Physics Weekly Newsletter
Physics Weekly Newsletter

Top new questions this week:

"Falling upward" - how far you have to be from Earth to start falling to the Moon?

Talking about gravity with my 9 y/o she asked when do we start "falling upward" to the Moon. What is the distance at which the Moon's gravitational attraction is higher than that of the Earth and thus ...

homework-and-exercises newtonian-mechanics newtonian-gravity solar-system celestial-mechanics  
asked by rafb3 33 votes
answered by Rob Jeffries 21 votes

Why did "tickling the dragons tail" by Louis Slotin not cause an explosion?

I have been reading the excellent Command and Control by Eric Schlosser and discovered more about Louis Slotin's experiment with "tickling the dragons tail" and the infamous Demon Core. What I don't ...

nuclear-physics  
asked by dooburt 27 votes
answered by WetSavannaAnimal aka Rod Vance 27 votes

How much air needs to be displaced to generate an audible sound?

I'm reading a book where in one scene a wizard/alchemist teleports a scroll after reading. He folded the parchment carefully and muttered a single cantrip. The note vanished with a small plop of ...

acoustics air displacement  
asked by npst 27 votes
answered by Floris 38 votes

What do we see while watching light? Waves or particles?

I'm trying to understand quantum physics. I'm pretty familiar with it but I can't decide what counts as observing to cause particle behave (at least when it's about lights). So the question is what do ...

quantum-mechanics particle-physics visible-light waves wave-particle-duality  
asked by martincpt 26 votes
answered by John Rennie 53 votes

Melting diamond and cool down as diamond

Is it possible to melt diamond? And if possible while let it cool will it became diamond again?

thermodynamics material-science diamond  
asked by sugunan 17 votes
answered by Floris 38 votes

Hourglass on the Moon

Someone asked me this, and I was surprised to find I couldn't answer it: suppose I have an hourglass / egg timer that times two minutes in Earth's gravity. If I used it on the Moon, how long would it ...

newtonian-mechanics newtonian-gravity everyday-life  
asked by Nathaniel 15 votes
answered by pentane 4 votes

What does this depiction of a black hole in the movie Interstellar mean?

I was expecting a whirlpool in 3D and the matter glowing from friction as it nears the center, as I expected a event horizon to be negligible visually. How does this depiction work? How big is the ...

general-relativity black-holes event-horizon geodesics  
asked by aitchnyu 13 votes
answered by Chris White 13 votes

Greatest hits from previous weeks:

Why are volume and pressure inversely proportional to each other?

It makes sense, that if you have a balloon and press it down with your hands, the volume will decrease and the pressure will increase. This confirms Boyle's Law, $ pV=k=nRT $. But what if the ...

thermodynamics pressure ideal-gas volume  
asked by Andres Riofrio 4 votes
answered by Colin K 5 votes

What is a good introductory book on quantum mechanics?

I'm really interested in quantum theory and would like to learn all that I can about it. I've followed a few tutorials and read a few books but none satisfied me completely. I'm looking for ...

quantum-mechanics resource-recommendations  
asked by PhaDaPhunk 21 votes
answered by Man 27 votes

Can you answer these?

Is work done on a fluid in a communicating vessel necessarily equal to work done by the fluid inside it?

During the explanation of Pascal's law the argument that work done by a force to move the fluid inside communicating vessel is equal to the work done by the fluid at the other end of the vessel was ...

fluid-dynamics pressure work  
asked by Viham G 1 vote

Ohm's Law for Accelerated Conductors

My questions are about the Ohm's law for a moving conductor in a stationary magnetic field. As we know this law is stated based on following relation with respect to the fixed frame of reference ...

electromagnetism special-relativity  
asked by MAEQEng 2 votes

What is the largest number of bosons placed in a BEC?

What is the record for the largest number of bosons placed in a Bose-Einstein condensate? What are the prospects for how high this might get in the future? EDIT: These guys reported 20 million ...

bose-einstein-condensate  
asked by Jess Riedel 6 votes
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