Rotating Definition and 1000 Threads

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. K

    Rod rotating, falling and hitting a mass

    Homework Statement A rod of mass M and length L is in the initial position at angle θ and pivoted at the lower end. It is released and at arriving to the equilibrium state it hits elastically a mass m that slides on a surface with the friction coefficient ##\frac{\mu}{L}x## What's the angular...
  2. andyrk

    Reason for body to slip away from centre of a rotating disc

    Why does a body kept on a rotating disc tend to slip away from the centre?
  3. R

    Rotating Wheels and Point Line-up

    Hello all, I'm trying to obtain solution(s) for problems of the following nature: To keep things simple, I begin with two wheels instead, A and B. If A has the frequency f_A, and B f_B, then the location (in terms of degrees) of each marked point is computed as follows: f_A * 360 * t % 360...
  4. DeathbyGreen

    Question of spin 1/2 particles in a rotating field

    Homework Statement So I'm given a spin 1/2 particle in a rotating magnetic field in the (x,y) direction and a constant field, B_0, in the z direction and am asked to find the S matrix describing it. Given is: B(t) = [B_1 \cos(\omega t), B_1 \sin(\omega t), B_0] Homework Equations H = \sum...
  5. K

    What is the Tension in the Wire for a Mass Pulled on a Rotating Disc?

    Homework Statement A disc of radius R and mass M lays on a smooth table. a smooth channel is carved along the diameter and on both ends there are masses m. one of the masses is attached with a wire to a small, almost weightless motor that is in the center. the other mass remains fixed in place...
  6. K

    Inclined disk rotating on the ground

    Homework Statement A disk of radius R and mass m rotates on a floor with coefficient of friction μ and makes a circle of radius r0 at constant speed v0. What is the friction force between the disk and the floor. What's the inclination angle α to the vertical. It's suggested in the question to...
  7. Adoniram

    A chain falling off a rotating disc

    Homework Statement A uniform chain of length L = πR and mass M is placed on the upper half of a uniform thin disc of radius R and mass M. The disc is placed vertically and can rotate freely about its center that is fixed in space. With a small disturbance the chain starts to fall. Find out the...
  8. K

    Calculating Angular Velocity of Beads on a Rotating Hoop

    Homework Statement A vertical hoop of mass M can rotate round the z axis without friction. 2 beads of mass m each are at the top and start sliding, one on each side. the hoop starts to rotate with angular velocity ω0. the coefficient of friction is μk=μs=μ and R is the hoop's radius. What's ω...
  9. S

    360 Degree rotating mains plug socket?

    Hello, I am wondering if anyone can provide a solution to a problem I have come across at work. I have a 360 rotating platform for photography being installed in a couple of weeks and need to a solution to providing power to the objects I put on it. To give you a bigger picture we photograph...
  10. J

    Find the components of the vector by rotating the origin

    Homework Statement Hello, I just started my summer class "Applied Linear Algebra I" Last math class of my under-grad and its been 1 year since I've last taken Calc3, so I'm trying my best to get back into the groove...anyways. Our first topic we are discussing in class is vectors. [1] This...
  11. K

    Ball Rotation on a Ball: Solving for Center of Mass Velocity

    Homework Statement A ball of mass m and radius r starts off on top of a fixed ball of radius R. it rotates down without slipping. What's the ball's center of mass velocity as a function of θ. The angular velocity is ω. Homework Equations Moment of inertia: ##I=\frac{2}{5}mr^2## Potential...
  12. federiconitidi

    Levitation/orbital speed and rotating objects

    It is known that 8000m/sec is the speed required for an object traveling parallel to the Earth's surface to orbit (i.e. so that the centripetal force counteracts the gravity force). I am now thinking to an object linked to an axis of rotation (e.g. with a 1m string) and rotating about that axis...
  13. Mentz114

    Frequency shifts in rotating frames

    After the recent discussion here about the Sagnac effect** I wanted to see if there is any frequency shift if light is sent from one point on a rotating worldline to another a small distance away. It looks like this cannot happen because ##\gamma=dt/d\tau## is the same at every point on the...
  14. Aavatar

