Physics Weekly Newsletter
Physics Weekly Newsletter

Top new questions this week:

When a planet is heated through gravitational pull, where is the energy taken from?

Jupiters moon Io is heated through the gravitational pull of Jupiter, but when Io is heated because of this, where does that energy come from? How does conservation of energy work for this effect, ...

asked by Haaakon 25 votes
answered by David Hammen 27 votes

Topology of phase space

Context: From Liouville's integrability theorem we know that: If a system with $n$ degrees of freedom exhibits at least $n$ globally defined integrals of motion (i.e. first integrals), where all ...

hamiltonian-formalism topology phase-space integrable-systems  
asked by user929304 15 votes
answered by Nikos M. 3 votes

Underdetermined forces in a statics problem

I was trying to cook up a good exam problem on Newtonian mechanics, and I came up with one that I didn't fully understand myself. Always fun when you can outsmart yourself. In the figure a cylinder ...

asked by Ben Crowell 14 votes
answered by Euro Micelli 1 vote

How Earth protected from the gamma rays generated by Sun?

Sun is generating energy by nuclear fusion. And nuclear fusion will emit energy in the form of gamma rays. Normally earth's ozone filtering the Ultraviolet radiation. And magnetic fields of earth ...

sun atmospheric-science gamma-rays  
asked by sugunan 12 votes
answered by Elvex 15 votes

Center of mass frame for massless particles

Given a scattering event where a photon and electron go in and a photon and electron come out, what is the center of mass frame? I'd say, since the photon has no mass, it's the rest frame of the ...

special-relativity kinematics scattering collision  
asked by Dave 11 votes
answered by Ben Crowell 15 votes

Black hole "no hair" theorem

The "no hair" theorem (or conjecture), suggests that black holes can be entirely described by their mass, angular momentum and charge. All other details of the BH formation are lost. Is there a ...

particle-physics black-holes  
asked by Rob Jeffries 10 votes
answered by Jerry Schirmer 2 votes

Recommended books for undergraduate electrodynamics

What books are recommended for an advanced undergraduate course in electrodynamics?

electromagnetism resource-recommendations classical-electrodynamics  
asked by A.khalaf 10 votes
answered by BMS 11 votes

Greatest hits from previous weeks:

Will a blanket warm you if you are underwater?

Suppose a man falls into very cold water and gets their foot stuck under a heavy rock. Fortunately, his head is above water and someone is able to call for help. The paramedics want to keep him warm ...

water temperature thought-experiment  
asked by Moby Disk 53 votes
answered by John Rennie 69 votes

Why does the road look like it's wet on hot days?

Often, I'll be driving down the road on a summer day, and as I look ahead toward the horizon, I notice that the road looks like there's a puddle of water on it, or that it was somehow wet. Of course, ...

optics atmosphere  
asked by voithos 11 votes
answered by Lagerbaer 20 votes

Can you answer these?

SUSY QM - working out energy spectrum and wavefunctions from a given superpotential

I'm currently self-studying F. Cooper and al.'s Supersymmetry in Quantum Mechanics, and I need help working out a particular case on shape-invariance. From a given superpotential of the form ...

quantum-mechanics supersymmetry  
asked by Demosthene 1 vote

Behavior of Parahydrogen in a Magnetic Field

At low enough temperature, at equillbrium, the dihydrogen molecule is predominately parahydrogen, with the spins of the two protons opposite. Does an external magnetic field alter the ortho-para ...

spin hydrogen  
asked by DavePhD 1 vote

Gamma Spectrum: What is causing this behavior?

In my radiation detection lab we're identifying a unknown source, based on the gamma spectrum it's an activated gold foil. You can clearly see 4 peaks: 411.78 keV (Au-198), 675.93 keV (Au-198), 823.51 ...

radiation gamma-rays  
asked by T Cardew 2 votes
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