## Top new questions this week:

### Is there any aspect of an explosion resulting from a nuclear weapon test that cannot be simulated using super computers?

This Washington Post news article states that with the advent of computer simulation of nuclear tests, live tests are no longer needed. Generally speaking there are 3 aspects of an explosion ...

nuclear-physics simulation computational-physics explosions

### Why do particles in the molten wax near a burning candle wick get pushed away?

Have a look at this clip I made of my candle burning: I can accept that the molten wax gets sucked into the wick (though not quite sure why: capilary action?). But why does it also seem to get ...

thermodynamics fluid-dynamics everyday-life combustion

### How does a wire carry alternating current?

Consider a simple network of a bulb whose two terminals are connected to two wires with open ends A and B respectively A o--------💡--------o B Now if a DC current source is attached across A and ...

electricity current conductors

### How to keep a helium balloon between 1 to 5 meters above ground? (without it being tied)

I understand that helium balloons rise because their density is less than air, so they can rise up to a point where the air surrounding it has the same weight as the balloon. I was thinking to fill it ...

atmospheric-science air buoyancy hydrostatics

### The maximum distance for which Coulomb's law has been verified?

We know that Coulomb's law, $F_{12} = \frac{kq_1q_2}{r^2}$, was experimentally verified for small distances by Coulomb himself at the and of the XVIII century. The question is what is the maximum ...

forces electrostatics experimental-physics coulombs-law

### The final parsec "problem"

Many and perhaps all galaxies seem to contain supermassive black holes of about $10^7 M_\odot$ at their centres. Determining their origins is of great astrophysical interest. In what I understand to ...

general-relativity black-holes astrophysics galaxies gravitational-waves

### Can momentum have a complex expectation value?

I'm making examples of wave functions to incorporate in a QM exam. I came up with the following wave function, which gives me some troubles: \psi(x,0) = \begin{cases} A(a-x), & -a \leq x \leq ...

quantum-mechanics mathematical-physics operators uncertainty-principle distributions

## Greatest hits from previous weeks:

### Why is AC more "dangerous" than DC?

After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...

electricity everyday-life current

### Finding the force of friction of a moving object and its change when it accelerates to a constant speed

I have been searching for a straight forward answer to this question for ages now and it is driving me crazy. Here is what I know: If an object is moving at a constant speed the force of friction ...

acceleration friction velocity

### Are all maximally symmetric spacetimes constant curvature spacetimes?

A $d$ dimensional maximally symmetric spacetime is a spacetime with the maximum allowed number of Killing vectors. This number is $\frac{d(d+1)}{2}$. Constant curvature spacetimes are spacetimes ...

general-relativity differential-geometry symmetry curvature vector-fields

### Can one measure experimentally the average distance between the two electrons in the excited state of helium in the singlet versus triplet states?

$\frac{1}{\lvert\ \vec(r_{1})-\vec(r_{2})\rvert}$ is a hermitian operator so I am supposing there could potentially be an observable with this which might be experimentally measured. We can measure ...

quantum-spin atomic-physics spectroscopy
So I use a home-built Pulsed Laser Deposition(PLD) system to deposit metal oxide thin films. I use a $248\ \mathrm{nm KrF}$ laser. I recently deposited two films under slightly different conditions. ...