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. M

    A flywheel makes 80 radians in 4 second and is rotating with constant angular acceler

    A flywheel makes 80 radians in 4 second and is rotating with constant angular acceleration during this time . It makes 60 radians in next 4 second with constant angular velocity . Find initial angular velocity and the angular acceleration ? my answer is form this equation Q= w0t +...
  2. M

    If a body is rotating at uniform angular velocity then in t sec , the angular displac

    1 ) If a body is rotating at uniform angular velocity then in t sec , the angular displacement is ... (complete ) my answer the angular displacement is increase . 2 ) If a body is making N revolutions in one second then its angular velocity in rad/sec is my answer the angular...
  3. A

    Find area of surface obtained by rotating the curve, ?

    Find area of surface obtained by rotating the curve, URGENT? Using Simpson's rule n=10, find the area of the surface obtained by rotating the curve y=x+sqrt(x), 1 less than or equal to x less than or equal to 2, about the x-axis. Include at least five decimal places in your answer. Area = ...
  4. M

    Questions in linear motion and rotating motion

    Hi please I want from you check my answer http://store2.up-00.com/May12/Ueu86896.jpg http://store2.up-00.com/May12/fkl86896.jpg
  5. I

    Rectangular coil rotating in magnetic field

    Homework Statement A rectangular coil of 80 turns has an area of 0.01m^2. It rotates @ 3000rpm about one of its in plane axes, in a uniform magnetic field having B=1.5T. Calculate the rms voltage generated. Homework Equations 1 Tesla= 1 Weber/m^2. Change in flux of 1 Weber per second...
  6. C

    How Does a Rotating Ball Affect Force Directions in a Box?

    Hello, I have a question about force produced by rotating ball. Let's say the ball rotates clockwise. The rotating ball is attached to the rotation axis with a rigid rod. The rotating ball is placed inside of the box. The box is placed on the very sensitive scale. The box is vibrating...
  7. A

    Variation of gravity in a Rotating SpaceStation

    This is very simple question, and i just need a 2nd opinion. We have a Space Station (preferably a torus) with angular velocity ω and radius r. We have a car inside which OPPOSES the angular velocity and moves with the speed ωr . So, will the gravity felt in this car be Zero? Or will it be...
  8. H

    Rotating the coordinates to coincide the principal axes

    Dear all, We can rotate the local coordinates of the element so that the stress tensor becomes diagonal. The new coordinate system would be the principal stress axes of which are in fact the eignevectors of the stress tensor. Once we have the eigenvectors ( which are generally orthogonal)...
  9. E

    Using rotating vector to draw sine waves

    We have met the idea that a radius of a circle rotating ANTI-CLOCKWISE can be used to draw a sine wave... I get that... it is a great idea but...why does it have to be rotating anti-clockwise. That seems so un natural to me. We were told it is a convention. Does that mean it is something...
  10. A

    Rotating drum being stopped dead by a pin

    I have a drum of radius of 1.375" with a wall thickness of .3025". It is rotating about its central axis at 2000 rpm. There are 6 holes drilled into the drum radially. I have a pin that slides in and out of those holes in order to release and stop the drum. I am trying to figure out the force of...
  11. A

    Detailed Windage losses calculations, rotating electric motors.

    Hi everyone, Long time reader first time poster. A little background on myself, 4th year in the field of ME mostly in simulation and analysis (FEA). I am currently working on a project of a high speed electric motor. I am putting together all the losses from the rotating motor (Copper...
  12. M

    Inelastic collision of ball with rotating beam (juggling robot)

    Homework Statement I'm trying to build a "juggling" robot but I'm getting stuck on the dynamics of catching. The robot follows the dynamics and terminology of a similar one presented in the attached paper (equation 1). Basically, there is a circular ball flying through the air which lands (and...
  13. B

    Rotating Usage of Shoes, Backpacks, to Extend Useful Life

    Hi, All: I know very little physics and/or materials engineering. I am just trying to see if there is something to the claim that alternating the usage of , say, backpacks/ shoes , will give an overall longer total life, i.e., if I will be able to get more useful days out of 2...
  14. R

