Questions tagged [rotational-dynamics]
A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.
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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 ...
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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.
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Why does a body always rotate about its center of mass? [duplicate]
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 (...
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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 ...
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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 ...
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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 ...
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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 ...
user98038
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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 ...
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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 ...
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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 ...
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Why don't helicopters use reaction wheels to counter the main rotor?
As the main title says. I'm finding myself wondering about helicopters. The tail rotor is a vulnerable and key piece of equipment, especially on military helicopters. I know some helicopters instead ...
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Does centrifugal force stiffen a rotating blade?
I'm a helicopter pilot with limited physics knowledge (units in BSc and HNCs).
I have recently challenged an assertion that rotating blades are stiffened by centrifugal force. In My mind, stiffness ...
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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 ...
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Is 13 really the answer for the "Devil's problem" in physics (a rolling tube with a rod)?
Recently I chewed the fat with a physics student and got intrigued by him mentioning "the Devil's problem," which he described as a simply worded mechanics problem that is extremely ...
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Dynamics of a rotating coin
Sometimes when I'm bored in a waiting area, I would take a coin out of my pocket and spin it on a table. I never really tried to figure out what was going on. But, recently I wondered about two things:...
user29305
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How can the Earth keep spinning with a liquid core?
In regards to the 'conservation of angular momentum' being the explanation of why celestial objects spin...
If you fill a ball or any other container with a liquid and try to spin it, you will not ...
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Could pressing the brakes on a car in mid-air affect its pitch rotation?
In a racing video game series named Trackmania, there is a game mechanic where when you hit a jump and the car is in mid-air, you can stop the car from pitching downward by tapping on the brakes.
I am ...
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Why is it easier to carry a person while spinning than not spinning?
I was carrying my friend around the other day when I was spinning her she was light but when not spinning her and just carrying her around she was heavy, why is that?
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Why do bikes hardly ever skid while braking with the front wheel?
When abruptly braking with the rear wheel on a bike, it tends to skid pretty easily. Doing the same with the front wheel is a very different experience. Instead of skidding, the bike lifts the rear ...
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Stability of rotation of a rectangular prism
I've noticed something curious about the rotation of a rectangular prism. If I take a box with height $\neq$ width $\neq$ depth and flip it into the air around different axes of rotation, some motions ...
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Can a Foucault pendulum really prove Earth is rotating?
According to this article, a Foucault pendulum proved Earth was rotating. I'm not sure it really proved it.
If Earth weren't rotating and a Foucault pendulum started in a state with zero velocity, it ...
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How does an isolated body in deep space 'know' it's rotating? [duplicate]
We can imagine an object floating in the known universe, maximally distant from any other large mass. Maybe it has been there since coalescing after the big bang.
What physical phenomena tell it ...
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Can spinning arms really help you balance on the edge of a cliff?
This is how many cartoons depict a character about to fall from the edge of a cliff. You can see movie characters do it. You can also see real people doing it. But does spinning arms like that ...
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How can earthquakes shift the earth's axis?
One often comes across news articles that claim that an earthquake shifted the earth's axis.
http://news.google.com/?q=earthquake%20shifted%20OR%20shifts%20earth%27s%20axis
If you ignore the ...
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Why don't spinning tops fall over?
One topic which was covered in university, but which I never understood, is how a spinning top "magically" resists the force of gravity. The conservation of energy explanations make sense, but I don't ...
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Can adding weight to something make it tilt slower?
Let's say we have 2 sticks, both a meter long. We put both of them on the ground vertically. To the top of one of them we attach a weight. Then we tip both of them over and let them fall.
Assume ...
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Will a falling rod stay in contact with the frictionless floor?
Question
A uniform rod of mass $M$ is placed almost vertically on a frictionless floor. Since it is not perfectly vertical, it will begin to fall down when released from rest.
I have seen solutions ...
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Is a westward flying plane heavier than an eastward one?
