Circular motion about a central point or axis
Questions tagged [rotation]
1117 questions
56
votes
8 answers
Proof that the Earth rotates?
What is the proof, without leaving the Earth, and involving only basic physics, that the earth rotates around its axis?
By basic physics I mean the physics that the early physicists must've used to deduce that it rotates, not relativity.
user8721
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41
votes
4 answers
Rotate an object about the time axis
Is there a notion of rotating an object about its time axis? I'm not sure if this question totally makes sense, but it seems intuitive to me that an object with dimensions in the three spatial directions and the time dimension (so an object paired…
lanerogers
- 521
40
votes
3 answers
Why wouldn't the part of the Earth facing the Sun a half year before be facing away from it now at noon?
The Earth takes 24 hours to spin around its own axis and 365 days to spin around the Sun. So in approximately half a year the Earth will have spun around its axis 182.5 times.
Now take a look at the following picture:
Assuming that the Earth is in…
O S
- 555
39
votes
4 answers
Does the sun rotate?
As implied from the question, does the sun rotate? If so, do other stars not including the sun also rotate? Would there be any consequences if the sun and other stars didn't rotate? Me and my friends have differing views on this, and would like some…
yuritsuki
- 1,628
38
votes
8 answers
Would it matter if the Earth rotated clockwise?
In the Futurama episode "That Darn Katz!" they save the world by rotating the Earth backwards saying it shouldn't matter (which direction Earth rotates). If Earth rotated clockwise and remained in it's current counter-clockwise orbit around the Sun,…
Major Stackings
- 715
34
votes
13 answers
How can the contact point of a body rolling without slipping have zero velocity?
They say that for a rolling body, the velocity of the contact point is zero. I'm not getting this. How can it be zero when it's in continuous motion?
Ashu Aman
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33
votes
10 answers
What is the Earth truly rotating about/revolving around?
Earth rotates on its axis and revolves around the sun, the sun revolves around the galaxy, the galaxy is also moving. So Earth's net rotation as observed from a fixed inertial frame consists of all these contributions (and is rather complex).
Now a…
Man
- 1,398
31
votes
4 answers
Why doesn't the phase operator exist?
In many articles about quantum optics, the phase-number uncertainty relation $$\Delta \phi \Delta n \ge 1$$ has been mentioned and used as a heuristic argument, but they say that the phase-number uncertainty relation does not exist in a strict…
Veteran
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31
votes
5 answers
Artificial gravity on rotating spaceship?
One of the possible ways to simulate gravity in outer space is to have a rotating spaceship, so that the centrifugal force experienced provides a gravity-like force.
My question is: shouldn't this only work when our feet are touching the floor of…
SuperCiocia
- 25,602
29
votes
2 answers
In counting degrees of freedom of a linear molecule, why is rotation about the axis not counted?
I was reading about the equipartition theorem and I got the following quotations from my books:
A diatomic molecule like oxygen can rotate about two different axes. But rotation about the axis down the length of the molecule doesn't count. - Daniel…
user36790
27
votes
4 answers
Does the rotation of the earth dramatically affect airplane flight time?
Say I'm flying from Sydney, to Los Angeles (S2LA), back to Sydney (LA2S).
During S2LA, travelling with the rotation of the earth, would the flight time be longer than LA2S on account of Los Angeles turning/moving away from our position?
Or, in the…
Ben
- 1,001
26
votes
7 answers
How is it that angular velocities are vectors, while rotations aren't?
Does anyone have an intuitive explanation of why this is the case?
Casebash
- 2,804
22
votes
1 answer
Which way do spiral galaxies rotate?
Is it known whether spiral galaxies typically (or exclusively?) rotate with the arms trailing or facing?
Intuitively it feels weird to think of the arms as facing the direction of rotation, but that's silly, of course -- it seems to have its origin…
21
votes
8 answers
What is the proof that a force applied on a rigid body will cause it to rotate around its center of mass?
Say I have a rigid body in space. I've read that if I during some short time interval apply a force on the body at some point which is not in line with the center of mass, it would start rotating about an axis which is perpendicular to the force and…
Alraxite
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18
votes
2 answers
What exactly does the belt/plate trick demonstrate?
I am reasonably familiar with the math behind spinors, the fact that $SU(2)$ is the universal (double) cover of $SO(3)$, etc.
I've often seen the "belt trick" and the "plate trick" used to motivate these results, but I must admit that I've never…
tparker
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