# Questions tagged [rotational-kinematics]

A tag for questions about rotational motion, including angular velocity and angular acceleration.

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### Isotopic separation and circular motion

I have read in a textbook of an high school (I not know) that exist a centrifuge with isotopic separation of the radioactive material very similar to the centrifuge for hematocrit to separate the ...
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### Angular velocity to linear velocity Modern Robotics textbook

In the second to last sentence, I have no idea how $v = (2,0)$ was calculated. Can someone derive this for me in detail, or with a picture?
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### Why the direction of the omega (angular velocity vector) is along the axis of rotation? Also for angular acceleration

I know that the direction of omega is taken along the axis of rotation but I don't understand it why it is taken? I also know that $\mathbf v = \mathbf ω \times \mathbf r$ so, all three vectors ...
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### In rotational motion, why $a = rα$?

The formula of torque is given by $$τ= F*r = Iα,$$ while solving some questions I came across a question of rotating pulley where these two formulas were equated to find value of $α$. How $a=rα$? a ...
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### Is it possible to find the position of spherical ball only using gyroscope raw data?

Assuming the spherical ball undergoes pure rolling and errors from gyroscope can neglected. Can I use angular velocity from gyroscope to find the position by computing rotations times its radius?
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### Difference between nutation and polar motion

If you add a mass to your spinning globe or just change the mass distribution does it increase nutation or polar motion? And How do I calculate nutation? For this I take earth as an example. from what ...
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### The Rotational kinetic energy [closed]

Earth has more kinetic energy than the cloud from which it was formed. Where did this energy come from?
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### Angular velocity or frequency in an uniform circular motion? (for students of an high school withouts the calculus)

In an uniform circular motion, we know that the angular velocity is: $$\omega=\frac{2\pi}{T}$$ and your measure is: $$[\omega]=\frac{\text{rad}}{\text{s}}$$ i.e. revolutions per second (in Italian ...
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### Weight lifted by cable wound on a cone

This problem is from Hounser & Hudson, Applied Mechanics: Dynamics (1959): The answer given by the book is: $$a = \frac{Dd \omega^2}{4 \pi h}$$ I was trying to solve it using polar coordinates (...
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### If a body is lying on a frictionless surface, and we give it an impulse, will it start rotating about its center of mass?

If not, about what point will it rotate? If we want to know about what point an object will rotate in questions like these, how do we figure it out?
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### Why is a mechanical advantage less than 1 required for class 3 levers?

From what I understand, mechanical advantage is equal to the ratio of force produced to force applied, which is equal to the ratio of effort to load and effort arm length to load arm length Therefore,...
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### How to judge direction of motion?

I have this scenario suppose a cylinder is made by joining two symmetrical cones and is given a gentle push on two rails A and B . What will be the motion of cone . Will it turn right or left I ...
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### Correct Way to Find Linear Velocities Along a Kinematic Chain

I'm following a freely available robotics course by Stanford University, which explains how to obtain linear and angular velocities along a kinematic chain. I'm specifically concerned with the case ...
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### “Kinematic” dynamics or dynamics that ape kinematic movement

This is a question related to unity's physx engine, but also a general question as well. How do you make linear and rotational dynamics work kinematicaly? For example, I add a force to an object and ...
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### Accelerometer (on a rigid-body) readings, knowing its position and attitude in an inertial frame

Good morning, I'm trying to simulate a rigid body with some accelerometers attached to it. The aim is to simulate accelerometers readings that will be later fed into a Kalman Filter (after being added ...
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### Momentum of a body with $n$ bodies inside

So, let's say that I have a big hollow ball and I put in n small balls inside it, each with a momentum m. Then, these small balls are allowed to move freely around inside the ball. What is a bound on ...
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### Rotation of cylinder inside another one. Find radius of curvature [closed]

Consider two cylinders: the first one is fixed and has a radius $R$ and another one is rotating inside the former (and has $r$: $2r > R$). Consider the moment when the small cylinder places on the ...
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### Will two masses connected by a rod sliding on a frictionless surface lift off? [closed]