I understand that you weigh less at the equator due to the increased centrifugal force. From my understanding, the faster you circle the Earth, the less your effective normal force you would feel, up ...
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What causes a rotating object to rotate forever without external force—inertia, or something else?
Someone told me that it is not inertia, but I think it is inertia, because it will rotate forever. In my understanding, inertia is the constant motion of an object without external force. Am I wrong?
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Why are angles so weird?
I'm potentially asking quite a stupid set of questions here but I'm wondering if there is some overarching theory about why angles, and "rotational" quantities which deal with them, have ...
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Can a car steer on a frictionless surface?
Do the front tires of a car act like gyroscopes, such that a car could steer on a frictionless surface?
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Physical meaning of the angular momentum
Still reading Classical Mechanics by Goldstein, I'm struggling on a very basic notion: angular momentum. I physically understand it as the momentum of an object rotating around something given a ...
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Can a ultracentrifuge be used to test general relativity?
With today's ultracentrifuge technology, they can spin so fast that the sample can be subjected to accelerations of up to 2 millions Gs. That is equivalent to two solar masses. Has someone tried to ...
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Why do we assume weight acts through the center of mass?
The weight of a body acts through the center of mass of the body. If every particle of the body is attracted by earth, then why do we assume that the weight acts through the center of mass? I know ...
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The sound of rotating helicopter blades
Why do helicopter blades make this pulsing, oscilating, slapping(?) sound?
Since their movement is smooth, shouldn't the sound be a similar, constant shush, perhaps increasing or decreasing in ...
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What makes a wheel spin?
I don't fully grasp what makes a wheel much easier to move than to push a solid block.
The pressure at the point of contact between a wheel and the ground must be pretty enormous compared to the ...
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Why certain rotations are unstable? (Euler Equations)
We have the Euler equations for a rotating body as follows
$$I_1\dot\omega_1+\omega_2\omega_3(I_3-I_2)=0\\
I_2\dot\omega_2+\omega_1\omega_3(I_1-I_3)=0\\
I_3\dot\omega_3+\omega_2\omega_1(I_2-I_1)=0$$
...
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What determines the angle of the cushion on a pool table?
If you look at the cushions (bumpers) on a pool table, you'll see that they're not vertical. They're tilted inwards. About 10 years ago, I came across a physics exam in which one of the problems ...
user4552
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If I toss a coin, vertically, on the surface of Mars, will it land back in my hand?
When I toss a coin in Mars, is the planets atmosphere rare enough that I'd rotate with the planet (at its angular velocity), but not the coin?
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Why is climate change triggering faster rotation?
On July the 29th 2022, the Earth finished its rotation about 1.5 milliseconds earlier than the entire 24 hours. Scientists link this to climate change, saying that a possible reason could be due to ...
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What is the cause of rolling friction? & why is it less than sliding friction?
Rolling friction is the resistance to motion experienced by a body when it rolls upon another. It is much less than sliding friction for same pair of bodies. When one body rolls upon another, there is ...
user36790
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Why does the weighing balance restore when tilted and released
I'm talking about a Weighing Balance shown in the figure:
Press & Hold on onside of the horizontal beam and then release it. It makes some oscillations and comes back to equilibrium like shown in ...
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Rotation angle of a giant water lily when a child crawls on its rim
Below is a picture of Giant Water Lily. Scientific Name: Victoria Amazonica. Leaves of some of these could be as big as 3 m diameter and carry a weight of 45kg spread evenly and can support a child. ...
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Why does torque point perpendicular to direction of the motion?
I have an intuition problem calculating torque using the cross product formula. As for example let the magnitude of the force be 50 lbs and length of the wrench be one foot and you are exerting ...
user86411
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A rope attaches the Moon to the Earth. What happens?
Consider the Earth (mass $M$, radius $R$, rotating about its own axis at $\Omega$) and the moon (mass $m$, radius $r$, with axial rotation equal to $\omega_m$), whose centre of masses are $d$ apart. ...
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