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. Y

    Thin rotating disc under constant acceleration.

    In a different thread the Herglotz Noether theorem was brought up and it was mentioned that this theory implies it is impossible for a cylinder rotating about its vertical axis to remain Born rigid in a gravitational field even at constant altitude. This is an extension of the claim that a Born...
  2. T

    Calculating the Angular velocity and momentum of a rotating cuboid

    Homework Statement A concrete block is a uniformly dense cuboid of dimensions 40 x 20 x 10 cm, with mass M. It is constrained to rotate about an axis passing through two opposite corners and its centre of mass, with constant angular speed ω. Calculate the direction of the angular...
  3. Y

    Tall rotating cylinder near a black hole

    Imagine we have a very tall vertical cylinder like a very elongated telegraph pole, that is rotating at 200 rpm about its long axis on near perfect bearings. Initially the cylinder is sufficiently far from a black hole, that differences in gravitational time dilation between the top and bottom...
  4. Philosophaie

    Non-rotating or rotating Metric

    Is the Milky Way Galaxy non-rotating or rotating? Which metric is best suited: Schwarzschild or the Kerr Metric, respectively?
  5. R

    Motor: rotating blades in opposite directions?

    I'm asking myself how can I achieve the next solution: I've a plastic case with the shape like a box, where I've 2 blades: one in the front and the second in the other. My question is how can I rotate the disks in the different direction: one clockwise and the other counter-clockwise. What...
  6. S

    Understanding the Increase in Rotation Speed of a Coin on a Table

    Why the speed of the coin rotating in a table increases when it begins to stop ?
  7. D

    Shear Stress between Two Rotating Discs

    Hey everyone, As part of my PhD project I'm trying to design a small bioreactor in which I will be growing animal cells. This bioreactor will basically consist of a hollow cylindrical vessel that has an impeller in it which will keep the liquid medium in the vessel well mixed. The impeller I am...
  8. L

    A gyroscopic rotating magnetic field

    I may be on the wrong page but I had a question. You see, I do not have your math skills so I am stuck with an idea, and I have no way of finding out if I am on the right track. Question: "Can a gyroscopic rotating magnetic field render inertia mute?"
  9. 7

    Complex problem from crystallography - rotating the crystal

    The problem statement: What I have managed to do: This problem seems a bit tricky at first because it is talking about rotating a crystal while also changing the voltage - changing two variables at the same time makes no sense to me. This is why I assumed that while we change the voltage...
  10. A

    Do rotating frames have planes of simultaneity?

    It's a pretty straight-forward question, and it got me confused since most articles on the internet mention planes of simultaneity in the context of inertial frames. So if rotating frames also have planes of simultaneity, what SR says about it and how does it differ from the planes of...
  11. L

    Weight of Fast Rotating Gyro - Does Angular Velocity Increase Weight?

    there is a gyro... put it on an electronic scales which has a smooth surface...it shows the weight is M. then, let it rotate... keep increasing the angular velocity... will the weight display increase? or else?
  12. siddharth23

    Tension in different parts of a rod pivoted at1 end & rotating in HP

    I read that if a bar is pivoted at one end and is rotating in a horizontal plane, the tension at a specific point decreases as you go away from the pivoted end. Only inference I could draw from this is that the centrifugal force, which is the cause of tension, increses as you go towards the...
  13. W

    Friction of a rotating wheel on non-uniform terrain

    I have a conceptual issue with wheel friction that has been bothering me for a while. Consider the wheels on a car set to cruise control such that they rotate with constant angular velocity. Neither the wheel nor the ground are deformable (so we can ignore rolling friction) and the wheels slip...
  14. C

    Attempting to create a self rotating magnetic bike

    Hi all, new on here so thanks in advance for your responce's I am an avid cyclist and competant engineer, i dislike oil and gas so much i do not own a car. I cycle everywhere. I am tired of wanting to go long distances without assistance or a high top speed. I want to build a cycle with...
  15. E

    A cylinder rotating in Cartesian coordinate system

    Homework Statement In Cartesian coordinaate system, we describe the rotation of a cylinder. The axis of the cylinder has the same direction as the basis vector e3. Angular velocity is described by vector w = 2e1 - 5e2 + 7e3 rad/s. I must find the velocity vector (v) of a point P that is...
  16. F

    Blocks on a rotating disc connected by a spring

    To understand centripetal force due to friction better, I came up with this problem. I'm not entirely sure of my solution, though, so I'd be glad if someone else took it up too and suggested a way to work it out: Two identical blocks, each of mass m, connected by a spring of spring constant k...
  17. K

    Relativity in a Rotating Space Station

    A common solution to the problem of artificial gravity in space is to have the spaceship or station rotate, and the centrifugal force would "pull" objects toward the outside. What I haven't seen considered is that the station would have to have some kind of central motor attached to a central...
  18. haael

    Transforming coordinate system into a rotating one

    I want to solve a following problem. Imagine a collection of massive points. Each point has mass, position, velocity, moment of inertia, orientation and spin. We can calculate its total center of mass, total momentum and total angular momentum. The task is to transform the coordinate system...
  19. S

    Rotational Intertia of a rotating Space Station

    Homework Statement Four rockets attached to a (wheel) space station exert a force of 65.5N to rotate it . The space station's angular velocity is increased at a constant acceleration of 3.63 x 10-3 rads-2. Each rocket is 11.2m away from the centre. Calculate the rotational inertia of the...
  20. A

    Magnetic Flux of a partially rotating loop

    Homework Statement r=0.10 m B=0.65 T Homework Equations ampere's law? The Attempt at a Solution
  21. Y

    Coordinates transformation by rotating at the origin.

