# What is Rotating: Definition and 1000 Discussions

A rotation is a circular movement of an object around a center (or point) of rotation. The geometric plane along which the rotation occurs is called the rotation plane, and the imaginary line extending from the center and perpendicular to the rotation plane is called the rotation axis ( AK-seez). A three-dimensional object can always be rotated about an infinite number of rotation axes.
If the rotation axis passes internally through the body's own center of mass, then the body is said to be autorotating or spinning, and the surface intersection of the axis can be called a pole. A rotation around a completely external axis, e.g. the planet Earth around the Sun, is called revolving or orbiting, typically when it is produced by gravity, and the ends of the rotation axis can be called the orbital poles.

View More On Wikipedia.org
1. ### emf in coil rotating inside magnetic field

My answer is (B) but the answer key is (A). My working: $$\varepsilon=-\frac{d\phi}{dt}$$ $$=-AB\frac{cos\omega t}{dt}$$ $$=AB\omega \sin \omega t$$ Why the answer is zero? I thought the flux will be zero, not the emf. Thanks
2. ### Calculate the magnetic moment of a rotating sphere

Ich wäre Ihnen sehr dankbar, wenn Sie sich meine Lösung der folgenden Übung ansehen: A sphere with radius ##R ## is spatially homogeneously loaded and rotates with constant angular velocity ##\vec{ \omega}## around the ##z ## axis running through the center of the sphere. Calculate the...
3. ### Does the Variable ##t## Represent Multiple Concepts in Physics Problems?

I do not know how to solve this. All I got was to exclude the speed of the ant relative to the ring from the equation for its full speed
4. ### I Hamiltonian of the bead rotating on a horizontal stick

Hi, In David Morin's "Introduction to classical mechanics", Problem 6.8, when deriving Hamiltonian of the bead rotating on a horizontal stick with constant angular speed, the Lagrangian derivative over angular speed isn't included. Why is that? Specifically, the Lagrangian takes form...
5. ### I How Is Power Calculated in a Rotating System with Variable Speed?

So I have a system in which there is a disc with a moment of inertia of 1248.68. this system can rotate this disc from zero RPMs to 36 RPMs and approximately 2 seconds. How would I go about determining how much power is exerted to do said work? Many thanks
6. ### I How do we calculate the energy we used to do something?

Usually, I like to take a physical approach to phenomena that occur in everyday life. But I feel difficult to solve problems because I don't have higher education My question stems from this question (What's the difference between running up a hill and running up an inclined treadmill?), which...
7. ### A Forces on rotating disk object

Forces on rotating disk object Hi. Is it convenient to ask following question. Suppose we have solid circular object and 5 different moments like in the picture:In moment 1 we apply force (downwars direction) so as to start rotating the object around center of the mass (green dot) , Only...
8. ### Circular Motion: A coin on a rotating disk

I believe I've solved this problem, however, I got through it pretty quickly and since it's the last problem on the assignment, I feel that I may have had an oversight. For part a, I got: fs=md(α^2)(t^2) and for part b, I got: ω=Sqrt((µs*g)/d) Could someone confirm my answers? I've attached a...
9. ### Circular Motion - Newton's Second Law: Bead on a Rotating Hoop

For whatever reason, I'm having a hard time conceptualizing this problem. I understand that the tangential components of all forces involved need to cancel out in order for the bead to be stationary. I also understand that there is a mgsinθ in the negative θ-hat direction. What I don't...
10. ### I Question about a Rotating system with mass moving inwards

Dear People, I have a question. I have a rotating tube like a line that has two end and one of them is the center of rotation (like a watch arrow just tube), and inside the tube a mass that is moving towards the center of rotation. So the masses moving along the line aka along the length of the...
11. ### Kinetic energy transfer from a rotating body in an inelastic collision

The cylinder in question would have a moment of inertia of ~1.67kg*m² and rotational KE of 2.058J. At the point of impact also, assuming the body hits the sphere at a 90deg angle after traversing 90deg of displacement, it should(?) exert a force of 1.31N - enough to give an acceleration of...
12. ### I Kerr & Nordström Black Hole Evaporation: Q&A

When a Kerr black hole evaporates, what will the Kerr parameter do? Stay constant at initial value? Approach zero? Approach unity? Approach a target value somewhere between zero and unity? Also, Nordström black holes in practice (with matter around) would have a strong tendency to attract...
13. ### Calculate the induced EMF of a rotating loop

there are a bunch of problems in this section that ask similar questions, but they ask the amplitude and this doesn't. this is an even problem so i do not have the answer, but my hunch is that it is not an amplitude question. i solved for the amplitude so i am guessing i got this one wrong...
14. ### B Confusing diagram of a rotating coil in a magnetic field

