# All Questions

2answers
12 views

### Why can velocity and acceleration be negative?

Why is speed and acceleration negative when $V_1$ of an object is say 150m/s, $V_2$ is 0 m/s and $\Delta d=0.50\,\rm m$? I found the time it takes which is 0.0033s and the acceleration to be 90909.09 ...
0answers
15 views

### Is it more effective to skim through a topic then go back for details or deeply understand each concept/equation before moving on?

For example, you are going through a textbook chapter on rotational motion. You come across the concept of moment of inertia and the relevant equations for the first time. You could skim over moment ...
1answer
24 views

### Conceptual question regarding Work

Here is a problem I am having some trouble with: The solution is below, my question is, why is conservation of energy valid in this situation. From my understanding, just before the box hits the ...
2answers
27 views

### Why does moving electron emits photons?

I have read that moving or oscillating electron emits photons. But why and how does it so? And why only photons? There are other bosons like gluons, W and Z bosons, so why does electron emit only ...
2answers
16 views

### Collsion in 2D, find angle and final momentum

Suppose that the collision is inelastic. Disregard friction as the surface is smooth. Suppose that one is in the direction of $(1,0)$ and the other $(0,1)$. Is the final momentum the vector addition ...
1answer
24 views

### How to prove that any rotation can be represented by 3 Euler angles

How can one prove that any rotation of a rigid object in 3-dimensional (3D) space can be represented by a sequence of three rotations around pre-fixed axes by 3 Euler angles? I see this statement in ...
2answers
30 views

### Solution of simple problems using only Maxwell equations in differential form

Solve simple electrostatic or magnetostatic problems using only Maxwell equations. For example: In every book there is an excercise to find a magnetic field outside a thin wire of radius $a$ with ...
0answers
13 views

### finding velocity of solid particle right after collision

If a particle collides with a droplet, depending to magnitude of their velocities, different scenarios might happen: rebound, penetration, disintegration, etc. If particle starts penetrating into ...
0answers
40 views

### Why did the matter in the early universe not stick together due to gravity?

(Feel free to correct any mistaken assumptions I have) The overall question I have is: given that the early universe started as an incredibly dense ball of matter and energy, why didn't that mass ...
0answers
10 views

### Seeking Reference on Transport of Momentum by Diffusion of Mass

I'm looking at continuum mechanics from the perspective of De Groot and Mazur's "Non-Equilibrium Thermodynamics" - the first reference that I've come across that seems to do a good job of bringing ...
1answer
10 views

### Non-liniear relationship between power supplied and percieved brightness in a filamant lamp?

I was expecting the relationship between these two to be linear, but after conducting an experiment my data fits almost exactly on the curve, y = 2800.2x^2.0173, where y is the brightness in Lux and x ...
0answers
18 views

### Athletics on the moon.

The moon is a lot smaller than the earth ($\frac{1}{81}$ of the mass and $\frac{3}{11}$ of the diameter). a)How high would a professional vaulter jump on the moon? Assume that he would jump ...
0answers
16 views

### Quantum dimensions in SU(N) level k Kac-Moody current algebra

The CFT of the SU(N) level k Kac-Moody current algebra has many Kac-Moody primary fields. I wonder if any one has calculated the quantum dimensions of those Kac-Moody primary fields. I know that, for ...
0answers
35 views

### Halley's comet. (Questions from a visiting astronomer)

Okay, so we had an apparently famous astronomer in class today. He is giving lectures at our university this week and my class is one of them. So he just comes in on his first day and ends his ...
0answers
11 views

### Electron confinement energy

I was introduced the electron confinement energy. At room temperature thermal energy of a particle is about $k_B T$, where $T=298K$, giving about $25meV$. I was told that $E_{confinement}=50emV$, ...
2answers
18 views

### Does the Photoelectric Effect cause any kind of decay?

From my understanding, the Photoelectric Effect knocks electrons off of some metal using photons. Since electrons are being thrown out of the metal, does this cause some kind of decay?
0answers
9 views

### Nuclear powered flux compression generator?

A flux compression generator is a device for converting the chemical energy of explosives into magnetic field energy, with reported efficiencies of up to 20%. Is there a limit on the conversion ...
0answers
13 views

### Central Force - Trajectory

There is a central force $\vec{F}(\vec{r})=f(r)\vec{e_r}$. 1.1.: The trajectory/flight path is defined by $r=r(\phi)$, compute $f(r)$. 1.2.: The path is defined by $u=u(\phi)$ with ...
0answers
24 views

### Explanation of Interference of Electromagnetic Waves

There is a question on a test which goes like this: "Given two electromagnetic waves, one of wavelength 6.0 X 10-7 m and the other of wavelength 7.0 X 10-7 m, travelling in space. When the two ...
2answers
31 views

