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1500 questions
36
votes
5 answers
Jumping into water
Two questions:
Assuming you dive head first or fall straight with your legs first, what is the maximal height you can jump into water from and not get hurt?
In other words, an H meter fall into water is equivalent to how many meters…
Uri
- 2,130
36
votes
2 answers
Why isn't temperature frame dependent?
In (non-relativistic) classical physics, if the temperature of an object is proportional to the average kinetic energy ${1 \over 2} m\overline {v^{2}}$of its particles (or molecules), then shouldn't that temperature depend on the frame of reference…
user114806
- 639
36
votes
3 answers
Theory behind patterns formed on Chladni plates?
In this video of vibrating Chladni plates we can see small sand particles align themselves into different interesting patterns (also shown in the image below) which correspond to some particular vibrations.
What is the theory behind this fact? Are…
Beni Bogosel
- 685
36
votes
4 answers
Swimming in Spacetime - apparent conserved quantity violation
My question is about the article Swimming in Spacetime.
My gut reaction on first reading it was "this violates conservation of momentum, doesn't it?". I now realize, however, that this doesn't allow something to change its momentum; it only allows…
Keenan Pepper
- 7,817
36
votes
2 answers
To what degree of precision are atoms electrically neutral?
It is said that if, say, the electric charge is not a Lorentz invariant, neutral atoms are no longer neutral, which is not experimentally valid. I want to know to what degree of precision atoms are measured to be electrically neutral and what would…
Mohammad Javanshiry
- 2,802
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- 27
36
votes
10 answers
Is coherent light required for interference in Young's double slit experiment?
In this Veritasium video, a home experiment is presented which appears to produce a very good double-slit interference pattern with normal sunlight.
The experiment is an empty cardboard box with a visor and a placeholder for a microscope slide with…
AnimatedPhysics
- 658
36
votes
7 answers
Can spinning arms really help you balance on the edge of a cliff?
This is how many cartoons depict a character about to fall from the edge of a cliff. You can see movie characters do it. You can also see real people doing it. But does spinning arms like that actually help you to gain balance?
It would, ( through…
AlphaLife
- 13,439
36
votes
1 answer
Zero modes ~ zero eigenvalue modes ~ zero energy modes?
There have been several Phys.SE questions on the topic of zero modes. Such as, e.g.,
zero-modes (What are zero modes?, Can massive fermions have zero modes?),
majorana-zero-modes (Majorana zero mode in quantum field…
wonderich
- 8,086
36
votes
5 answers
Why do we observe particles, not quantum fields?
My understanding is that, in the context of quantum field theory, particles arise as a computational tool. We perform an expansion in the path integral in some parameter, and the terms in these expansions correspond to Feynman diagrams which can be…
Charles Hudgins
- 1,600
- 9
- 16
36
votes
7 answers
Why do people still talk about bohmian mechanics/hidden variables
I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal variables as yet unknown which determine its…
yayu
- 4,982
36
votes
3 answers
If aerographite is lighter than air, why doesn't it float?
Air is 6 times denser than aerographite but looking at pictures or videos presenting the material, I see it resting on tables rather than raising to the ceiling.
Also, since the material is made of carbon nanotubes, I assume there are empty spaces…
Youcha
- 465
36
votes
12 answers
Is it correct to say that it is theoretically impossible for perfect rigid bodies to exist?
If perfect rigid bodies were to exist, then consider a scenario in which two rigid bodies of equal masses moving with velocities of equal magnitude but opposite in direction colliding against one another. During the collision, the velocities of both…
Mathew_
- 548
36
votes
3 answers
In superluminal phase velocities, what is it that is traveling faster than light?
I understand that information cannot be transmitted at a velocity greater than speed of light. I think of this in terms of the radio broadcast: the station sends out carrier frequencies $\omega_c$ but the actual content is carried in the modulated…
Approximist
- 1,203
36
votes
10 answers
Why are only infrared rays classified as "heat rays"?
I've often heard that Infrared rays are called "heat rays". However, I feel like this term is a misnomer. Don't all the wavelengths of electromagnetic radiation carry energy?
Judging by how gamma rays are highly penetrating and are dangerous when…
Cross
- 3,360
36
votes
7 answers
When I put my hand on a hot solid why don't the particles transfering heat to my hand exert a force on it?
When I put my hand on a hot metal (say) solid, I can feel my hand heating up. I suspect this is caused mostly by particles (electrons, atoms, ...?) from the solid colliding with the particles that make up my hand thereby transferring kinetic energy…
Damian Birchler
- 535