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1500 questions
141
votes
28 answers
How can you weigh your own head in an accurate way?
I read some methods but they're not accurate. They use the Archimedes principle and they assume uniform body density which of course is far from true. Others are silly like this one:
Take a knife then remove your head.
Place it on some scale
Take…
user5402
- 3,113
141
votes
8 answers
What is $\Delta t$ in the time-energy uncertainty principle?
In non-relativistic QM, the $\Delta E$ in the time-energy uncertainty principle is the limiting standard deviation of the set of energy measurements of $n$ identically prepared systems as $n$ goes to infinity. What does the $\Delta t$ mean, since…
Hobo
- 1,435
141
votes
12 answers
Why does my tea periodically alternate its rotational speed after stirring? (Link to video below)
I noticed that after stirring, a bubble in the centre of my mug of tea changed the speed it was rotating at periodically. Speeding up, then slowing down, then speeding up again, etc. Almost like when a ballerina pulls in her arms to increase her…
luke
- 1,107
140
votes
5 answers
What does it mean for two objects to "touch"?
If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of
"I'm not actually touching you! The electrons in the atoms of my
skin are just getting really close to yours!"
Expanding on this a…
Thomas Shields
- 1,522
139
votes
15 answers
Is the butterfly effect real?
Is the butterfly effect real? It is a well-known statement that a butterfly, by flapping her wings in a slightly different way, can cause a hurricane somewhere else in the world that wouldn't occur if the butterfly had moved her wings in a slightly…
Deschele Schilder
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139
votes
2 answers
On this infinite grid of resistors, what's the equivalent resistance?
I searched and couldn't find it on the site, so here it is (quoted to the letter):
On this infinite grid of ideal one-ohm resistors, what's the equivalent resistance between the two marked nodes?
With a link to the source.
I'm not really sure if…
Malabarba
- 5,201
- 5
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138
votes
2 answers
Reading the Feynman lectures in 2012
The Feynman lectures are universally admired, it seems, but also a half-century old.
Taking them as a source for self-study, what compensation for their age, if any, should today's reader undertake? I'm interested both in pointers to particular…
David Feldman
- 1,481
137
votes
5 answers
Why does paper cut through things so well?
Paper is an extremely flexible material, at least when it is in sheet form. It will deform significantly according to the pressure applied and it is easy to fold.
Therefore, it's extremely counterintuitive that a sheet of paper could cut through…
137
votes
15 answers
How can anything ever fall into a black hole as seen from an outside observer?
The event horizon of a black hole is where gravity is such that not even light can escape. This is also the point I understand that according to Einstein time dilation will be infinite for a far-away-observer.
If this is the case how can anything…
Matt Luckham
- 1,767
137
votes
10 answers
Why the Principle of Least Action?
I'll be generous and say it might be reasonable to assume that nature would tend to minimize, or maybe even maximize, the integral over time of $T-V$. Okay, fine. You write down the action functional, require that it be a minimum (or maximum), and…
Jonathan Gleason
- 8,834
136
votes
21 answers
Books for general relativity
What are some good books for learning general relativity?
Pratik Deoghare
- 5,665
135
votes
2 answers
Why does ice cream get harder when colder?
What would seem to be a silly question actually does have some depth to it. I was trying to scoop out some of my favorite soft name-brand ice cream when I noticed it was frozen solid, rather than its usual creamy consistency. After leaving it out…
TheEnvironmentalist
- 2,794
134
votes
1 answer
Linear sigma models and integrable systems
I'm a mathematician who recently became very interested in questions related to mathematical physics but somehow, I faced difficulties in penetrating the literature... I'd highly appreciate any help with the following question:
My aim is to relate…
user5831
- 1,331
133
votes
8 answers
Does a particle exert force on itself?
We all have elaborative discussion in physics about classical mechanics as well as interaction of particles through forces and certain laws which all particles obey.
I want to ask, does a particle exert a force on itself?
EDIT–
Thanks for the…
Shreyansh Pathak
- 3,405
133
votes
3 answers
Why is the vibration in my wire acting so oddly?
I was soldering a very thin wire today, and when I had one end firmly soldered, I accidentally bumped the wire diagonally with my tweezers. What I'd expect to happen is that the wire oscillates for a little while in one axis, then stops. However,…
0xDBFB7
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