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. faradayscat

    Dynamics/kinematics of rotating sphere

    I'm wondering about how one would describe the dynamics of a rotating sphere. Consider this: a solid sphere of mass "m" and radius "r" is set to rotate about a tangent to its surface. If it is released from the horizontal position such that it swings like a pendulum, what would be the force...
  2. sergiokapone

    Can a rotating dielectric disc be polarized?

    Can a rotating dielectric disc be polarized? No external electric or magnetic field .
  3. C

    Torque of charged rotating disc in uniform magnetic field

    Hi, I'm having an issue with finding a starting point for the following problem. I've looked through my magnetism and electrodynamic notes but was unable to find a starting point. Could someone please help direct me on the correct path? Thank you. Homework Statement A thin circular disc of...
  4. J

    Maximum height of CM of a rotating stick

    Homework Statement [/B] A uniform stick is held horizontally and then released. At the same instant, one end is struck with a quick upwards blow. If the stick ends up horizontal when it returns to its original height, what are the possible values for the maximum height to which the center...
  5. Nathanael

    Particle free to slide along a frictionless rotating curve

    Homework Statement A particle (of mass m) is free to move along a frictionless curve y(x) which is rotating about the y-axis at a constant angular speed ω. A uniform gravitational field (of strength g) acts along the negative y direction. Find the equation of motion of the particle. (That's...
  6. A

    Sliding Rod and Rotating Disc Question

    Homework Statement A uniform rod AB of length L and mass m1 is connected by a pin joint to the center of a uniform disc of radius R and mass m2. The system is placed in a vertical plane (as shown in Figure 2) and released from rest with θ=45°. (a) Draw the free-body diagrams for the rod and the...
  7. J

    Speed of an object in a rotating frame

    Is it meaningful to measure the speed of an object in a rotating frame, and if so how do you do it in the following case? Consider a rim of circumference 100 rotating at 0.8c, both measurements with respect to the inertial lab frame. An object is at a point on the rim with a standard clock...
  8. kontejnjer

    How Does Fermi Transport Describe a Gyroscope's Motion on a Rotating Disk?

    Homework Statement Describe the motion of a gyroscope with center of mass fixed on a rotating disk in coordinates of an observer which is at rest on the disk in the absence of gravity. Homework Equations The hint given was to somehow use Fermi transport, so I'm guessing: \mathbb F_u X=\nabla_u...
  9. artriant

    Calculate Wire Tension in Zero Gravity Circle | Rotating Wire

    Hello this is my first question here :) So here is my problem: We have a circle radius 50 (m), made out of iron wire mass 5.506206591207348477884587 Kg per meter of rope. Rope diameter 11/8 inces or 3.4925cm The wire rotates with 3 rpm in zero gravity 1)How can i calculate the tension? Thx...
  10. Icaro Lorran

    Rotating the angular momentum eigenket by an arbitrary angle

    Homework Statement What is the best way to evaluate the rotation of a angular momentum eigenket (## | l,m \rangle ##) around an Cartesian axis? 2. The attempt at a solution I've tried to use the method in...
  11. Corwin_S

    What happens if I have a rotating half-wave plate?

    Hey there, What would happen if I had a half-wave plate, and I rotated it at like 1 Hz? If I stick a linear polarizer on the other end, what would my outcoming beam look like if the incoming one was natural light?
  12. Multiple_Authors

    Insights Can We Tell Whether the Universe Is Rotating? - Comments

    Multiple_Authors submitted a new PF Insights post Can We Tell Whether the Universe Is Rotating? Continue reading the Original PF Insights Post.
  13. A

    Selection of gearbox for rotating a solid shaft

    Hello Being practical I have been stuck in one question like if I have a 320 mm diameter and 805 mm long shaft which is suppose to rotate through gearbox how do I need to select a gearbox. As per I think I need to calculate the torque of shaft and find the torque of gearbox and based on that I...
  14. hackhard