    Lift of a Rotating Cylinder in Inviscid Flow

    Hi I am wondering why a spinning cylinder will produce lift in an inviscid flow. From: http://www.grc.nasa.gov/WWW/k-12/airplane/cyl.html one of the mechanisms for lift generation was the sticking of fluid particles to the wall of the cylinder. I thought that the no slip condition only...
  15. S

    Lagrangian in rotating space without potential

    Homework Statement I want to derive the centrifugal and Coriolis forces with the Lagrangian for rotating space. The speed of an object for an outside observer is dr/dt + w x r, where r are the moving coordinates. So m/2(dr/dt + w x r)^2 is the Lagrangian. The Attempt at a Solution...
  16. R

    Spring with 2 masses rotating and vibrating

    Homework Statement Consider an object consisting of two balls connected by a spring, whose stiffness is 400N/m. The object has been thrown through the air and is rotating and vibrating as it moves. At a particular instant the spring is stretched 0.3m, and the two balls at the ends of the...
  17. S

    Can a Rotating Magnet Create a Rotating Magnetic Field?

    Hello everyone, I have a quick concept question for electrodynamics course. If a cylindrical magnet, axially magnetized, is rotated round its own central axis, axis of symmetry, will this create a rotating magnetic field in the vicinity of the magnet? what if the magnet was rotated around in...
  18. B

    Rotating mass connected to elastic spring (help needed)

    Homework Statement A mass m connected using elastic spring to the roof. the mass is rotating horizontaly. mass m= 0.6kg rate or spring constant (k) = 40 N*m-1 frequency= 1/2 sec-1 spring's equilibrium length is 0.8mThe question is: what is the length (L) of the spring while the mass...
  19. J

    Cuboid stability when rotating along different axes

    Homework Statement If we have a cuboid like this one *It won't let me upload the picture or include a link but if you Google cuboid its the first picture* We know that the mas moment of inertia through the centroid is different for each face. So the yellow has the greatest mass moment of...
  20. N

    What determines the speed of two balls on a rotating disk?

    Homework Statement Homework Equations I=mr^{2} L=ωI ω=\frac{L}{I} The Attempt at a Solution I thought that since the moment of inertia was larger for the ball on the outside its angular speed would be slower. So then it would take longer to hit the wall.
  21. 9

    Gravity of a Rotating Cylindrical Space Station: Confirmation Needed

    A cylindrical space station of radius r with thin walls and mass M rotates at angular velocity ω such that the apparent gravity on the inner surface of the cylinder is equal to g. 1) Radial spokes of negligible mass connect the cylinder to the centre of motion. An astronaut of mass m climbs a...
  22. A

    Accelerometer within a freely rotating sphere?

    Hi, Please could someone explain how they think an accelerometer would work if positioned within the center of a freely rotating sphere (e.g a kicked football)? If using triple axis accelerometer and the ball was kicked from a standstill but with no spin, I would imagine that the...
  23. W

    What techniques can be used to analyze a rod rotating about the edge of a table?

    A uniform rod of length 4x is rotating about the edge O of the table. (The rod does not fall off the table.) The centre of mass G of the rod is distance x away from O. The rod is making an angle θ with the horizontal. The only forces present are the weight W of the rod, the normal reaction N...
  24. S

    Relating radius and angular freq of an rotating object

    Homework Statement an ball of mass m is connected by a string with spring constant k, to a rotating shaft. Find a relation between the radius of the circle, and the angular frequency. Homework Equations The Attempt at a Solution Let: Natural length of spring = x0...
  25. A

    Rotating Square Loop in Constant B-field

    [SOLVED] Rotating Square Loop in Constant B-field Homework Statement Homework Equations \epsilon = - \frac{d\Phi}{dt} \Phi = BAcos(\theta) = BAcos(\omegat) d\Phi = -BA\omegasin(\omegat) The Attempt at a Solution I'm trying to study for an exam and I've got this practice...
  26. S

    Acceleration of an offset rotating point on a sphere

    Homework Statement I'm trying to sort out some equations for an academic paper I'm writing. I need to work out the acceleration of a point that rotates around another point that is moving on a sphere. In the attached figure the black dot lies on the surface of a sphere, with a fixed...
  27. R

