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.

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  1. S

    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. L

    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. kanekiyura

    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. M

    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. P

    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. J

    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. S

    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. A

    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. A

    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. L

    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. KataruZ98

    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. S

    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. D

    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. Grizzly_1

    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. P

    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. A

    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. M

    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. R

    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. S

    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. Ian J Miller

    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. B

    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. R

    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. Abheer Parashar

    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. sergiokapone

    I How does a rotating magnet create levitation?

    Is any physical explanation of this effect?
  25. J

    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. A

    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. Strato Incendus

    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...
  28. LCSphysicist

    As for the webpage title, it could be: What is the Radiation of a Rotating Bar?

    Ok. I was writing a big text about it, but i will summarize it. We know that $$P = \frac{\mu \ddot{m}^2 w^4}{12 \pi c^3}$$ We know, as well, that $$\nabla \times M = 0$$. Also, $$\vec K = M \times \hat \rho = M \hat \phi$$ Total current, I = $K l = M l$. Magnetic moment, so, $$M l \pi r^2...
  29. C

    I Off center torque applied to a rotating body

    Hello everyone! So I've been studying gyroscopes, and see that a torque about the shaft alters the momentum, we can find the new momentum vector by finding the torque, multiplying by a small amount of time, and finally adding that vector to the momentum vector. This will create a precession for...
  30. Leo Liu

    "Holographic" Display with Rotating Blades

    Video: I recently happened upon this holographic display design where a number of blades with led strips affixed rotate like a fan. It quite puzzles me how this such a design achieves the desired results. I am pretty confident that they use polar coordinates when mapping the pixels, but I am...
  31. JandeWandelaar

    I Will a spherical mass be set in motion by a spherical shell rotating around it?

    In general relativity, rotation of mass gives rise to framedraging effects, just like linear motion does, because of the off-diagonal components in the mass-energy-momentum tensor. So around Bonnor beams there is framedragging, as well around a rotating mass. Now imagine a spherical rotating...
  32. lindberg

    I Applying Velocity Addition in Rotating Frame: Is It Correct?

    From the top of my head, I would say that yes, the very moment our clocks are aligned, and the two bullets are launched it is perfectly ok to use the relativistic velocity addition formula to determine the speed of the bullets from my reference frame. But the more the disk keeps rotating, the...
  33. LCSphysicist

    EMF induced in a wire loop rotating in a magnetic field

    To solve this problem, we need to evaluate the following integral: $$\epsilon = \int_{P}^{C} (\vec v \times \vec B) \vec dl$$ The main problem is, in fact, how do we arrive at it! I can't see why a Electric field arises at the configuration here. The magnetic field of the rotating sphere is...
  34. WMDhamnekar

    Angular Velocity in the Rotating systems

    Summary: Consider a body which is rotating with constant angular velocity ω about some axis passing through the origin. Assume the origin is fixed, and that we are sitting in a fixed coordinate system ##O_{xyz}## If ##\rho## is a vector of constant magnitude and constant direction in the...
  35. D

    I G-force centrifuge mounted on opposite rotating platform

    Query - does a centrifuge spinning to create X g-force, mounted on a platform that is rotating the the same rpm's the opposite direction, negate the g-force? Or does the g-force stay the same but from an outside perspective the centrifuge appears stationary?
  36. T

    B Time Dilation on Rotating Disk: Clocks on Disk Perspective

    Obviously, a third observer who is at rest with respect to the disk will see that the clock on the outside has a much faster velocity than a clock on the interior of the disk, so clearly the outside clock will show that it has measured less time. But that's one question. What about looking at...
  37. ynyin

    I Rotating Polarization with Optics: Exploring the Principle

    In optics experiments, I often see the following optics configuration to rotate the polarization of an incident linearly-polarized laser beam. The final reflected beam has its polarization rotated by 90 degrees. My question is: 1) Between the quarter plate and the mirror( reflecting surface)...
  38. N

    Rotating object using product of two quaternions

    Hello guys, I'm a newbie. So I have developped an application that rotates a cube using quaternion. The initial values of the quaternion are ( w=1.0, x=0.0, y=0.0, z=0.0). Now I want to apply two consecutive rotation using two different quaternion values: The first rotation corresponds to...
  39. J

    A curved wire rotating in and out of a magnetic field

    If I'm correct then the maximum change in magnetic flux occurs when the semi circle crosses the point at which it's plane is parallel with the magnetic field and minimal when it crosses the point at which the magnetic flux is maximum ( perpendicular with the field). I'm having trouble writing a...
  40. J

    A Mass dropped onto rotating disk

    Picture a flat disk of radius r with a radial vane. The disk is rotating at angular velocity w. Assume the vane is straight, starts at the center and ends at the perimeter of the disk. A very small round mass ( of m grams) is dropped onto the disk very near the center. The vane contacts it and...
  41. DaveC426913

    B Artificial gravity rotating on two axes

    The world building thread about a derelict spaceship got me wondering. An object can rotate on two axes simultaneously, yes? Is that stable in flat space? If so, what would occupants experience as gravity? Would it change over time?
  42. J

    Find magnetic field at center of rotating sphere

    if a sphere rotates, it's like multiple currents going around in a circle. I can find the magnetic field of each of those currents at the center point of the circle and add them together. We can integrate with respect to y and R. y ranges from 0 to 5 cm away from the center of the loop and the...
  43. D

    A classical mechanics problem involve rotating

    I came up with these: (especially not sure if second is right)
  44. N

    B Centrifugal Force on Rotating 4" tire / wheel @ 100mph

    Heya PhysicsForums! Remote Control Car toy tires and wheels. a 4" tire/wheel rotates at 8400rpm at 100mph. Am wondering how many "g's" the tire "experiences" at that rpm; I imagine it being hundreds of times (if below is accurate am WAY off with my guess) Using a centrifugal force...
  45. M

    Motor calculation for a rotating platform

    Hi! My team and i have been stuck in this school project for awhile. Been reading up a lot but can't find the answer. We have been designing and rotating platform that is able to rotate a load of 2000kg. So the rotating platform would something similar to those car turntables where there would...
  46. DaveC426913

    B Swimming pool in a rotating space station

    The Exodus thread got me thinking about swimming pools in a rotating space station. Assume two scenarios: two toroidal pools that circumscribe the station, one is continuous and one is divided into segments by barriers. (Sorry, typing on my phone is very arduous for these old thumbs, so I...
  47. A

    Find the inertia of a sphere radius R with rotating axis through the center

    $$I = \int{r^2dm}$$ $$dm = \sigma dV$$ $$dV = 4\pi r^2dr$$ $$\sigma = \frac{M}{\frac{4}{3}\pi*R^3}$$ $$I = \sigma 4 \pi \int_0^R{r^4 dr} = \frac{3*MR^2}{5},$$ which is not the correct moment of inertia of a sphere
  48. A

    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. T

    Engineering Spectrum analysis of unbalanced rotating rotor

    Spectrum of acceleration vs frequency Results of balanced condition Results of unbalanced condition
  50. L

    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}].##...