    Magnetic Field of a rotating Cylinder

    Homework Statement .[/B] Given an infinitely long charged metal cylinder that is rotating with an angular velocity ##\omega## The charge density per unit length is ##\rho##. Find the magnetic field within the cylinder. I'm trying to solve this problem by using Ampere's Law. But couldn't reach...
  15. WannabeNewton

    Frame dragging slowly rotating shell

    I was given a problem recently that I had to solve and I haven't been able to get a fully satisfactory conceptual grasp of a certain aspect of it. Consider the slowly rotating Kerr solution ##ds^2 = -\alpha^2 dt^2 + \alpha^{-2}dr^2 + r^2d\Omega^2 - \frac{4Ma}{r}\sin^2\theta dt d\phi + O(a^2)##...
  16. I

    Calculating bend moment of a rotating cutting tool....?

    Hello - I've been trying to solve this for a little while, and feel I may not understand some core concepts required to solve the problem. If you have any ideas, please let me know! I would very much like to discuss how to solve this. I am trying to calculate the bend moment from a rotating...
  17. M

    Mechanical principles rotating systems

    Homework Statement A shaft 2 m long rotates at 1500 revs min–1 between bearings as shown in FIGURE 2. The bearings experience forces of 5 kN and 3 kN acting in the same plane as shown. A single mass is to be used to balance the shaft, so that the reactions are zero. The mass is to be placed at...
  18. R

    Lagrangian: Bead on a rotating hoop with mass

    Homework Statement 'Consider the system consisting of a bead of mass m sliding on a smooth circular wire hoop of mass 2m and radius R in a vertical plane, and the vertical plane containing the hoop is free to rotate about the vertical axis. Determine all relative equilibria of the bead.'...
  19. K

    Friction on a particle on rough horizontal rotating disc

    A particle is attached to an inextensible string. The other end of the string is attached to the centre of a rotating rough disc. The string is shorter than the radius of the disc so the particle remains on the disc and moves in uniform circular motion. I don't remember the quantities but the...
  20. K

    Pendulum involving Spring and Rotating plank

    Homework Statement [/B] In the overhead view of the figure, a long uniform rod of mass m = 0.24 kg is free to rotate in a horizontal plane about a vertical axis through its center. A spring with force constant 240 N/m is connected horizontally between one end of the rod and a fixed wall. When...
  21. W

    Angular Velocity Of A Sphere Rotating Under Gravity

    Homework Statement A solid sphere of mass m and radius a can rotate freely about a point A on its surface. The sphere is held initially at rest with the line OA through A and the centre of the sphere O horizontal and is released under gravity. Find the angular velocity of the system when OA...
  22. jonny23

    Pressure in horizontal rotating tube

    Homework Statement If there is a horizontal tube rotating on axis in horizontal plane. it is filled with an ideal gas , So which end will the pressure be higher ? the end on axis?? or the free end Homework Equations P.A= m .w^2 .r The Attempt at a Solution i think the free end should have...
  23. M

    Rotating an Array: Seeking Help with Maths Skills

    Rotate an array hi everyone I'm hoping someone maybe able to help me/ point me in the right direction with the rotation of data from an array. I'll try to keep it short but my maths skills are seriously not good due to my old age and inexperience. I maybe approaching it from the wrong angle and...
  24. Alvaro Vargas

    Torque Required for Rotating a Cylinder

    Hello everyone, I am new to this forum, and here is my first question. I need some help in a particular case regarding torques. Most of the examples given anywhere on the web and books have rotations which are affected directly by gravity like pulleys and such, but, what if I want to calculate...
  25. MaximumPhysics

    Rotating Disk and two students?