    Velocities in inertial and rotating frames of reference

    Hi, I have a couple of questions about velocities in inertial and rotating frames of reference, related by the following equation: \mathbf{v_i} \ \stackrel{\mathrm{def}}{=}\ \frac{d\mathbf{r}}{dt} = \left( \frac{d\mathbf{r}}{dt} \right)_{\mathrm{r}} + \boldsymbol\Omega \times...
  28. C

    Induced current due to rotating coil

    I attached a problem from a practice exam. I'm stuck on part b). Part A, I'm assuming the answer is the standard equation for an infinite current sheet. How do I find induced current? I can only think of using Emf = NBA*ωsintωt Where Emf= I/R, but I don't have resistance. Only other equation I...
  29. R

    Find the Centripetal Acceleration at 2.5m from a Rotating Platform

    Homework Statement A person is on a horizontal rotating platform at a distance of 4.3 m from its centre. This preson experiences a centripetal acceleration of 56m/s^2. What is the centripetal acceleration is experienced by another person who is at a distance of 2.5 m from the centre of the...
  30. Peeter

    Solving Steady Flow b/w Rotating Cylinders

    Homework Statement Consider the steady flow between two long cylinders of radii R_1 and R_2, R_1 > R_1, rotating about their axes with angular velocities \Omega_1, \Omega_2. Look for a solution of the form, where \hat{\boldsymbol{\phi}} is a unit vector along the azimuthal direction...
  31. H

    Rotating a Curve & Line Around the X Axis: A Math Problem

    Homework Statement The curve x=y^(2) and the line x=4 is rotated about the x axis. Homework Equations pi* integral from a to b of Radius^(2) The Attempt at a Solution pi* integral from 0 to 4 of (square root of x)^(2) dx. My teacher has this answer as 8pi but I think that that...
  32. C

    Vertical speed of a point attached by two rods to a rotating hinge.

    Homework Statement Not exactly homework, but an interesting problem I found for which I have some questions about the answer. A rod of length r is rotating around a point O with constant angular velocity w. Distance r away to the right from the point O is a rail. The end of the rod with...
  33. R

    Two grids, one rotating, share equivalent x-y coordinates with different values.

    I’m a woodworker, a math idiot, my trig hasn’t improved since I flunked it 40 years ago and I need help making a Christmas toy for my grand-kids. The values that follow are arbitrary, were extracted using eng graphics software and should be solid. Problem: I have one 2D surface (that...
  34. H

    Rotating y=x^(3)+1 about x=-1 Using Washer Method

    Homework Statement y=x^(3) +1, x=1, y=1; rotated about x=-1 Homework Equations Washer Method. Pi * Integral from a to b of [Outer radius]^2-[inner radius]^2 The Attempt at a Solution I understand the shell method version but I wanted to learn the washer way for this one. Pi*...
  35. P

    Volume of solids rotating about two axises

    Homework Statement Find the volumes of the solids revolution obtained by rotating the region about the x-axis and the y-axis. y=2x-x^2, y=0 The Attempt at a Solution I know how to get the volume of a function that is rotating around one axis, but the "y=0" is confusing me. Because...
  36. K

    Velocity distribution of particles in an arbitrary-arrangement of rotating gases

    If we have a "quasi-rigid" rotating convective cell where the gas overall rotates at the same angular velocity, we could establish a non-inertial frame of reference co-rotating with this convective cell such that the particles of the gas (seen from that frame of reference) may follow a...
  37. K

    Comsol - Balancing of the rotating propeller

    Hi, I am new in comsol. I currently doing a simulation on rotating propeller. I need to obtain vibration magnitude of the rotating prop.. can anyone tell me which type of analysis and how i can get the data? I have been working on this and search over the google for past two week didnt...
  38. L

    Kinetic energy of a rotating disc

    if KE=1/2mv^2 and you have a circular object rotating, with it's mass uniformly distributed through the object (ie each part of the disc weighs the same) then obviously certain parts of the disc will be moving faster than others. therefore closer to the middle of the disc, you have more KE...
  39. X

