1
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1answer
30 views

Michleson Interferometer fringe shift

I have a problem with interferometer fringe shift. I am learning it from my physics book. In the book, it is written, "As the L1 (Displacement of moveable mirror) is changed, the pattern of ...
1
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2answers
61 views

Why an impact exerts so much force? [closed]

If an object of velocity $v$ and mass $m$ moves towards a resting object of mass $M$, then if the object which is hit might break. Why? What is the reason that a collision has more power than a ...
1
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1answer
48 views

Why does imaginary periodic time of the Rindler space of black hole give Hawking temperature?

The metric of a Schwarzschild black hole in Rindler coordinates is $$ds^2= -\frac{\rho^2}{(4MG)^2} dt^2 +d\rho^2 + d\mathbf x_\perp$$ where $\rho$ gives us the distance to the horizon. If we switch ...
1
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1answer
20 views

The instability of dry friction

Based on Newton Dynamics, the kinetic force of friction of any moving object can be found by using formula, $$F_f = \mu_k F_N $$ This means that if $\mu_k$ and $\ F_N$ remains constant, the ...
1
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1answer
46 views

Solenoid vs coil of wire

This may sound pretty basic, but: I'm studying for my AP Physics exam, and I am confused. Apparently, the formula for the magnetic field in the center of a loop of wire with $n$ turns is: $B=\frac{\...
1
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2answers
141 views

What is the inconsistency between Maxwell's electrodynamics and newtonian mechanics?

As far as I understand, when a modification of a theory is made it is because some observation required this modifcation. Quantum Mechanics is a nice example of that: observations of microscopic ...
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2answers
88 views

Centripetal force: if radius decreases, does ANGULAR or TANGENTIAL velocity change?

Having conceptual trouble with this aspect of centripetal force. Say we have a puck on a frictionless table attached to a string that I am holding through a small hole, so that the puck moves in a ...
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2answers
58 views

How can an accelerating inclined plane prevent a block on it from sliding?

If I increase the force $F$, only the normal force $N1$ acting on $m1$ would increase which has no component along the plane, ie. along $m1gsin\theta$, so how would applying this force prevent m1 from ...
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2answers
55 views

Does the constancy of the speed of light in vacuum hold for any observer in GR as well?

From SR, we know that the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. But in GR, does it still hold for all observers? I mean the constancy ...
1
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1answer
51 views

Finding inclined plane acceleration

In the above diagram, both the surfaces are frictionless. The force exerted by $m_1$ perpendicular to the inclined plane $m_2$'s surface is $m_1g\cos\theta$, and the horizontal component of that force ...
1
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1answer
66 views

How does Compton scattering demonstrate particle over wave behavior?

Why is Compton scattering thought to demonstrate light's behavior as a particle over that as a wave. I'm interested in the thoughts at the time of Compton, but also how it contradicts current theory ...
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1answer
25 views

Why do certain mesons not self-destruct? [duplicate]

As I understand it, particles and antoparticles annihilate one another. But some mesons (and pions?) consist of a quark and its antiquark. How can they exist without the two particles annihilating ...
1
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1answer
64 views

Can particle quantum spin be described with a wave function? [closed]

I'm a little confused about the idea of spin. It's been non-technically described to me as "like magnetic dipole moment", except only two possible "directions". But I feel like that's a bad analogy, ...
1
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1answer
74 views

Homoclinic orbit and a particle in a double well

The physical set-up is a classical particle in a parabolic double well: Physically, a particle with reasonable amount of potential energy would be able to roll down the slope of the well, roll past ...
1
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1answer
148 views

Difference between theoretical equations and empirical equations

Some equations are theoretical in the sense that they are derived from an underlying theory. Other equations are empirical in the sense that they were selected only because they fit experimental data ...
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2answers
77 views

Tension and friction. Cool question

I had an exercise like the image, where block A is pulled by a force F, there is that rope(tension) attached to the block B and the wall, and there is friction between A and B, and A and the ground, ...
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1answer
58 views

Many questions about expanding of the space

Sorry if my grammar is a bit off. But I have few questions about space and its expansion. If space expands faster and faster all the time, will there be a time when we cannot see further than "hubble ...
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3answers
38 views

Relationship Gravitational Potential and the Tangential Velocity of a Satellite

So gravitational potential is given by $V(r)={\frac{GM}{r}}$ and the tangential velocity of a satellite is the square root of $V$, i.e. $\sqrt V$. So how do these two relate, if at all?
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2answers
52 views

Why water's temperature is less than air?