Consider the following simplified model of a skater falling over: Two equal masses m are attached to opposite ends of a light, straight rod of length 2. One mass rests at (0,0) on a frictionless ...
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### Running backwards on a carousel

Let's suppose I'm on a carousel rotating with a speed $\omega$ and start running on it in the opposite direction with a speed $v$ such that $\omega r=-v$ where $r$ is the distance between me and the ...
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### Would Radio Communications Between Parties Experiencing Time Differently Be Compressed/Stretched

This is a contrived and extreme example that is likely not even possible, but I'm hoping the answer will help me understand something about communications across relative time. Imagine two individuals ...
3k views

### Why is acceleration directed inward when an object rotates in a circle?

Somebody (in a video about physics) said that acceleration goes in if you would rotate a ball on a rope around yourself. The other man (ex Navy SEAL, on YouTube too) said that obviously it goes out, ...
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### How the rotation is possible applied onto derivatives?

After reading kinematics of mobile robot or the rigid-body, I get something not quite undersand why it it possible. Suppose that coordinate system $A$ is the global or the reference frame, in which a ...
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### Angular momentum and conservation of energy when sitting on a spinning chair [duplicate]

Usually, the spinning chair problem is one of the typical angular momentum problems. And most of them start with a person holding two dumbbells on his two hands and bringing his arms in, then by ...
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### How do Roll, Pitch, and Yaw Interact?

I'm making a spaceship piloting game, and I'm trying to make the movement follow the laws of physics. The ship is able to control it's angular acceleration in pitch, yaw, and roll. The way I've ...
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### Why do rotating fidget spinners sometimes create a perception of opposite spinning?

Firstly, I apologise for asking this question as I really don't know if it's although a physicis question or not! I am sorry if that's not the case but from the very little age I(probably everyone) ...
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### When to consider rotating body as point mass?

I'm not asking you to solve this question, but here it is anyways for clarification purposes: A rod of mass $m$ and length $2R$ can rotate about an axis passing through $O$ in vertical plane. A disc ...
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### Conservation of angular momentum in rolling cones

Consider the situation shown in the figure, A cone is set rolling on a cone so there is angular momentum about the vertical and there is an instantaneous angular momentum that is consistently moving ...
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### Why does merely changing point of application of force change kinetic energy?

Consider two spheres A and B of similar mass and radius kept on a smooth surface. If I give an impulse 'J' to one of them along its centre of mass axis, it would only translate and not rotate. Its ...
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### Is there a difference in terminology between velocity vs velocity of the center of mass?

I was wondering if there was a difference between velocity of the center of mass of an object vs finding the velocity of an object in general. The case I was looking at was in a ball rolling without ...
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### Confused in Newton's second law for rotation

I'm a high school student and I am really confused about a point from rotational mechanics. My confusion is as follows- We are often taught that $\tau=dL/dt$ and $\tau=I\alpha$ are the same if the ...
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### In Uniform Circular Motion, why does the normal accelaration not change the magnitude of velocity?

According to pythagorean theorem V2 should be greater then V1.But why doesn't it happen?
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### Am I understanding the concept of rotations correctly?

Consider a ball placed at distance $r$ from an origin point $O$ on a horizontal plane and remains stationary. When the ball is viewed from a coordinate system which is rotating anticlockwise about $O$...
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### How does physics deal with perpetual motion in spins?

This is a bit a bit of a weird question. Simply put, if a body such as a planet spins, there is no internal issue (that I know of) that would cause it to eventually stop (by internal I mean that an ...
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### Does this kinematics problem involve rotational motion?

I'm given the following problem: A javelin thrower standing at rest holds the center of the javelin behind her head, then accelerates it through a distance of 70 cm as she throws. She releases the ...
Since the moment of inertia is defined as $\int r^2 dm$ where $r$ is the distance of the mass element from the axis, one can move a mass element parallel to the axis, without changing the moment of ...