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1500 questions
47
votes
5 answers
Why aren't there spherical galaxies?
According to the Wikipedia page on Galaxy Types, there are four main kinds of galaxies:
Spirals - as the name implies, these look like huge spinning spirals with curved "arms" branching out
Ellipticals - look like a big disk of stars and other…
haneefmubarak
- 605
47
votes
8 answers
How is it possible to accelerate a neutron?
It is possible to accelerate a charged particle in an electric field, how is it possible to accelerate a neutron? How can we control its velocity?
Clandestino
- 611
46
votes
8 answers
If I am travelling on a car at around 60 km/h, and I shine a light, does that mean that the light is travelling faster than the speed of light?
The title says it all.
If I was on a bus at 60 km/h, and I started walking on the bus at a steady pace of 5 km/h, then I'd technically be moving at 65 km/h, right?
So my son posed me an interesting question today: since light travels as fast as…
Zerium
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4 answers
Why does the air we blow/exhale out from our mouths change from hot to cold depending on the size of the opening we make with our mouth?
Why does the air we blow/exhale out from our mouths change from hot to cold depending on the size of the opening we make with our mouth?
It's not just a subtle difference, but significant in my opinion. I'm inclined to discredit the notion that it's…
John
- 581
46
votes
4 answers
Does quantum mechanics violate the equivalence principle?
I have a question about equivalence principle in quantum mechanics.
Consider a Schroedinger equation under gravitional field
$$\left[ - \frac{1}{2m_I} \nabla^2 + m_g \Phi_{\mathrm{grav}} \right]\psi = i \partial_t \psi \tag{1} $$
where $m_I$ and…
user26143
- 6,331
46
votes
6 answers
Does Heisenberg's uncertainty under time evolution always grow?
Recently there have been some interesting questions on standard QM and especially on uncertainty principle and I enjoyed reviewing these basic concepts. And I came to realize I have an interesting question of my own. I guess the answer should be…
Marek
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46
votes
4 answers
At which slope angle is a runner faster than a bicyclist?
On level terrain a bicyclist is faster than a runner.
On a steep slope a runner is faster than a bicyclist.
(That's why you see bicyclists pushing their bikes uphill.)
Can we calculate the angle where it becomes more advantageous to discard the…
summerrain
- 554
46
votes
1 answer
Resolving Conflicting Reports on Fermilab $g-2$ Results
Today it was announced that the Fermilab measurements of the muon's gyromagnetic ratio are in disagreement with the Standard Model with a statistical certainty reported at 4.2 sigma [1, 2], raising the distinct possibility that the discrepancy…
Kai
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46
votes
10 answers
Why do string instruments need hollow bodies?
My textbook states, 'The sound box has a large area, it sets a large volume of air into vibration, the frequency of which is same as that of the string. So due to resonance a loud sound is produced.'
My question is why isn't the air around the…
Hayden Soares
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votes
14 answers
Why does the speed of an object affect its path if gravity is warped spacetime?
I think I understand the idea of thinking about gravity not as a force pulling an object towards another object but instead a warping of space so that an object moving in a straight line ends up following a path that brings it closer to the object,…
Cormac Mulhall
- 569
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46
votes
6 answers
Can someone please explain magnetic vs electric fields?
I've looked through about 20 different explanations, from the most basic to the most complex, and yet I still don't understand this basic concept. Perhaps someone can help me.
I don't understand the difference between the electric and magnetic force…
user1299028
- 909
46
votes
9 answers
What will happen to a ball kept on a frictionless inclined plane?
I was wondering about this question since I learned about rolling motion in the chapter on rotational mechanics. I was unable to come to a solid conclusion due to the reasons mentioned below.
The following diagram shows a ball on a frictionless…
Vishnu
- 5,266
46
votes
5 answers
Do electrons really perform instantaneous quantum leaps?
This is not a duplicate, non of the answers gives a clear answer and most of the answers contradict.
There are so many questions about this and so many answers, but none of them says clearly if the electron's change of orbitals as per QM can be…
Árpád Szendrei
- 28,452
46
votes
2 answers
Why doesn't increasing the temperature of something like wood or paper set them on fire?
Imagine we have paper book. If we put this into a pan and increase its temperature, this book would not catch on fire. If on the other hand the book interacts with this heat source directly, it does catch fire. What is the difference between these…
M. Çağlar TUFAN
- 699
46
votes
2 answers
What happens when you put water under intense pressure?
Pretend you have an indestructible tube that cannot leak, inside which is water. Imagine that in each side of the tube, you have very powerful pistons
What would happen if you compress the water inside?
Would it turn into heat and escape the…
Kiran Kharel
- 515