I measured the temperature of water and found that it's less than room temperature. I think evaporation is the main reason of it. Are there any reason except evaporation for the less temperature of ...
1
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1answer
33 views

Conservation of momentum (angular and translational) [closed]

A ring of radius $R$ and mass $M$ lies on its side on a frictionless table. A bug of mass $m$ rests on the ring. The bug starts walking on the ring with constant speed $v$ relative to the ring. ...
1
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2answers
72 views

Why don't people use Hamilton's equations for a relativistic free charged particle?

A charged relativistic free particle has the Hamiltonian in general: $$ \mathcal{H} = \sqrt{p^2c^2+m^2c^4}.$$ I read somewhere that says, it is possible to go further and say that the EoM are ...
1
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1answer
44 views

Kirchhoff's laws in phasor domain

While analysing AC circuits, we write voltage, current etc all with complex numbers namely "phasors". While studying the same, I wondered if Kirchhoff's laws held good with current and voltage in ...
1
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1answer
39 views

D2O distribution in water [duplicate]

I just learned that about 1/1000 of hydrogen is deuterium. Does that mean 1/1000 of water is D2O, which is heavier and sinks to the bottom in a glass of water? And consequently is there a layer of D2O ...
1
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1answer
28 views

Is it possible to measure the spin of an electron without moving it?

I know that the position and spin operators commute, so it is theoretically possible. What I want to know is, what experiments currently exist that achieve this?
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1answer
30 views

Tensile strength of a chain of electromagnets

I was having a discussion about the tensile strengths of various materials. Could something like a chain of electromagnets be made to have a tensile strength proportional to the power applied to it?
1
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1answer
128 views

Deriving Pauli Matrices

How does one derive using, say, the operator formula for reflections $$ R(r) = (I - 2nn^*)(r),$$ the reflection representation of a vector $$ R(r) = R(x\hat{i} + y\hat{j} + z\hat{k}) = xR(\hat{i}) +...
1
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1answer
45 views

Structure of Mass Renormalisation

I'm currently working on the renormalisation part in Peskin, Schroeder QFT. There it is stated that non-logarithmic UV divergences give a mass renormalisation and thus are forbidden, e.g. for the ...
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2answers
75 views

How is a mass, suspended vertically by two springs in parallel, kept stable? [closed]

Consider a mass suspended vertically from above by two springs in parallel with different spring constants. Wouldn't the tension be different in each spring? How is this system kept in equilibrium?
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1answer
46 views

Representation of Symmetry group

Suppose the SE $\boldsymbol{H}\psi=E\psi$ describes a closed system and $G$ is a symmetry group of the system. Then any transformation in $G$ leaves the form of the SE invariant. It seems plausible to ...
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1answer
37 views

Can angular momentum not be conserved in a straight line motion?

Consider a particle moving an a straight line, with constant velocity $v$. The angular momentum (pivot point $O$) can be calculated as $$L=mr v_{\theta}$$Where $v_{\theta}$ is the velocity ...
1
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1answer
44 views

How does the surface of a material always break inversion symmetry?

I am trying to visualize this for an HCP structure. Take the profile view as such: just working in 2d. So my understanding is if we can take a point (x,y) -> (-x,-y) and get the same crystal than ...
1
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1answer
49 views

Amplitude of damped driven harmonic oscillator [closed]

I have a question that I can reason physically but mathematically I am not sure if my approach is correct. The amplitude of the oscillator is: $$A(\omega) = \frac{QF_{0}}{m}(\frac{1}{\omega_{0} \...
1
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1answer
40 views

What is $bfr$ in this expression?

