# All Questions

3answers
1k views

### Physics book recommendations for transition to PhD study

Now in the end of my MSc in physics I've been contemplating in enrolling in a Phd in theoretical physics. Before that I think I would do best to re-study some subjects. My question is then, what books ...
4answers
388 views

### What forces are at play when molecules wiggle (due to heat)?

What forces are at play when molecules wiggle (due to heat)? Or in other words, What makes them move?
3answers
3k views

### Relation between Newtons and Kilograms

Work is expressed as W=F*d, where the F is in Newton, d is in meters and result ...
4answers
117 views

### Why uncharged particles do not feel the Lorentz force? [closed]

Why uncharged particles do not feel the Lorentz force? Please do not answer with the formula $\vec F = q\left( \vec E + \vec v \times \vec B \right)$. Edit after an answer which is an circular ...
3answers
313 views

### Differences between wavefunction, probability and probability density?

I am trying to understand the differences between wavefunction, probability and probability density. There are different definitions on the internet. For example: ...
2answers
68 views

### Is fission reaction considered natural or artificial? [closed]

As I learned, nuclear fission doesn't occur without the control of a human made nuclear reactor, by hitting a neutron to a fissile isotope. Thus, the fission reaction is considedred as a part of ...
1answer
125 views

### Why are laws of physics always of product forms?

A first observation is that all the extant laws of physics are of product forms. This phenomenon is somewhat intriguing. The question is: why do law of physics always take, instead of a sum of two ...
1answer
135 views

### why countries can't make nuclear bombs? [closed]

Somehow when I google about the nuclear bombs I find a lot of books and resources that seem to explain everything about how those bombs are made. But sometimes I often hear that countries that want to ...
1answer
106 views

### Apply the Heisenberg Equation to the Hamiltonian [closed]

$\frac{d}{dt}$$\hat{H} = \frac{i}{\hbar}$$[\hat{H},\hat{H}]$ +$\frac{\partial{\hat{H}}}{\partial{t}}$ That's as far as I've got. I do not know much about the Heisenberg equation or even what it ...
1answer
290 views

### Commutator with Pauli spin matrices and the momentum operator

How is $\left[\vec\sigma \cdot \vec p, \vec \sigma \right]$ proportional to $\vec \sigma\times \vec p$, where $\sigma$ are the Pauli spin matrices and $p$ is the momentum operator?
1answer
108 views

### Can a wave exist on the “face” of a wave?

It would seem that this would be possible with waves in water. What about other waves Clarification: Given a wave starting from a point of impact, in water, at: Time 0:00 and xyz 0,0,0 and the ...
3answers
2k views

### Collision between electron and proton?

What would happen if an electron collided with a proton such that the two do not collapse? Would the two become a unit, or would some force prevent them from bonding thus forcing the electron to orbit ...
2answers
185 views

### How many mirrors placed perpendicular to each other shall make a light ray completely reverse its path?

The answer is 3. But according to me 2 shall also work in 2 Dimensions? Does anyone has a theoretical proof?
2answers
228 views

### How does artificial gravity reduction (weightlessness) work on Earth?

Some of us have been to those amusement park/carnival/theme park rides where you enter some capsule/machine, and you will float, etc. There is also some other thing where you go inside a big room ...
2answers
161 views

### Scaling: Gravity and Friction

I understand how doubling the length of a shape quadrupes it's area and the analog in 3 dimensions. My question however relates to other physical quantities, for example gravitational field strength. ...
1answer
88 views

### Dark Energy Explanation Found [closed]

It's my sincere request to this Physics forum that if i am wrong (which has the least possibility atleast from my side) just reply "wrong" so that i can move on futher. I know personal theories are ...
1answer
118 views

### Why nuclear tests move under ground since 1964?

According to this database: http://www.ga.gov.au/oracle/nuclear-explosion.jsp Since 1962, 99% of USA Nuclear tests was underground. Since 1964, 99% of Soviet Nuclear tests was underground. Is it ...
5answers
4k views

### Is it possible to generate electricity using a water tower?

Is it possible to build a water tower that will provide enough pressure to run an electricity generator? A water pump can be used to send water up to the tower. The water pump can be powered by solar ...
3answers
1k views

### Right hand rule to measure direction of electric field [closed]

The diagram: a positive plate is on the left of the page and a negative plate is on the right. The velocity of the particle is going down the page. So, with a right hand rule, I would point my thumb ...
2answers
909 views

### How to determine Center of Gravity? [closed]

I came across this question while having conversation with one person. We know that Center of Gravity of a solid cube is at the intersection of connecting the opposite vertex of the cube. Suppose, you ...
2answers
480 views

### How to visualize a 3D scalar function? [closed]

In physics, we regularly deal with observables, which are functions $f(x,y,z)$ of the position vector $\vec r = (x,y,z)$. How, do you plot such a function? For functions $y=f(x)$ of 1 parameter, we ...
1answer
3k views

### Can I use AA batteries to charge iPhone? [closed]

Technically, 4 AA batteries will give out ~5V, which is equivalent to USB. Can you use 4 AA batteries to charge an iPhone, without messing up the Li-Ion cells used on iPhone? So my question really ...
2answers
249 views

### Is Dark Energy converted to Gravitational Potential Energy?

Dark Energy is basically doing work against gravity to accelerate the expansion of universe. So, for time-translational symmetry to be hold, dark energy must be converted to gravitational potential ...
1answer
182 views

1answer
155 views

### Behaviour of liquid in vaccume

Is it possible for a liquid to exist in a high quality vacuume? For example, a few Torr. If so what are the methods for doing this?

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