    I want to transform from rectangular coordinates ( xyz) to (x",y",z") rectangular coordinates that is rotated at the origin as show in the attachment. Then I want to transform (x",y",z") rectangular coordinates into Spherical coordinates. Attach is the method I use, I want to verify I am doing...
  22. J

    How can we tell if the universe is rotating?

    How can we tell whether the universe is rotating or not? Have we made a definitive determination yet? How does the notion of a rotating universe even have any meaning? What would a rotating universe be rotating in reference to? And lastly, if the universe were somehow rotating, would it...
  23. A

    Induced EMF in Rotating Magnetic Field with B=0.5B0z^

    A magnetic field of B=0.5B0z^ is present when a loop with radius r is rotated around the y-axis with angular velocity of w=9 rad/s. What is the induced emf? Well: flux = SB*dA = SBdAcosq(t) = Bcosq(t)SdA = 0.5B0*pi*r^2cosq(t) d(flux)/dt = 0.5B0*pi*r^2*-sinq(t)*dq(t)/dt =...
  24. R

    MHB Find the volume of the solid obtained by rotating the area?

    1.Determine the volume of the solid obtained by rotating the area between the x-axis and the graph of the function given by f(x) = cos(x^2) with x between (pi/2)^0.5 and (3pi/2)^0.5 ,about the y-axis. 2.What is the volume if the above area is rotated about the line given by x=4. Thank you in...
  25. G

    Faraday's law on rotating disk

    Homework Statement A metal disk is rotating with constant angular velocity in a constant magnetic field perpendicular to it. Use Faraday's law to fint the the induced voltage difference between the two points on the wire. The attempt at a solution So to use Faraday's Law, I need to...
  26. D

    At what frequency does the rotating mirror need to turn?

    A rotating mirror with 16 sides was used to measure the tine it took light to travel 3.5km to a concave mirror and back. At what frequency did the rotating mirror need to turn to make 1/16th of a rotation in the time it took light to travel to 3.5km and back again? im having a bit of...
  27. I

    Thomas Precession, Angular Momentum, and Rotating Reference Frames

    If any of you have the Third Edition of Classical Electrodynamics by John David Jackson, turn to section 11.8, as that's where I'm getting all this from. If not, you should still be able to follow along. In said section, Jackson gives us this equation that relates any physical vector G in a...
  28. mesa

    Rotating electron as a dipole is this right?

    An electron as shown by the Stern Gerlach experiment behaves like a dipole (albeit only in one of two states). I have been trying to figure out how this is so and drew up the following sketches. A few assumptions were made about electrons such as 'distribution' of charge assuming static...
  29. E

    Net Power In a Charged Rotating Cylinder

    Homework Statement A long hollow nonconducting cylinder (radius R= 0.060 m, length L= 0.70 m) carries a uniform charge per unit area of σ= 4.0 C/m^2 on its surface. Beginning from rest, an externally applied torque causes the cylinder to rotate at constant acceleration α= 40 rad/s^2 about the...
  30. S

    Calculating Relativistic Mass of Rotating Object

    Hi. I need to find the mass (relativistic mass?) Of an object in rotation. Say I have a string with a small rock tied to the end. The relevant variables are: A) The circumference of the weights path. B) The weight of the rock itself. C) The revolutions per minute that B...
  31. S

    Calculate angular velocity and angular acceleration of a rotating mass

    I need to calculate the angular velocity of a 2kg mass rotating in a horizontal circle of 2m radius where 1 revolution takes 4 seconds ω=v/r My attempt was this : 4/360=.0111111×57.3=.636rs.
  32. E

    Rotating disk/ sphere and moving mass along it

    Coriolis effect - In a non-friction system, f I roll something along the surface of the planet from on of the poles to the equator, it will appear to move to the west, it will essentially stay behind the planets rotation and actually rotate it in the opposite direction. Now, if we add friction...
  33. B

    Out of balance rotating system

    Figure Q4. illustrates a rotor assembly with out-of-balance rotor discs in planes A, B and C. The out-of-balance mass x radius products in planes A and C are as indicated in the figure. The out-of-balance mBrB in plane B and its angular position \ThetaB are such that the system is in static...
  34. DiracPool

    Angular momentum in a half rotating body

    If we look at the classical formula for the conservation of angular momentum, L=mvr, we can easily see that, if the radius of a rotating body is shortened, its velocity must increase in order to conserve L, and vice-versa. Again, the classical conception we have of this formula is its...
  35. N

