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.

View More On Wikipedia.org
Recent contents Top users
  1. J

    Gravitational Field of Moving, Rotating Globe: A Question

    Consider a solid globe of mass M and of of uniform density. My understanding is that its external gravitational field, in the absence of any other forces, will apply an instantaneous acceleration to any small test mass directly towards the center of the globe. Is that still true in the...
  2. G

    Angular acceleration of a rotating point mass

    Hi,first time posting here, so please be gentle... I am studying a point mass doing uniform circular motion on a horizontal frictionless table with tension in a string fixed at one end as the center. Everything is clear if center of circle is treated as center of rotation 'O' for the $$\tau = I...
  3. J

    Calculating Torque for Rotating Disk: Specs, Friction, and Weight Considerations

    Hi all, I am trying to calculate the torque required by the motor to rotate a disk at a constant speed. Specs are as follows: 1. Disk radius =80mm 2. Disk Thickness =2 mm 3. Disk Weight =50gm 4. Constant speed= 3000rpm(CONSTANT) 5. Motor friction torque= 1mNm 6. Disk position parallel...
  4. Breo

    A question about a visual effect on a rotating prism

    Hello folks, I was playing with a rectangular prism 4x4x3 (almost a cube) and I was giving him a rotating movement with the hand over the table so I could see a visual effect I have seen many times in my life and now I remembered to ask about it. So when I give to it an impulse and it start...
  5. Bendelson

    Von Braun rotating space station

    So I've been thinking about the Von Braun rotating space station model lately and I was curious about a few things. First, if someone dropped a ball in one (the ship is spinning so the centripetal force is equal to the persons weight on Earth so it creates an artificial acceleration of gravity...
  6. K

    Disk rotating in a gravitational field, like a clock

    Suppose we have a large circular disk with pegs around the perimeter, and we set the disk rotating so that one pegs passes us every second. Then, we move this disk to a gravitational field, such that one side of the disk is closer to the gravitational mass than the other. From our perspective...
  7. S

    Bowling ball sliding & rotating

    Relative equations: F_net = ma a = F_net/m f = N = _net/I Problem Statement: A spherical bowling ball with mass m = 6.50 kg and radius R = 0.680 m is thrown down the lane with an initial speed of v = 9.00 m/s. The coefficient of kinetic friction between the sliding ball and the ground is μ =...
  8. Z

    Surface Function of Tilted & Rotated Circle Around Z-Axis

    My first idea is this will result in a elliptic torus. The horizontal semi-axis a=R and the vertical semi-axis b=R*cos(beta). assuming the titled or inclined angle is beta. The distance away from the z-axisis c and it is a constant. But it looks not when I plot the surface in 3D using the...
  9. LokiReise

    A question about a rotating space structure

    So I was thinking to myself, if i had a somewhat disproportionate tripodal space structure, how would i make it rotate around a chosen point where the arms of the structure (hallways and passes most likely) converged ? TORQUE AND MOMENT OF INERTIA ! Then I thought about something else...
  10. B

    Rotating Bar in uniform B Field

    Homework Statement A 1.60 m long rod rotates about an axis through one end and perpendicular to the rod, with a rotational frequency of 6.91 radians per second. The plane of rotation of the rod is perpendicular to a uniform magnetic field of 0.30 T. Calculate the magnitude of the mf induced...
  11. A

    What is the suitable unitary operator for a rotating frame?

    Hello, I have a Hamiltonian that describes a particle in a rotating cylindrical container at angular frequency ω. In the lab frame the Hamiltonian is time-dependent and takes the form (using cylindrical coordinates) \mathcal H_o=\frac{\vec P^2}{2m}+V(r,\theta-\omega t,z), where V(r,\theta,z)...
  12. K

    A physics student is sitting on a rotating platform angular velocity question

    Homework Statement A physics student is sitting on a rotating platform. He is holding a heavy weight in each of his outstretched hands. At request of his physics instructor(!) he carries out various manoeuvres to try to change his angular velocity. Which of the following scenarios are described...
  13. L

    The moment of inertia of a rod that is rotating off the end of the rod.