    Homework Statement Homework Equations Read below The Attempt at a Solution A) D. As the mass of the students gets further away from the axis of rotation, the rate slows down (remember the skater with arms out). B) T. No explanation currently... C) ? D) T. The students exert a force on...
  26. _N3WTON_

    Relative Motion Analysis: Acceleration of rotating disk

    Homework Statement A slotted link AC is is driven by the peg P connected to a rotating disk. Point A is fixed. Determine the link's angular velocity, \omega_{ac} and acceleration, \alpha_{ac} when the angular velocity and acceleration are \omega and \alpha , respectively. \omega = 6...
  27. andyrk

    Finding Tension in a Rotating Ring: A Constant or Changing Value?

    How do we find out the tension in a rotating ring of density ρ, radius r which is rotating with an angular velocity of ω and area of cross section A? And how do we know that this tension would be constant throughout the ring?
  28. IamDev

    Help with torque calculation of underwater rotating disk?

    Hello Guys, I have a disk of diameter of 150mm and thickness of 10mm which is rotating at the constant speed of 100rpm. The disk is inside water which is approximately 4-5 cm below the surface. Disk is horizontal (parallel to the water surface). Disk is attached with the shaft of the motor. At...
  29. K

    What Are the Cartesian Coordinates of a Rotating Pendulum?

    Homework Statement [/B] Find the Cartesian coordinates (x, y, z) of a fixed reference frame expressed in terms of the coordinates (x', y' , z) of a rotating frame, which rotates with the horizontal rod HR. Choose the x' -axis to point along the horizontal rod in the direction OA. Use this to...
  30. L

    What is the direction of friction on a plate on two rotating wheels?

    Homework Statement A uniform plate of mass M stays horizontally and symmetrically on two wheels rotating in opposite directions. The separation between the wheels is L. The friction coefficient between each wheel and the plate is N. Find the time period of oscillation of the plate if it is...
  31. H

    Angular speed of rotating hoop

    Homework Statement http://imgur.com/jcZRQdu Homework EquationsThe Attempt at a Solution So I know how to solve this with conservation of energy, but I can't seem to get the correct answer using kinematic equations. τnet = Iα = (MR2*(a/R)) -Tension = MRa Fnet = ma w-Tension = ma -Tension =...
  32. P

    Velocity diagram for a rotating blade

    Homework Statement http://postimg.org/image/5o9kcuj57/ I do not understand what the vectors W and V represent Homework EquationsThe Attempt at a Solution I know U is the tip speed velocity but I don't know about the other two
  33. P

    Force to stop a rotating object

    Homework Statement The 3.2kg , 37-cm-diameter disk in the figure is spinning at 350 rpm . How much friction force must the brake apply to the rim to bring the disk to a halt in 2.4s? Homework Equations F = m * a I = (1/2) * mass * radius2 (I probably need to use this but I can't figure...
  34. P

    Lagrangian of a 2 mass rotating rod

    Homework Statement A long light inflexible rod is free to rotate in a vertical plane about a fixed point O. A particle of mass m is fixed to the rod at a point P a distance ℓ from O. A second particle of mass m is free to move along the rod, and is attracted to the point O by an elastic force...
  35. Valerie Prowse

    Rotational energy & rotating rod

    Homework Statement Consider a uniform rod of mass 12 kg and length l.0 m. At its end, the rod is attached to a fixed, friction-free pivot. Initially the rod is balanced vertically above the pivot and begins to fall (from rest) as shown in the diagram. Determine, a. the angular acceleration of...
  36. B

    Viscous damping acting on rotating disk

    I am looking for a way to calculate the torque, hence the viscous damping coefficient per T = c*w, acting on a rotating metal disk in an oil sump. How can I go about it? Thanks! PS. I am not a ME so please forgive my ignorance.
  37. P

    Torque of a rotating disc with string

    Homework Statement A disc is on a desk, with a rotation point underneath. A string is wrapped around it, and the end of the string has a mass attached to it. The string end is put over a pulley, and when the mass is dropped it causes the disc to rotate. We are given mass of the disc (80g)...
  38. TESL@

    Rotating EM Source: Learn About Its Effects

    Hello, There is an omni-directional and coherent light source rotating at the frequency of EM waves. If you think of the wave model, there will be nothing unexpected that you can imagine the space is rotating around the source. However, if it is quantized I can't tell what happens since photons...
  39. S