Hello all, I am currently studying for a physics a-level qualification in the UK, I use the AQA specification and I am having trouble understanding this image representing a scenario I found in my textbook. The first image in the three part diagram shows this rotating coil and to me, it makes...
15. ### Rigid Body Problem Involving a Tilted Rotating Disc

Using these equations, I find L=0.02Nms, I=0.02Kgm^2 and KE=10mJ However, i don't think that this is the right method here.
16. ### Acrylic (PMMA) rotating disc tensile strength calculation

Hey folks, I've been looking around but can't piece this together as there are more than one equation and variable to take into account. My situation - I have a pmma material disc on an axis , the center hole (axis hole) is 20mm wide so a radius of 10mm, while the outer edge is at a radius of...
17. ### I Electric field in a rotating frame

Hello! I have a radially pointing electric field i.e. at a given radius, R, the electric field has the same magnitude and points radially around that circle of radius R. I have a particle moving around that circle of radius R, with uniform velocity (ignore for now how it gets to move like that)...
18. ### Coordinates of a point on a rotating wheel

My issue is in deriving the coordinates of a point on a wheel that rotates without slipping. In Morin's solution he says that: My attempt at rederiving his equation: I do not understand how the triangle on the bottom with sides indicated in green is the same as the triangle on top that is...
19. ### Rotating Rod in Plane: Kinetic Energy & Moment of Inertia

hello guys, I wanted to ask whether I can just consider/think about this as being rotation around a fixed axis in a plane representing it as if it was 'just' a rod. This is mainly so that for the kinetic energy in the second position is where if we think about it in just a plane. Is this...
20. ### A Did rotating polarizer show violations of Bell's Inequality?

The Bell inequality requires three conditions, A, B and C that can have two values (pass or fail, say). In the Aspect experiment A defines a plane, B a plane of A rotated by 22.5 degrees, while C is A rotated by 45 degrees. We take joint probabilities, and two are A+.B-, and B+.C-, and from the...
21. ### A Induced dipole moment (adiabatic) following the rotating E-field

Hello! Assume I have a 2 level system, where the 2 levels have opposite parity. If I apply an electric field, I will get an induced dipole moment. For now I want to keep it general, so the induced dipole moment can be very large, too. Let's say that I start rotating this electric field in the...
22. ### Two masses on a rotating platform

I'm having some trouble figuring this problem out. I've found the tension in (a) but I don't know where to start with (b). I've found that the distance between one of the masses and the rotational axis on the picture is R+0.52 m and that the masses rise to a height of h = 0.3 m. The moment of...
23. ### Rotating Detonation Engine, the future of aviation propulsion?

Hello everyone, I am Abheer and I am a high school student. Few days back I saw an article about RDEs (Rotating Detonation Engines). The article said it is the future of aviation propulsion. I want to ask, is it really so that RDEs are future or the low/high bypass turbofan engines will continue...
24. ### I How does a rotating magnet create levitation?

Is any physical explanation of this effect?
25. ### I Air friction in rotating ring magnet

As can be seen below we have 3 ring magnets. The middel one floats in between the other two. We want to know how to calculate the air friction of the middle ring magnet if this rotates.
26. ### I Required Strength of a Strap connecting 2 Rolls

Hello, I am trying to figure the strength (in lbs) of a strap needed to attach 2 Rolls together without breaking. Each wheel has a weight of 1000lbs and a diameter of 30in. If there is required information missing, let me know.
27. ### Number of Decks on a Rotating Habitat

My current spaceship design with several ring habitats (6 in my case) works well for worldbuilding purposes, in the sense that the reader should easily be able to tell what types of facilities can be found where on the ship. That’s because the rings distinguish themselves from each other by...

48. ### Engineering Why are the radial and the axial stress in a rotating thin ring null?

Greetings, while studying the stress in the rotating thing ring and find out the last equation that says I would like to understand why? Thank you!
49. ### Engineering Spectrum analysis of unbalanced rotating rotor

Spectrum of acceleration vs frequency Results of balanced condition Results of unbalanced condition
50. ### Disk with rod attached rotating about the center of the disk

1) Since the rod is uniform, with mass m and length l, it has a linear mass density of ##\lambda=\frac{m}{l}##, so ##I_{rod_O}=\int_{x=r}^{x=r+l}x^2 \lambda dx=\frac{\lambda}{3}[(r+l)^3-r^3]=\frac{\lambda r^3}{3}[(1+\frac{l}{r})^3-1]=\frac{1}{3}mr^2[3+\frac{3l}{r}+\frac{l^2}{r^2}].##...