# Questions tagged [rotation]

Circular motion about a central point or axis

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### Is the rotational velocity of a vortex consistent across its height?

I am trying to locate information about calculating the rotational velocity of a vortex. Is the velocity at the vertex maintained across the entire vertical height of the vortex? As the radius ...
128 views

### Rotations of spin eigenstates in QM

If you have a state $| \psi \rangle = | \uparrow \rangle$ which is the spin eignstate of the spin operator $\hat{S}_z = \frac{\hbar}{2} \hat{\sigma}_{z}$ then if you view this state as a vector in the ...
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### What sort of friction does a rolling cylinder experience?

When will static friction act on a cylinder executing pure rolling? Will it act when there is some external force (or without it) and if yes wouldn't it rather be kinetic friction? The cylinder is ...
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### Would an object floating in a spinning cylinder in empty space be pushed toward the wall of the cylinder? [duplicate]

This is a rather simple question, but it intrigues me nonetheless... If there was a ball in a hollow cylinder that was spinning (on an axis) in empty space (no noticeable gravitational effects), and ...
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### Rigid-body Rotation and Kinetic [closed]

Math and formula issue Default Kinetic energy formula My question is How did we go from 2 to 3 ? I do not understand where the: (V_cm/R^2) comes from. Please give a description, where do i fail.
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### Finding average angular velocity, getting a neg answer using my inst. vel. expression. Result ok? [closed]

I have a two part question that first asked me to find an expression for instantaneous velocity given $\theta=8.5t-15.0t^2+1.6t^4$. I found that to be $w= 8.5-30.0t+6.4t^3$. Then the next part was ...
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### Force on different points on a body not passing through the centre of mass [duplicate]

I was studying about centre of mass and I found that if the line of action of force passes through centre of mass then it will execute pure translation. Moreover acceleration of centre of mass is net ...
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### How many different axes of rotation can coexist?

I have questions about rotation. There is a sphere in space. I can apply a force to cause the sphere to rotate around a central axis. An infinite number of possible central axes can be drawn. ...
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### How do experiments prove that fermion wavefunctions really pick up a minus sign when rotated by $2\pi$?

Theoretically, after a rotation of $2\pi$, a fermion wavefunction picks up a minus sign, and it is after a rotation through $4\pi$ that it returns to its initial quantum state. Now, the wave-functions ...
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### Confusion in rotating frames [closed]

my question is,if we very slightly put a ball on smooth(frictionless) rotating disc then what would happen to ball. It will fall or not. because with respect to rotating disc the ball will be acted ...
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### Which way to rotate a coin?

The picture shows rotation of a coin in two ways along a axis passing through the centre of gravity.Which method is easier to rotate the coin?
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I'm reading Feynman's lectures and I have a question regarding volume I chapter 11. In this chapter, Feynman says that not every group of numbers is a vector. He says that if we apply an operation ...
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### Why is linear movement relative but rotation is absolute? [duplicate]

Rotation,at classical mechanics at least, is always absolute but linear movement is not. What is the reason for this distinction? I will add a second question. Why this is not the case in general ...
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### Derivation of yaw, pitch, roll equations for an accelerometer

I'm struggling to find a good resource that explains how roll, pitch, yaw angles are calculated from the X, Y, Z measurements of an accelerometer. I came across this document but the explanation on ...
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### How can I solve the moment of inertia?

The source tells me to use the formula for a ring, but it is not possible, as the portions are nearer to the axis than a normal ring. How can I find the moment of inertia?
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### Can we change one rotation mode of a disk continuously into one of the other two, keeping the angular momentum vector constant?

If we consider a disk (with a uniform mass density), we have one mode of rotation around the axis perpendicular to the disk and two modes of rotation around two axes, perpendicular to each other, as ...
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### Behaviour of a magnetic compass needle near a magnet

We all know that a magnetic compass needle when suspended by a thread and placed near a bar magnet, will rotate. However like a bar magnet, will the magnetic compass needle get attracted towards the ...
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### Kinetic energy confusion?

If I am travelling horizontally, and suddenly a magnetic force acts on me and pushes me inwards (at 90 degrees), so I will follow a circular motion. But if I take a point in the circle and draw ...
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### How to remove gravity component from accelerometer X, Y readings

So I have an accelerometer which I am wanting to use in an IMU. When the device is tilted but stationary I want the x, y values to be 0, so effectively negate the effect of gravity along the x and y ...
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### Are laws of physics (mechanics) symmetric under uniform rotation?

I'm just starting to learn about symmetry. I understand that physical laws are symmetric under translation and consequently (is it not a consequence?) under uniform velocity in a straight line. I see ...
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### Rotation inside a black hole

As far as I can see most of the questions about rotation of a black hole refer to the appearance of a hole to an outside observer. What about the region within the Schwarzschild radius? According ...
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### rotational invariance

I have been treating this Hamiltonian: $$H=v\vec{p}\vec{\sigma}+\vec{A}\vec{\sigma}$$ where $\vec{\sigma}=(\sigma_x , \sigma_y)$. It is relevant for 2D graphene quantum dots with some vector ...
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### Man rotating in space

Well I think if I were in a gravity free space and was rotating then will I be able to stop myself completely by moving my hands away from my body and hence increasing moment of inertia($I$) and ...
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### What is the size of the particles which make axis of rotation in a rotating object? [closed]

In a rotating object some particles which are not moving tend to be in a straight line "axis of rotation" and all the other particles of the object tend to be in circular motion around the axis.I want ...
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### What is the 4-dimensional matrix representation of rotation operator?

The rotation operator is $$\exp\left(-i\frac{\theta}{2}\boldsymbol{J}\cdot\hat{\boldsymbol{n}}\right).$$ If $\boldsymbol{\sigma}$ is the Pauli matrix, the operator can be written as a matrix form \...
A purely rolling wheel of radius $R$, has its ICOR at the point $P$ (as per the figure). If I calculate the centripetal force on a particle at the top most point of the rim, considering point $P$ as ...