    Calculating Average Tangential Stress for Non-Uniform Rotating Disk

    Assumed a disk loaded with external pressure Po, internal Pressure Pi and rotating at the speed ω. I'm sure that average tangential stress for uniform thickness rotating disk can be calculated using equation below : σ avg = (PiRi/Ro-Ri) - (PoRo/Ro-Ri) + (ρω^2) / 3(Ro^2+RoRi+Ri^2) Ro = outer...
  40. P

    Rotating and Nonrotating Rods Superposed

    Homework Statement A uniform disk turns at 3.7 rev/s around a frictionless spindle. A nonrotating rod, of the same mass as the disk and length equal to the disk's diameter, is dropped onto the freely spinning disk . They then both turn around the spindle with their centers superposed. What...
  41. K

    Understanding Rotational Stability of Long Axles: Theory and Analysis

    Does anyone know the theory behind rotational stability of a (long, thin) axle? I would like to know the maximum allowable rotational speed of a 5 meter long axle. I suppose its something in line with the theory of column stability, but I can't find anything about it. I have made a FEM...
  42. R

    Kinetic energy of body rotating at constant angular speed

    Homework Statement A straight wire has uniform density and total mass M. The wire is bent to form a closed loop, one section of which is a semi-circle of radius a, and the other section the diameter joining the two ends of the semicircle. The body is free to move about the midpoint O of its...
  43. F

    Electromagnetic fields of a rotating solid sphere: total charge inside

    Homework Statement A solid sphere of radius a rotates with angular velocity ω\hat{z} relative to an inertial frame K in which the sphere's center is at rest. In a frame K' located at the surface of the sphere, there is no electric field, and the magnetic field is a dipole field with M=M\hat{z}...
  44. C

    Rotating cylinder on x'-axis in S' frame. Find twist per unit length in S frame

    Homework Statement A cylinder rotating uniformly about the x' axis of S' will seem twisted when observed instantaneously in S, where it not only rotates but also travels forward. If the angular speed of the cylinder in S' is ω, prove that in S the twist per unit length is yωv/c(squared)...
  45. A

    Two layered discs rotating at relativistic angular velocities

    Hypothetically, if you had an object on top of a disc on Earth that was rotating clockwise incredibly quickly such that the object had a tangential velocity of almost c, and this disc sat on another disc rotating anticlockwise with the same angular velocity, would the object feel the effects of...
  46. T

    Rotating vectors on a unit sphere

    Hi, I want to rotate vectors through 120 and they are unit vectors so they lie on a unit spheres. So basically the tails of the vectors are at the origin and given one vector with spherical coordinates (1,θ,∅), how do I obtain the coordinates of the unit vectors that make 120 degrees with the...
  47. C

    How Does Rotating Magnetic Flux Arise from Perpendicular Alternating Fluxes?

    Homework Statement Sketch phasors for two alternating fluxes with a 90 degree phase difference. If the two fluxes are directed at right angles, show that the resultant flux rotates. Homework Equations perhpas N\Phi=BANcosθ although I don't think it's necessary The Attempt at a...
  48. B

    Motion equations of a disc rotating freely around its center (3d)

    Homework Statement The system is made of a disc the center of which is pinned to the origin (so the disc cannot translate), and some weights that can be stuck on the disc to make it tilt (weights do not translate on the disc) (see images attached). There is no friction whatsoever. The only...
  49. B

    Motion equations of a disc rotating freely around its center (3d)

    The system is made of a disc the center of which is pinned to the origin (so the disc cannot translate), and some weights that can be stuck on the disc to make it tilt (weights do not translate on the disc) (see images attached). There is no friction whatsoever. The only force is gravitational...
  50. B

    Why Does Rotating Coordinate Axes Affect Calculations?

    Homework Statement 17. xy = 2 The Attempt at a Solution Do you see that step where they do the following: √2/2 - √2/2 = my answer is 0 and they multiply that to √2/2 + √2/2 = my answer is √2 So to me the answer is 0 * √2 = 0, but the book shows that that calculation = 2, then they...
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