Physics Weekly Newsletter
Physics Weekly Newsletter

Top new questions this week:

Do rainbows have ultraviolet bands and infrared bands?

We have seen that rainbows looks so colorful as we are only able to see the visible light only. Do they also have ultraviolet bands and infra-red bands, that we are unable to see? I know someone has ...

visible-light electromagnetic-radiation refraction  
asked by Shashank Sharma 35 votes
answered by engineer 46 votes

Is the Planck length the smallest length that exists in the universe or is it the smallest length that can be observed?

I have heard both that Planck length is the smallest length that there is in the universe (whatever this means) and that it is the smallest thing that can be observed because if we wanted to observe ...

spacetime quantum-gravity physical-constants discrete  
asked by George Smyridis 31 votes
answered by zeldredge 66 votes

Why do electric sparks appear blue/purple?

Electric sparks tend to appear blue or purple or white in color. Why?

electricity visible-light  
asked by Joshua Benabou 25 votes
answered by DanielLC 33 votes

Causality and how it fits in with relativity

I was talking to my teacher the other day about Einsteins space time and there's one thing he couldn't explain about the nature of Cause. I may be being stupid or just unable to comprehend, thanks for ...

asked by Oliver Cohen 16 votes
answered by Emilio Pisanty 20 votes

How many observations are needed to determine a comet's orbit?

Based on the following facts: We have Kepler's laws of planetary motion. We have a good knowledge of the positions and orbits of the gravitationally significant objects in the Solar System. We can ...

asked by Acid Jazz 13 votes
answered by WetSavannaAnimal aka Rod Vance 12 votes

What would be the rate of acceleration from gravity in a hollow sphere?

Lets say the Earth is hollow and you are in the center of it (Same mass except all of it is on the outside like a beach ball) If you move slightly to one side now your distance is closer to that side ...

newtonian-gravity planets  
asked by Joe 13 votes
answered by Marcel 26 votes

Black Body Golf Balls

The surface of a golf ball has about 35% more surface area (than a similar sphere) due to its dimples. So my question is simple, given identical radius, ideal black body material, and temperature: ...

thermal-radiation thought-experiment  
asked by Samuel 10 votes
answered by Travis 2 votes

Greatest hits from previous weeks:

With Newton's third law, why are things capable of moving?

I've got a rather humiliating question considering newton's third law "If an object A exterts a force on object B, then object B exerts an equal but opposite force on object A" -> $F_1=-F_2$ ...

newtonian-mechanics forces free-body-diagram faq  
asked by user16458 44 votes
answered by AndrewC 66 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?

Holding magnet near CRT monitor damages the screen?

Few days ago I tried keeping my magnet in front of my CRT monitor screen and it was showing some cool effects like showing so many different color but then when I removed it ,that blurr effect was ...

asked by Shashank Sharma 2 votes

Fermionic path integral on the disk - Recovering the vacuum state

I'm trying to get a better feel for the operator to state map in quantum field theory. There is a general claim for 2d theories that doing the path integral on a disk with no operator insertions gives ...

quantum-field-theory path-integral fermions  
asked by childofsaturn 3 votes

Conservation Laws and Isotropic Time

In most dynamics books I've read they refer to conservation laws and their associated symmetries. I know that the conservation of momentum is a result of the homogenity of space angular momentum is ...

newtonian-mechanics conservation-laws noethers-theorem  
asked by user4203532 2 votes
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