    Velocity of an object Rotating in vacuum , Gravity applies

    I was wondering what might happen If we for instant, Rotated a ball around an axis in a vacuum chamber. First, If the initial speed was 20m/s would it remain like that forever, hypotheticaly saying No friction exists and that Air Resistance does not exist as the Ball rotates in vacuum. Also...
  40. I

    Rotating Disk and Time Dilation

    My question is about comparing the time dilation of a clock on a spinning disk versus a clock in the vicinity of a massive object. It seems there should be a connection between the two, because of the equivalence principle, but I'm missing something because I don't quite get the answer I would...
  41. P

    Probability distribution for a rotating gas

    Homework Statement A cylinder contains an ideal gas and rotates at angular speed w. Find the probability that a molecule is at radial position r from the axis of the cylinder. Homework Equations Boltzmann distribution, P(E)∝Ω(E)exp(-E/kT) where Ω(E) describes the degeneracy of the energy level...
  42. andyrk

    Rotating Horizontal Tube filled with ideal liquid

    A horizontally oriented tube is rotating with angular velocity ω about one end of the tube which is open. The tube has ideal liquid filled inside it as shown in the attachment. Why does there have to be a pressure difference between two points in the ideal liquid at the same horizontal level...
  43. T

    Relative angular velocity in a rotating rod

    Consider a rod AB rotating about one of it's end A with angular velocity w. Now angular velocity of each point of the rod is same i.e. w. But if we have to find the relative angular velocity of the end B w.r.t. mid point of rod, what it will be? Will it be zero because, w-w=0 or first we...
  44. G

    Rotating Drums and Sand: Finding Angular Velocities

    Homework Statement A drum of mass MA and radius a rotates freely with initial angular velocity ωA(0). A second drum with mass MB and radius b > a is mounted on the same axis and is at rest, although it is free to rotate. A thin layer of sand with mass Ms is distributed on the inner surface of...
  45. ranju

    How Does Electromagnetic Torque Develop in Rotating Electrical Machines?

    Here , I want to clear about the cause of electromagnetic or interaction torque.>! I am confused in two things.. I read that the flux produced by stator coil & rotor coil interacts , the interaction give rise to electromagnetic torque.. But how this interaction produce torque..?? Is it like...
  46. F

    Determining the tension on a rotating particle

    Homework Statement [/B] A particle of mass m slides (both sideways and radially) on a smooth frictionless horizontal table. It is attached to a cord that is being pulled downwards at a prescribed constant speed v by a force T (T may be varying) Use F=ma in polar coordinates to derive an...
  47. J

    Need suggestions on transfering compressed air to rotating object

    If you had a rotating object like a tire or barrel that you wanted to distribute compressed air to while it's rotating, what would some ways to do it? One way I'm thinking is just a tight seal at the axis, but then there would be a lot of friction. Any other ideas??
  48. K

    Calculating Torque & Power of a Rotating Disk

    Homework Statement So I am calculating torque and power for a disk of radius 0.5 m that is subjected to a force of 50 N at its periphery and is rotating at angular velocity of 100 rad/s. Find torque and power.[/B]Homework Equations Torque= radius x Force = 0.5m *50N = 25Nm Power= dW/dt=...
  49. C

    Torque needed to mantain a disk rotating

    Hello, first post! I'd apreciate some help on finding out the calculus for knowing the motor's torque needed for mantaining 2 vertical disks ø46cm, 30kg each at 300rpm, taking into acount 3 generic bearings friction that hypotetically is 0.5Nm friction torque I'm having some trouble trying to...
  50. Feodalherren

    Fluid Mechanics: Rotating cylinder viscometer

    Homework Statement Homework Equations τ = μ (du/dy) The Attempt at a Solution For part B) dM = τr dA τ = μ (rΩ/Δr) ∫ (μrΩr2πr / Δr)dr = μR4πΩ / 2Δr pretty sure that's correct. I'm confused for part A though. I want to set it up as dM = τR dA = τR (2πRdL) and τ = μ (RΩ/L)...
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