needs to take ...
0
votes
2answers
33 views

Radio wavelength to penetrate 8 ft of seawater

I am trying to penetrate about 8 ft of seawater with a radio wave. What wavelengths will work? I understand that low wavelengths penetrate seawater the best, but I am looking for a frequency that does ...
0
votes
1answer
49 views

Pendulum attached to Oscillating Fulcrum

In the specific scheme, I would expect that by pulling the spring to the right, the pendulum due to inertia would have to move to the left quartile. In order to find the r vector: $$r = R + l$$ and ...
0
votes
0answers
22 views

Resources on Physical Baryon States as mixings of multiplet states

I've been told, and have seen in papers (search for "mixing") that baryon resonances are not plucked from pure group theoretic multiplets, but are most often found to be mixings of states in different ...
-3
votes
3answers
109 views

Fire in my building [duplicate]

If there is a fire in a building and I am on 10th floor and I can't exit the building.Is it safe to jump out of the window with a chair and when chair is close to the ground I just jump of the chair ...

15 30 50 per page