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1500 questions
66
votes
10 answers
Why does a free-falling body experience no force despite accelerating?
Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum.
From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational field is physically indistinguishable from floating…
AdamJames
- 763
66
votes
7 answers
Why does everything spin?
The origin of spin is some what a puzzle to me, everything spin from galaxies to planets to weather to electrons.
Where has all the angular momentum come from? Why is it so natural?
I was also thinking do photons spin? we always think of the wave as…
Ben
- 669
66
votes
6 answers
Why is jumping into water from high altitude fatal?
If I jump from an airplane straight positioned upright into the ocean, why is it the same as jumping straight on the ground?
Water is a liquid as opposed to the ground, so I would expect that by plunging straight in the water, I would enter it…
Conrad C
- 921
65
votes
17 answers
How can momentum but not energy be conserved in an inelastic collision?
In inelastic collisions, kinetic energy changes, so the velocities of the objects also change.
So how is momentum conserved in inelastic collisions?
user36604
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65
votes
3 answers
Do sunrises and sunsets look the same in a still image?
A question that popped into my head: if I see a picture of the sun close to the horizon, in an unknown place, can I know if it was taken at sunset or sunrise?
Do sunrises and sunsets look the same in a still image? Can one tell them apart?
AlonMln
- 633
65
votes
7 answers
Is Biot-Savart law obtained empirically or can it be derived?
There's already a question like this here so that my question could be considered duplicate, but I'll try to make my point clear that this is a different question.
Is there a way to derive Biot-Savart law from the Lorentz' Force law or just from…
Gold
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65
votes
6 answers
How long can you survive 1 million degrees?
I asked my Dad this once when I was about 14, and he said that no matter how short the amount of time you were exposed to such a great temperature, you would surely die. The conversation went something like:
Me: What about a millisecond?
Dad: Of…
Briguy37
- 991
65
votes
12 answers
Mathematically prove that a round wheel roll faster than a square wheel
Let's say I have these equal size objects (for now thinking in 2D) on a flat surface.
At the center of those objects I add equal positive angular torque (just enough to make the square tire to move forward).
Of course the round tire will move…
John T
- 876
65
votes
18 answers
If liquid and gas are both chaotic states of matter, what's the difference between them on the molecular level?
I'm a laywoman in physics and recently found myself pondering about the matter reflected in the title of this post.
To make my question more precise from the mathematical standpoint, let's suppose you are given a 3D image of the momentary positions…
Mitsuko
- 1,649
65
votes
6 answers
Why does the same proportion of a radioactive substance decay per time period? (half life)
Just wondering, if decay is random, why does the activity half every half life, as in, why does it have to reduce by the same proportion in the same time period?
Saharsh Aanand
- 979
65
votes
5 answers
The Sun is giving us a low entropy, not energy
While I was watching a popular science lecture on YouTube, I came across this sentence
"Sun is giving us a low entropy, not energy"
which was said by Prof. Krzysztof Meissner.
I am not a physicist, but this sounds to me like a huge leap.
I would…
janusz
- 1,013
65
votes
10 answers
What is the difference between a measurement and any other interaction in quantum mechanics?
We've learned that the wave function of a particle collapses when we measure a particle's location. If it is found, it becomes more probable to find it a again in the same area, and if not the probability to finding it in the place that was checked…
Uri
- 2,130
65
votes
3 answers
Why is the Sun almost perfectly spherical?
Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest and narrow diameters would be much less than the…
user81619
65
votes
5 answers
Why can't energy be created or destroyed?
My physics instructor told the class, when lecturing about energy, that it can't be created or destroyed. Why is that? Is there a theory or scientific evidence that proves his statement true or false? I apologize for the elementary question, but…
Dustin L.
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65
votes
3 answers
Is it possible to "see" atoms?
As per my knowledge, atoms are small beyond our imaginations. But there is an image on Wikipedia that shows silicon atoms observed at the surface of silicon carbide crystals.
The image:
How can we see these distinct atoms if they are so small?
jNerd
- 923