    Rotation of line about rotating axis

    axis A is always normal to plane of the circle and passes thru centre of circle axis B is always parallel to plane of circle and is always parallel to y- axis of lab frame. axis B passes thru centre of the circle the infinitely long line MN always lies on the plane of the circle and passes thru...
  15. S

    Help with spring rotating around its axis of rotational symm

    Homework Statement An astronaut on a spacewalk loses her grip on a circular garter spring (pictured below). Looking at the spring she notices that it is rotating around its axis of rotational symmetry at a rate of 300 rpm. The circumference of the rotating garter spring is 1% longer than that...
  16. Coffee_

    Wavefunction in rotating frame

    Hello, I have the following problem: A system in the lab frame is described by a time dependent rotating potential ##V(\vec{r},t)##. So ##H_{lab}=\frac{\boldsymbol{p}^{2}}{2m} + V(\vec{r},t)##. My book says that the Hamiltonian in the rotating frame is given by...
  17. B

    Acceleration at the tip of a rotating flexible rod

    Hello,I have a setup which has a flexible rod that is rotated by a motor. The motor has encoder unit on it which gives the position in quad counts. This we can easily convert to degrees or radians. I have made many tests and the readings are perfect. So I used the plot of the position values and...
  18. M

    Spring mass on a rotating disc

    Homework Statement I uploaded a figure demonstrating the problem w and i are constants and disc is horizontal. Disc mass is neglected. Vibrating mass only moves along the direction of springs -only horizontally at this position- [PLAIN]http://[url=http://postimg.org/image/yxuleosq1/]...
  19. jaketsi

    How Does Angular Momentum Affect the Behavior of a Rotating Drone System?

    Hi folks!First of all, English is not my native language so I hope there is not much misleading spelling mistakes, discrepancies and inaccuracy. I’m currently working with a hobby-project of a flying drone/UAV with two adjustable angled rotors. I’m able to make it fly more or less in a way it...
  20. B

    Dynamics - Pulley System with Rotating Rod

    Homework Statement At the instant shown, the rod R is rotating about its centre of rotation with ω=3.8rad/s. mA=10kg; The pulley, with mP=8.7kg and RP=0.2m, may be modeled as a uniform disc. The rod, with mR=4.1kg and L=0.8m, may be modeled as a thin beam rotating about one end. g=9.8m/s ²...
  21. A

    Mass suspended from rotating flywheel

    Homework Statement A mass of 0.5kg is suspended from a flywheel, The mass is released from rest and falls a distance of 0.5m in 1.5s Mass of wheel = 3kg Outside radius of wheel = 300mm Radius of gyration = 212mm Homework Equations a- Linear acceleration of wheel b- Angular acceleration of...
  22. B

    Accelerometer on a rotating wheel- Net force calculation

    Homework Statement I have two analog MEMS accelerometers ADXL337, ADXL377. The ADXL337 can measure acceleration upto +/- 3g (where g = gravitational acceleration) and ADXL377 can measure upto acceleration of +/- 200g. More than this much amount of acceleration, would create noise and random...
  23. D

    Mathematical pendulum in a rotating plane

    Hello, I'm looking for information regarding this equation: or specifically in my case, when a=1:. This equation supposedly describes a mathematical pendulum in a rotating plane, however, I'm unable to find information on this specific subject. I'd really appreciate it if someone could show me...
  24. bartekac

    How does angular velocity affect the density of water in a rotating container?

    Hi, I was recently thinking about a problem which I have no idea how to solve. A full water container with volume V is hanged on a rope with length L (mass of the rope is negligible). It then starts to revolute around the point where the rope is hooked (circular motion, circle with radius L)...
  25. T

    Dangling block attached to rotating block

    I’m an applied math grad student and I wanted to check my conceptual understanding of what I thought was a basic mechanics problem. You have two blocks connected by a weightless, frictionless string passing through a tiny hole in a table. On the table, one block (mass m) rotates without friction...
  26. D

    Are Quantum Mechanics and a rotating fan comparable?