    Ball rotating on axle which is rotating itself

    Homework Statement A ball of mass m is attached via a rod of length x to an axle that rotates with angular velocity ω. You can consider the ball to be a point mass. m = 5 kg, x = 0.3 m, y = 0.4 m, ω= 30 rad/s (a) What is the linear momentum (direction and magnitude) of the ball? (b) What...
  36. A

    Apparent weight / Rotating coordinate system

    Homework Statement Show that, owing to the rotation of the Earth on its axis, the apparent weight of an object of mass m at latitude λ is : m((g-ω^{2}Rcos^{2}λ)^{2}-(ω^{2}Rcosλsinλ)^{2})^{1/2} where ω is the angular velocity of the Earth and R its radius. The first space travellers to reach...
  37. R

    Rotating disk dropped onto another rotating disk

    Homework Statement A wheel, mounted on a vertical shaft of negligible rotational inertia, is rotating at 500 rpm (CCW from above). Part a) asks to find the new angular velocity if an identical wheel is dropped onto the shaft. I got this part right. Part b) is: Now suppose the dropped wheel...
  38. E

    Rotating diatomic - Pretty basic first year question. Workings given

    Part v is where I'm stuck. All relevant equations and the bit where I'm stuck are in the second attachment with my workings
  39. S

    Kinetic Energy of a Rotating Bar

    Homework Statement A thin and uniform bar has a length of 2.00 m and weighs 12.0 kg. It is rotating from one end on a pivot 5 times every three seconds. What is its kinetic energy? This is its hint: break the bar up into infinitesimal segments of mass dm and integrate to add up the...
  40. S

    Magnetic Moment of a Charged, Rotating Sphere Problem

    Homework Statement Show for a solid spherical ball of mass m rotating about an axis through its center with a charge q uniformly distributed on the surface of the ball that the magnetic moment μ is related to the angular momentum L by the relation μ=(5q/6mc)L Homework Equations μ=IA/c...
  41. M

    Mass moving on hoop (with hoop itself rotating)

    Homework Statement Homework Equations \frac{\partial\mathcal{L} }{\partial q} = \frac{d}{dt} \frac{\partial \mathcal{L}}{\partial \dot{q}} \cos (\alpha - \beta) = cos(\alpha)cos(\beta) + sin(\alpha)sin(\beta) The Attempt at a Solution The position of the center is...
  42. S

    Angular momentum of the EM field of rotating sphere

    The angular momentum of the electromagnetic field is defined as, $$ \vec{L_{em}} = \int \vec{l_{em}} d^3r. $$ To solve this for a rotating sphere I must consider the cases where r < R and r > R. When I did this problem I thought that there would be two solutions, one for both cases; however...
  43. A

    Acceleration in rotating frame understanding

    Homework Statement Not a homework problem but: I am revising rotating frames of reference right now and I know that: a_{inertial}=(\frac{dv}{dt}_{inertial})_{rot}+(w x v_{inertial}) But I cannot seem to understand what (\frac{dv}{dt}_{inertial})_{rot} means; more so the 'rotational' bit...
  44. S

    Frictionless ball in a rotating reference frame.

    Homework Statement Imagine that a circular disc is rotating with a frictionless ball on it( ball is not at center of the disc) If we observe the motion of the ball from the rotating frame of reference, then how can we describe its motion? Homework Equations The Attempt at a...
  45. Q

    Object flying off a rotating disc

    Why does an object on a rotating disc fly off the disc as the speed of rotation is increased? To accelerate, the object must experience a net force in the direction of acceleration -- in this case, away from the disc, perpendicular to the object's velocity vector. But what is this force...
  46. B

    Fictitious forces in rotating frames of reference

    I got stuck going over the derivation of fictitious forces in rotating frames. see specifically http://en.wikipedia.org/wiki/Rotating_reference_frame#Time_derivatives_in_the_two_frames this page to see the proof I'm talking about (sorry i'd love to be able to explain it by myself but...
  47. 1

    Torque calculation of a gate rotating around its pier

    Hey guys, I am new to this forum, I have a problem and I can't get my head around it. so basically, I have a gate that rotates in water about a pier located in the middle (the gate is is 20 m length from the middle pier on both sides, so total length is 40 m). how do i calculate the force...
  48. N

    Determine the Velocity and Acceleration of the Rotating Rod

    Homework Statement The body is formed of slender rod and rotates about a fixed axis through point O with the indicated angular properties. If ω = 4.6 rad/s and α = 4.4 rad/s2, determine the instantaneous velocity and acceleration of point A. I have attached an image of the question Homework...
  49. sergiokapone

    Rolling Dynamics of a Rotating Cylinder on an Inclined Plane

    Homework Statement Rotating with angular velocity ##ω_0## solid homogeneous cylinder of radius ##r## placed without starting forward speed at the bottom of the inclined plane, forming an angle ##\alpha## with the horizontal plane, and starts to roll in up. Determine the time during which the...
  50. N

    Motion of a ball along a groove on a rotating disk

    Will a ball placed tightly (radius of ball=width of groove) in a groove(length of grove along radius) on a rotating disk have any motion along the groove. The frictional force is zero.
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