### 'schrodinger' picture in measurement based topological quantum computation

I am looking at the measurement processes in topological quantum computation (TQC) as mentioned here http://arxiv.org/abs/1210.7929 and in other measurement based TQC papers. Let's say I start with ...
1answer
21 views

### Coriolis Effect vs airplane

So, if I build a highway from north pole towards equator and sit in a car, speed pretty fast towards it, I should feel force with the Earths rotation due to the different rotation speeds of this ...
1answer
18 views

### Overloading stresses wooden planks beyond their elastic range, causing them to fail?

With safe use there is the fact that a car (a not so light load) can board a ship successfully going over two wooden planks. On youtube one can see this by a car boarding a ship going over two wooden ...
0answers
26 views

### My own thoughts about singularities and spacetime [on hold]

I believe the assumptions about black holes are mostly wrong due to the idea that time dilates relative to an outside observer as you get closer to the singularity at the center of the black hole. ...
0answers
7 views

### Bethe lattice nn Ising model - phase diagram

How does phase diagram for nearest neighbors ising model looks like?
3answers
83 views

### Physical reason why the derivative of a wavefunction has to be continuous?

Question What is the physical reason (i.e. without any maths) that the derivative of a wavefunction (except with infinite potentials) has to be continuous? Other info I know that in the classical ...
1answer
45 views

### If time-like paths are geodesics, what physical principle applies to space-like intervals?

If I have a number of particles interacting with one another locally, then the center of mass of the system moves along a geodesic. Taking this further with the particles interacting via an EM field, ...
0answers
19 views

### How to make wormhole? [duplicate]

Today in my Physics Class, My teacher gave us an introduction of relativity and I found this very fascinating. He Said that its very hard to make a wormhole because it requires a lot of energy. I am ...
0answers
9 views

### Effect of small changes in atmospheric pressure on open cylinder piston

OK, I'm not a physics student, but I played one for 2 semesters 35 years ago... now I'm a competitive shooter working a theory about why small changes in atmospheric conditions cause our hyper-tuned ...
1answer
22 views

### Torque in a non-inertial frame

How can we calculate torque in a non-inertial frame? Take for instance a bar in free fall with two masses, one on either end, $M_1$ and $M_2$. Taking the point of rotation to not be the center of ...
0answers
28 views

### Does the holographic principle for black holes mean that information is cloned?

When an object falls into a black hole, does the holographic principle say that the information is copied and stored on the event horizon while the original information falls in?
0answers
6 views

### Do hexagonal structure parameters vary with peaks?

Do the values of lattice constants $a$ vary with different peaks for same structure, as well for $c$, or should there be the same values for $a$ at different planes? Is there any special software ...
0answers
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0answers
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### Posibility of time travel/multiple realities/time phase shifting [on hold]

Sounds odd and unlikely, but let me explain the situation. Going on the de ja vue ideal, which we probably have all experienced, I believe things of such a matter are possible. Just today when I ...
1answer
264 views

### Calculating Kryptonian speed in the movie “Man of Steel”

This is my first question, so I'm not sure if this is the right place to ask but: How would you go about calculating the speed of Kryptonians in the movie Man of Steel (2013)? Specifically, I'm ...
1answer
26 views

### Force needed to roll wheel over edge [on hold]

I'm looking to find F. See image below. What we know: Mass of the wheel: $m = 14$ kg Wheel radius: $r = 0.32$ m What I've tried so far: $$mg + N + \sin(38.7)k = 0$$ Once the wheel ...
1answer
30 views

### Picking a guitar string of fixed length to get any nth harmonic, is it possible?

In physics textbook, we can calculate the nth harmonic of a vibrating string of a fixed length. How can we do this in a real guitar? For example, if I just pick a single open string, how can I get ...
2answers
460 views

### How do tracking detectors in particle accelerators create the pretty pictures we see?

I have read several sources about tracking detectors used in particle accelerators like LHC, but still have not found a more detailed source that can still be understood by a layperson like myself. I ...
0answers
21 views

### Relativistic Decay of Particles (Questions about Landaus derivations)

I'm currently reading Classical Theory of Fields by Lifshitz & Landau. In §11 "Decay of Particles" I can't really understand the solution to Problem 1: I have several questions: 1) How can one ...
0answers
16 views

### Problem in deriving the second term in perturbation expansion the quantum ising model

So I'm trying to derive the perturbation expansion for one particle states in the quantum ising model (Sachdev 2011 QPTs which this is derived from )  H_I= - J g \sum_i \sigma_i^x - J ...
2answers
68 views

### Why is what Heisenberg's uncertainty principle describes true?

As I understand it, Heisenberg's uncertainty principle (HUP) states that the more precisely we know the location of an electron, the less precisely we know its momentum, and vice versa. However, I've ...

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