# Questions tagged [rotation]

Circular motion about a central point or axis

658 questions
Filter by
Sorted by
Tagged with
0answers
24 views

### 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 ...
1answer
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 ...
3answers
125 views

### 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 ...
1answer
70 views

### 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 ...
1answer
209 views

### 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.
1answer
106 views

### 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 ...
2answers
1k views

### 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 ...
3answers
2k views

### 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. ...
1answer
164 views

### 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 ...
2answers
119 views

### 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 ...
1answer
70 views

### 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?
2answers
350 views

### Vector addition and translations

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 ...
0answers
73 views

### 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 ...
2answers
623 views

### 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 ...
2answers
125 views

### 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?
1answer
36 views

### 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 ...
1answer
2k views

### 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 ...
4answers
269 views

### 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 ...
2answers
11k views

### 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 ...
2answers
140 views

### 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 ...
1answer
79 views

### 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 ...
0answers
236 views

### 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 ...
2answers
115 views

### 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 ...
1answer
72 views

### 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 ...
3answers
435 views

### 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 \...
2answers
188 views

### Calculating force through ICOR (instantaneous centre of rotation)

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 ...
1answer
144 views