    Being a non- physicist, it is extremely difficult for me to conceptualize QM. I hope to get some definite help at this forum. QM says that the sub-atomic particles exist as both waves and particles. It is not that much difficult to conceptualize. QM also says that the sub-atomic particles can...
  27. P

    Velocity of point rotating on a wheel as the wheel moves

    Homework Statement So I have to prove that the total velocity of a particle on a wheel is Vcm+Ui=Vi where Ui is the particles velocity if the wheel's center of mass wasn't moving so just v=omega*R I'm assuming and Vcm is the velocity of the center of mass and Vi is the total velocity of the...
  28. A

    Rotating sprinkler head and torque

    Hi, can anyone tell me where this "shaft torque" is coming? What is causing this torque? Screenshot is from Fundamentals of Fluid Mechanics by Munsun. http://postimg.org/image/3zilpmzbv/ Thank you.
  29. N

    Rotating Disk in Magnetic Field

    Hi I am having a difficulty understanding how to write the circuit equation inside a disk which rotates in magnetic field. the disk is made of conductor material. the resistance of the disk is: r the answer is: ir=emf+v(a)-v(b) if someone could explain it would be great! and how do i know where...
  30. newjerseyrunner

    Coordinate translation on a rotating plane

    I have this problem where I need to convert from mouse coordinates on the screen with relative coordinates on an object that can be arbitrarily translated, scaled, and rotated around another arbitrary position. I've already normalized all of the units to be the same (pixels) but the trig is...
  31. billy_joule

    Radial Deflection of a rotating shaft

    This is a series of question that appear to become more and more vague, the last part has me stumped. 1. Homework Statement A) I have an electric motor that produces 0.4 HP of shaft power at a speed of 2800rpm. What will the gearbox speed and torque be on the output of a 1:5 (in : out)...
  32. C

    Rotating multiple objects around an axle?

    I'm looking for a way to rotate blocks. There is a single axle going through the blocks.. say there are a dozen of them. I am trying to figure out a way to rotate each block individually to one of the 4 sides based on different inputs. I am also trying to accomplish this with a single motor...
  33. K

    What's the energy of a rotating bearing?

    Homework Statement The outer ring is rotating, the inner is fixed. n is the number of balls of radius r and mass m. the outer shell has mass M. the bearing (the outer shell) rotates with angular velocity Ω. what's it's kinetic energy. Homework Equations Moment of inertia of a ball...
  34. Thom_Silva

    A Rotating motor compressing a spring

    Hello, I've recently came across this video (), where the authors use a motor to compress springs and therefore achieve locomotion. I've been thinking why is there a resulting downward net force. But i can't really figure it out. Thank you for time :) See the video from 1.16 minutes and...
  35. DrTuring

    Non-centered Rotating Arm with Hinged Weight

    Homework Statement I have a an arm with an attached hinge and weight that is rotating inside of a circle, but important the arm is not rotating about the center of the circle. The arm is spinning fast enough so that the weight is always making contact with the edge of the circle. I need to...
  36. K

    Disk falling while rotating round a point

    Homework Statement The disk of mass m and radius R is at position (a), upwards. it is free to rotate round point O on it's circumference. If falls and reaches state (b), horizontal position. What are the velocities and accelerations in position (b) Homework Equations Moment of inertia of a...
  37. B

    Mathematical modeling of the deflection of a rod

    A rod is radially mounted on a motor shaft and provided with a flat end plate. By turning movement, the end plate will touch a pointed object, and the angle turned is measured.By the torque of the motor during acceleration and deceleration, a vibration and deflection happens on the rod. The...
  38. B

    Changing an ERM (eccentric rotating mass) motor

    I'm not well versed in electrical engineering, but I was looking at this. http://www.precisionmicrodrives.com/vibrating-vibrator-vibration-motors/pager-motors-erm-motors It suits my needs for a project, but I need to modify some aspects of it. In layman's terms, can someone explain to me how I...
  39. kvyn

    How does rotating a magnet affect the magnetic field?

