A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.
Questions tagged [rotational-dynamics]
4429 questions
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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86
votes
7 answers
Why is the Earth so fat?
I made a naive calculation of the height of Earth's equatorial bulge and found that it should be about 10km. The true height is about 20km. My question is: why is there this discrepancy?
The calculation I did was to imagine placing a ball down on…
Mark Eichenlaub
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74
votes
6 answers
Is there a way for an astronaut to rotate?
We know that if an imaginary astronaut is in the intergalactic (no external forces) and has an initial velocity zero, then he has is no way to change the position of his center of mass. The law of momentum conservation says:
$$…
David
- 1,116
66
votes
10 answers
Why doesn't a bike/bicycle fall if going with a high speed?
Why does a bike/bicycle fall when its speed is very low or close to zero and is balanced when going with a high speed?
Ahmad Farid
- 777
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
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
63
votes
15 answers
Why does dust stick to rotating fan propeller?
Why does dust stick to rotating fan propeller?
Intuitively, most people (including I) think of the dust will not stick to rotating fan propellers.
Display Name
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61
votes
10 answers
Why does a body always rotate about its center of mass?
I found after searching that this question has been asked before. But all the answers were not convincing.
Suppose I have a body which is free, not constrained always rotate about its center of mass (COM). Why is that so?
A convincing answer that I…
Shashaank
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58
votes
8 answers
Principle of physics used in the lift of skateboard
What is the principle of physics used in this popular stunt?
Initially, I thought aerodynamics due to an increase in the angle of attack, but its magnitude is not sufficient to balance the whole body and skateboard. Please, can anyone help me to get…
Rajakr
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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
- 563
53
votes
12 answers
What do people actually mean by "rolling without slipping"?
I have never understood what's the meaning of the sentence "rolling without slipping". Let me explain.
I'll give an example. Yesterday my mechanics professor introduced some concepts of rotational dynamics. When he came to talk about spinning wheels…
pppqqq
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51
votes
5 answers
How do bicycle spokes work?
As you know, it is quite obvious that bicycle spokes attach the hub in the center to the rim. What else do they do? If you compare the wheels today with the ones from ancient times, there are more spokes now on motor bikes and bicycles than of a…
Vaishnavi
- 1,107
50
votes
3 answers
Why don't galaxies orbit each other?
Planets orbit around stars, satellites orbit around planets, even stars orbit each other. So the question is: Why don't galaxies orbit each other in general, as it's rarely observed? Is it considered that 'dark energy' is responsible for this…
user98038
48
votes
1 answer
Why does this object periodically turn itself?
See below gif image taken from here.
Or see this Youtube video about 30 sec in.
Is this a real effect?
Why does it seem to turn periodically?
Can it be explained by classical mechanics alone?
Is there a simple equation that models this…
pacó
- 515
48
votes
5 answers
Intuition as to why the orientation (of a 3D object) is not a conserved quantity?
Say you start off floating in space, in a fixed position and orientation,
with zero linear and angular velocity, with no external forces.
So you are a closed mechanical system. By twisting your body around,
you can't change your linear…
Don Hatch
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