I am reading 'Fundamentals of Quantum Mechanics' by Sakir Erokoc and came across this expression in relation to transition probabilities: $$\vec p=e \langle \psi_b |bfr|\psi_a \rangle$$ Which can be ...
1
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1answer
97 views

Spinning a string with a mass on the end. What makes the mass rotate parallel to the ground? [closed]

Say you use your hand to rotate a string with a mass attached to the end. The string will first become taunt and then the mass and string will move upwards until they are spinning parallel to the ...
1
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1answer
19 views

How much load does an aqueduct support?

Recently, I found out about /r/InfrastructurePorn, and I found a particularly interesting photo of the Gouwe Aqueduct in Gouda, NE: It seems like the bridge that is supporting the boat wouldn't be ...
1
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1answer
23 views

Electrostatics - System of parallel plates

For a system of $n$ parallel metal plates bearing charges $q_1, q_2,\dots, q_n$, why it is so that the facing surfaces of the plates bear equal and opposite charges? How do we prove that?
1
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1answer
70 views

Plane Wave Solutions of the Dirac Equation

I'm trying to understand the plane wave solutions of the Dirac Equation. But I'm still a newbie on indices notation and contravariant and covariant objects. What I don't understand is how to get: $$(\...
1
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1answer
45 views

Why is the center of mass frame always used in rigid body dynamics?

In most of the cases the center of mass is chosen for rigid body motion description, but this is not an obliged choice, since the motion of any point $P$ of the rigid body can be seen as the ...
1
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1answer
55 views

I want to increase pressure of water in a closed vessel [closed]

I am trying to make a high pressure water jet using DIY hand pump which pushes water into a sealed vessel with non-return valve at the inlet. I am planning to do it by first closing the valve to the ...
1
vote
3answers
84 views

What is the maximum reach distance of electric field? [duplicate]

if i charge small object by removing electrons and put that object in the middle of huge vacuum chamber (million of light years in size) does the electric field lines of that charged object still be ...
1
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2answers
31 views

Projects to undertake Using Lasers [closed]

I need an economically feasible physics project that would use lasers in any manner preferably with respect to optics for a school projects class XII . Any suggestions are welcome no matter how crazy ...
1
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3answers
67 views

Could we use solar energy with endothermic reactions to fight global warming? [duplicate]

Im in holidays in Malaysia and it is god damn hot. You cannot leave your hotel/car and go out. All this because of the sun. I we were to capture all the heat (solar panels, ...) would this help make ...
1
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1answer
98 views

Energies in Band Alignments

There is something that I would like to confirm regarding the energy when aligning the bands of heterostructures. There seems to be a general consensus that there is no simple rule to align two ...
1
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2answers
80 views

Assuming there is no wind, do two raindrops of different sizes fall at the same speed?

Assuming there is no wind, do two raindrops of different sizes fall at the same speed? Simple enough question. Look forward to your answers.
1
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1answer
46 views

Can the curvature of the Universe be a function of time?

Apologies for the repetition here, but can our Universe experience (either physically or mathematically) non-constant curvature that is a function of time?
1
vote
1answer
97 views

Deriving the Spinor Completeness Relation without using a Representation

Reference: DAMTP problem set 3, question 5 but ignore the spinor solutions given. To preface, this has taken up 1 entire day and a further 2 afternoons of work so I will just list the most promising ...
1
vote
1answer
31 views

Adjoint momentum Dirac equation

So we have the commonly quoted momentum space version of the Dirac equation and the adjoint Dirac equation: $$ (\gamma^{\mu}p_{\mu}-m)u=0 $$ Often, we are asked to show that the adjoint momentum ...
1
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3answers
76 views

What force prevents particles from penetrating other particles?

I understand that what prevents objects from penetrating each other is the electromagnetic force between the electrons in the respective objects. But if we don't have electrons, for example a proton. ...
1
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3answers
84 views

Why doesn't a swing make a full revolution on a swingset in a park? [closed]

I'm familiar with the concept of swinging of a swing in a park, but I'm confused why it doesn't it swing at a complete circle around the center bar?
1
vote
1answer
96 views

What is the desest material on earth? [closed]

Apart from the elements, do we know of materials that are denser? I.e. can an alloy be denser than the sum of its compounds, for example if the new lattice packs denser than each of the compounds it's ...

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