    I'm doing an experiment on the effect of the speed of rotation of a rare Earth magnet on the voltage generated in a solenoid coil. I was wondering, how does rotating the magnet affect the magnetic field? The experiment setup is similar to the one below:
  40. Salvador

    What Happens When a Magnet Rotates Inside a Toroidal Coil?

    there is a toroidal coil , a magnet rotates in the middle of the coil , I wonder what happens when first the magnet that rotates is a permanent magnet , second case if the magnet that rotates is a electromagnet supplied with a certain frequency AC current? I wonder what kind of output we see on...
  41. W

    Force of a bar to stop a rotating cylinder

    Hi, I'm having conceptual problems for solving this one. 1. Homework Statement I drew a picture of this problem, which should show up below. Lengths x,a and b were given in the original picture. A rotating closed cylinder is braked with a bar. Its brake shoe is pressed in respect of point B...
  42. M

    Finding Acceleration and Reaction Forces in Rotating Thin Rod on a Hinge

    Homework Statement A thin rod of mass 0.620 kg and length 1.08 m is at rest, hanging vertically from a strong, fixed hinge at its top end. Suddenly, a horizontal impulsive force (14.2 i ) N is applied to it. (a) Suppose the force acts at the bottom end of the rod. Find the acceleration of its...
  43. S

    Balancing a Rotating Shaft - Determining Masses & Positions

    Homework Statement A. A shaft 2m long rotates at 1500 revs min-1 between bearings as shown. The bearings forces of 5kN and 3kN 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 a radius of 200mm...
  44. andyrk

    Rotating Rod Tension: Variations with Rotation Angle

    Why does tension across a rod rotating horizontally vary when it is rotating about one end?
  45. fluidistic

    Radiation fields from a rotating ring with current

    Homework Statement A ring with radius R has a constant current and is rotating around a diameter with constant angular velocity omega. 1)Calculate the radiation fields far from the ring. 2)What's the direction of the polarization for an observer along the axis of rotation? 3)What are the...
  46. K

    Point rotating in a coordinate system

    The point P rotates with angle α to point P'. the coordinates of the old P are x1 and x2 and for P': x'1 and x'2. Prove that: $$x'_1=x_1\cos\alpha+x_2\sin\alpha$$ $$x'_2=x_2\cos\alpha-x_1\cos\alpha$$ I drew on the left the problem and on the right my attempt. the line OA, which is made of...
  47. D

    Calculate hold down force for rotating shaft

    I have a .850" diameter steel shaft that will have a torque of 125 ft-lbs put on it. I need to calculate how much down force I need to stop the shaft from rotating. I suppose we can assume that it will be steel on steel. Going with a coefficient of friction of about .35 I tried to calculate...
  48. O

    Rotating a mass horizontally to raise a mass vertically

    Homework Statement Hi, Suppose a mass attached to a massless string is being swung in a horizontal circle with uniform circular motion, and on the other end of the string is hanging vertically with a mass attached to it. If the mass in uniform circular motion is swung around fast enough, it...
  49. K

    Angular Velocity and Acceleration of a Rotating Rod: Homework Problem

    Homework Statement A rod of length L and mass m which is free to rotate round it's edge is held, initially, horizontally. What are: the angular velocity and acceleration at angle θ The force at the nail (the axis) Homework Equations Torque and moment of inertia: ##M=I\alpha## The Attempt at...
  50. Z

    Magnetic Field of Rotating Circular Ring

    Homework Statement Find the magnetic field at position z (z=0 in the plane of the ring) along the rotation axis for a circular ring of radius r, carrying a uniform linear charge density λ, and rotating about its axis with angular velocity ω. Homework Equations I=q/t ω=2πf f=1/period...
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