Physics Weekly Newsletter
Physics Weekly Newsletter

Top new questions this week:

Can we theoretically balance a perfectly symmetrical pencil on its one-atom tip?

I was asked by an undergrad student about this question. I think if we were to take away air molecules around the pencil and cool it to absolute zero, that pencil would theoretically balance. Am I ...

quantum-mechanics newtonian-mechanics momentum uncertainty-principle stability  
asked by TBBT 53 votes
answered by mmesser314 81 votes

Why doesn't light, which travels faster than sound, produce a sonic boom?

I know that when an object exceeds the speed of sound ($340$ m/s) a sonic boom is produced. Light which travels at $300,000,000$ m/s, much more than the speed of sound but doesn't produce a sonic ...

electromagnetism speed-of-light acoustics  
asked by I Studied At Hogwarts 37 votes
answered by user77487 32 votes

Static electricity and door handles

I have a pair of shoes, which seem to isolate me from the ground. In effect I'm gathering static charge and every time i grab an aluminum door handle, that current discharges and that hurts. Ouch. I ...

electricity  
asked by Spook 26 votes
answered by user 5061 42 votes

Does it take more energy to open a door when applying force close to the hinge?

Assuming an ordinary hinged door (without any springs), would it take more energy to open it when applying force in the middle of the door (point b), rather than at the end of the door (point a), ...

newtonian-mechanics forces energy rotational-dynamics  
asked by JonathanReez 23 votes
answered by Ali Moh 14 votes

Why does moving through time not require energy?

Moving through the other three dimensions necessitates energy. But why doesn't moving through time necessitate energy?

energy dimensions  
asked by I Studied At Hogwarts 20 votes
answered by pela 51 votes

Why doesn't the evening/morning sun feel much hotter on your face?

I understand that places on the Earth's surface get hotter in summer, and in the middle of the day rather than morning or evening, because the surface of the Earth is presented 'face-on' to the Sun at ...

energy radiation atmospheric-science  
asked by jwg 16 votes
answered by santiago 27 votes

Black hole with two singularities?

I hope this question isn't too naive, but would it theoretically be possible to have a black hole with 2 singularities (or 2 black holes at the same location). If this is possible, would there be any ...

general-relativity black-holes singularities  
asked by Mark N 15 votes
answered by John Rennie 16 votes

Greatest hits from previous weeks:

How exactly does time slow down near a black hole?

How exactly does time slow down near a black hole? I have heard this as a possible way of time traveling, and I do understand that it is due in some way to the massive gravity around a black hole, but ...

general-relativity black-holes time reference-frames  
asked by Annika Peterson 18 votes
answered by Larian LeQuella 21 votes

Relation between water flow and pressure

Is there any equation that states the relation between pressure and water flow. I.e. Let's say that in 1 hour with 8mca (water collum meters) pressure I obtain 50m3. What if (giving the same ...

fluid-dynamics pressure water flow bernoulli-equation  
asked by Paulo Bueno 1 vote
answered by Ron Maimon 9 votes

Can you answer these?

Problem on Einstein - de Haas experiment

I am a Physics student (4th year) and I'm trying to study the Einstein - de Haas effect in laboratory. That is what I got: a suspended Iron cylinder with about 5 cm height and a radius of 0.8 cm is ...

experimental-physics measurement  
asked by Crazydemon 2 votes

Could Navier-Stokes equation be derived directly from Boltzmann equation?

I know how to derive Navier-Stokes equations from Boltzmann equation in case where bulk and viscosity coefficients are set to zero. I need only multiply it on momentum and to integrate it over ...

fluid-dynamics statistical-mechanics  
asked by Name YYY 4 votes

How are resonating valence bond (RVB) states related to fractional quantum Hall (FQH) states?

In Kalmeyer and Laughlin's paper, there is an argument made for a frustrated two-dimensional Heisenberg antiferromagnet on a triangular lattice that if one uses a FQH wavefunction for bosons to ...

condensed-matter research-level quantum-hall-effect  
asked by Saavanth Velury 3 votes
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