# All Questions

0answers
10 views

### The Earth's gravitational magnetics

The Earth has magnetic properties correct, so can they be measured and if so what are some consistencies?☆
0answers
6 views

### What is the importance of $2d$ supersymmetric gauge theory?

I have been working $2d$ $N=(2,2)$ theories focused on checking duality like, Seiberg duality (2d version: named "Hori-Tong" duality) and its extension. During the study i got $2d$ $N=(2,2)$ ...
1answer
17 views

### Quantum field operators in HEP and CMT

For a real scalar field (which is a bosonic field) we have these commutation relations : $\left[\phi(x,t),\phi(y,t)\right]=0 \qquad \qquad \left[\phi(x,t),\pi(y,t)\right]=\delta(x-y)$ but in ...
1answer
167 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 ...
4answers
106 views

### Bullet Cluster and MOND

Apparently the Bullet Cluster is some slam-dunk proof of ΛCDM. The argument seems to be that most (>90%) of the baryonic mass in these clusters is in the form of X-ray emitting gas. Therefore the ...
3answers
29 views

### Why does water reflect light?

why water reflects light? What is actually happening when light is reflected by water? How water reflects light. We know why metals reflects light. But water is not metal though it reflects light as ...
2answers
406 views

5answers
5k views

### Divergence of $\frac{\hat{r}}{r^2}$

In David J. Griffiths's Introduction to Electrodynamics, the author gave the following problem in an exercise. Sketch the vector function $$\vec{v} ~=~ \frac{\hat{r}}{r^2},$$ and compute ...
1answer
109 views

### Why does plastic wrap grow, then shrink, then grow again when microwaved?

The other night I was reheating a bowl of leftovers in the microwave. There was a fair amount of liquid in the bowl, so I covered the bowl with plastic wrap when I put it in the microwave. When I put ...
1answer
20 views

### What is the physical significance of Rapidity in Relativistic kinematics?

Recently I have came across a new term called rapidity in relativistic kinematics. We are using it in relativistic kinematics due to its additivity whereas velocity is not a additive quantity in ...
2answers
33 views

2answers
30 views

### Nuclear to Electricity Energy Conversion

Currently nuclear power generates heat, which heats water into steam that turns conventional turbines. The energy conversion is as follows: photonic->heat->kinetic->electric This would result in low ...
1answer
434 views

### Why does the Nusselt Number for a Constant Surface Temperature, Thermally Fully Developed Circular Pipe Converge To a Constant of 3.66?

I have flow in a pipe with a constant surface temperature boundary condition. The velocity profile is fully developed and the temperature profile is also fully developed. In my textbook, it says that ...
0answers
13 views

### Torque when net external force is zero

I was studying force couple and my teacher said that in this the torque about any point is same. That led me to wonder if in any case if net external force is zero then is torque about any point in ...
0answers
24 views

### What does not have mass and can not absorb light?

Can anyone answer my question or prove it impossible?
2answers
18 views

### Exercise pulleys and accelerations

The system shown has ideal massless pulleys and no friction. The pulleys 1 and 2 are fixed and the pulley 3 is mobile. The mass m2 is rigidly attached to the center of the pulley 3 by a support ...
1answer
206 views

### Is the passive reference configuration different from the conventional direction of current?

Is the passive reference configuration different from the conventional direction of current? According to the passive reference configuration, current enters the positive polarity of voltage, while ...
1answer
31 views

### Why does the water level go down when a dense object is moved from a boat to the bottom of the pool [duplicate]

Imagine you have a container ship with an extremely heavy mass on it. Why does the water level on the ship drop when the mass is placed in water?
3answers
386 views

### A few questions about the concept of work

From Wikipedia: The work done by a constant force of magnitude F on a point that moves a displacement d in the direction of the force is the product: $$W = Fd.$$ If I lift some object from a ground, ...
0answers
11 views

### Classical - quantum analogy of Berry phase

I am reading this webpage about Berry phase: http://materia.fisica.unimi.it/manini/berryphase.html I am happily convinced about the first "elementary geometry" example they provide. Now I am trying ...
7answers
4k views

### Intuitively, how can the work done on an object be equal to zero?

To my understanding the work done on an object is defined mathematically as: $$W = \vec{F}\cdot\vec{S}=|\vec{F}||\vec{S}|cos\theta$$ This, I understand. My problem is that I don't understand that if ...

15 30 50 per page