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1500 questions
72
votes
3 answers
How can ants carry items much heavier than themselves?
This morning I saw an ant and suddenly a question came to my mind: how do ants actually carry items much heavier than themselves?
What's the difference (in physics) between us and them?
Paul
- 3,455
72
votes
6 answers
Why is the sky never green? It can be blue or orange, and green is in between!
I, like everybody I suppose, have read the explanations why the colour of the sky is blue:
... the two most common types of matter present in the atmosphere are
gaseous nitrogen and oxygen. These particles are most effective in
scattering the…
user59485
71
votes
7 answers
How come neutrons in a nucleus don't decay?
I know outside a nucleus, neutrons are unstable and they have half life of about 15 minutes. But when they are together with protons inside the nucleus, they are stable. How does that happen?
I got this from wikipedia:
When bound inside of a…
Aria
- 1,077
71
votes
5 answers
Could the observable universe be bigger than the universe?
First of all, I'm a layman to cosmology. So please excuse the possibly oversimplified picture I have in mind.
I was wondering how we could know that the observable universe is only a fraction of the overall universe. If we imagine the universe like…
A. P.
- 3,231
71
votes
9 answers
Why do fans spin backwards slightly after they (should) stop?
Today, I've decided to observe my PC fan as I shut the computer down. The fan slowly lost angular momentum over time. What I've found really interesting is the fact that the momentum vector change did not stop at the zero vector, but instead flipped…
Captain Trojan
- 803
71
votes
3 answers
Why does water falling slowly from a tap bend inwards?
This is something anyone could easily verify. When we open a tap slowly, water bends inwards (towards the axis) while maintaining its laminar flow. After a certain height below the opening, the flow becomes turbulent. I've approximately illustrated…
Vishnu
- 5,266
71
votes
7 answers
What's the physical meaning of the statement that "photons don't have positions"?
It's been mentioned elsewhere on this site that one cannot define a position operator for the one-photon sector of the quantized electromagnetic field, if one requires the position operator have certain formal properties. This is a theorem that…
knzhou
- 101,976
71
votes
3 answers
Why is dry soil hydrophobic? Bad gardener paradox
When I forget to water my plants, and their soil becomes very dry, during the next watering I can see that the soil becomes hydrophobic. I can even see pockets of air between the repelled blob of water and the soil.
On the contrary, when the soil is…
user46147
- 3,014
71
votes
3 answers
Why does a lot of water vapour come suddenly after the heat source of boiling water is removed?
I have noticed this several times. When I am boiling water, a few seconds before its boiling point, vapours are formed as usual. But if I turn the gas off before boiling, the moment it turns off, I see a lot of vapours being formed all of a sudden…
Abha Vishwakarma
- 741
71
votes
5 answers
Conformal transformation/ Weyl scaling are they two different things? Confused!
I see that the weyl transformation is $g_{ab} \to \Omega(x)g_{ab}$ under which Ricci scalar is not invariant. I am a bit puzzled when conformal transformation is defined as those coordinate transformations that effect the above metric transformation…
vishmay
- 1,116
71
votes
3 answers
How big would my telescope have to be if I wanted to see the Mars rover from my backyard?
I imagine that with a big enough telescope, I would be able to zoom in and see the Mars rover in enough detail to make out the details (like the wheels, cameras, etc.). How large would the telescope have to be? (or how can I calculate this value?)
Josh
- 1,315
71
votes
5 answers
Why does a system try to minimize its total energy?
Why does a system like to minimize its total energy? For example, the total energy of a $H_2$ molecule is smaller than the that of two two isolated hydrogen atoms and that is why two $H$ atoms try to form a covalent bond. According to the classical…
SRS
- 26,333
70
votes
8 answers
Is there an equation for the strong nuclear force?
The equation describing the force due to gravity is $$F = G \frac{m_1 m_2}{r^2}.$$ Similarly the force due to the electrostatic force is $$F = k \frac{q_1 q_2}{r^2}.$$
Is there a similar equation that describes the force due to the strong nuclear…
ergodicsum
- 829
70
votes
8 answers
Why doesn't the frequency of light change during refraction?
When light passes from one medium to another its velocity and wavelength change. Why doesn't frequency change in this phenomenon?
Self-Made Man
- 1,945
70
votes
6 answers
Why isn't my calculation that we should be able to see the sun well beyond the observable universe valid?
I recently read an interesting article that states that a human being can perceive a flash of as few as 5 or so photons, and the human eye itself can perceive even a single photon. The brain will filter this out, however.
I wanted to calculate how…
Reggie Simmons
- 691