    Is there a formula for the moment of inertia? A thin, uniform density rod is rotating about an axis that is off the end of the rod, so it looks a bit like this: ------- | (------- is the rod and | is the axis of rotation, so the rod is rotating out of the plane of your screen) I just have...
  14. S

    Bead sliding on a rotating rod

    Bead is at rest on a thin rod pivoted at one end. Bead is about a cm from the pivoted end of the rod. Rod now starts rotating with an uniform angular velocity w rad/sec. 1.What curve does the bead trace from the point of view of an inertial observer? Here what i think... solution of the...
  15. CitrusLime

    Calculating Angular Velocity & Acceleration of Rotating Frame-B

    Greetings all, I have been pondering this for a few days and cannot come to a conclusion. Suppose you have Frame-F with basis vectors I, J, & K. Also suppose you have Frame-B (basis vectors i, j, and k) which is rotating w.r.t. Frame-F. In such a case: i = (cos Θ)I + (sin Θ)J j = -(sin Θ)I...
  16. Feodalherren

    Faraday's Law - induced emf of a rotating loop

    Homework Statement Consider the loop in the figure below. What is the maximum induced emf in each of the following cases if A = 600 cm2, ω = 31.0 rad/s, and B = 0.490 T? Rotating about x,y,z? Homework Equations Faraday's law The Attempt at a Solution This should be relatively easy since the...
  17. _N3WTON_

    Matlab: arrays, matrices, and rotating plots

    Homework Statement Generate a triangle. For this problem, generate a triangle at a grid of points that are finely spaced in the x dimension. The triangle is defined as follows: -Side 1: y = 0 for x = 0 to 2 -Side 2: x = 0 for y = 0 to 1 -Hypotenuse: y = 1-0.5x for x = 0 to 2 Alternatively, the...
  18. L

    Normal Force at Highest Point of a Rotating Ferris Wheel

    Homework Statement A Ferris wheel has radius 5.0 m and makes one revolution every 8.0 s with uniform rotation. A person who normally weighs 670 N is sitting on one of the benches attached at the rim of the wheel. What is the apparent weight (the normal force exerted on her by the bench) of...
  19. V

    Conceptual doubt in a rotating ring

    Homework Statement A metal ring of mass m and radius R is placed on a smooth horizontal table and is set rotating about its own axis with a constant angular speed ω. What is the tension in the ring ?Homework EquationsThe Attempt at a Solution Consider a small element ds=rdθ .Tension T acts at...
  20. C

    Kinetic energy of a rotating and translating body?

    Homework Statement Not a homework or coursework question, but given the simplicity of the problem I feel that this is an appropriate subforum. Consider a person spinning a rock on a string above their head at a constant angular velocity, walking away from the observer at a constant linear...
  21. Fantini

    MHB Particles rotating about each other with uniform angular speed

    Here's the problem: Two particles of mass $m$ and $M$ undergo uniform circular motion about each other at a separation $R$ under the influence of an attractive force $F$. The angular velocity is $\omega$ radians per second. Show that $$R = \frac{F}{\omega^2} \left( \frac{1}{m} + \frac{1}{M}...
  22. T

    Confusion with the centrifugal foce and potential energy

    When we release a suspended object, we recover the potential energy due to gravity as the object travels back through the height raised. When we release an extended spring, we recover the potential energy as the object travels back through the distance stretched. But when we release a rotating...
  23. CFDFEAGURU

    ANSYS Mechanical APDL - Rotating Boundary Conditions

    All, I recently completed a project where transient thermal boundary conditions are rotated around a cylinder for a general number of revolutions. In reality, the cylinder rotated but it was much easier to rotate the thermal conditions around the model in the ANSYS environment. I used 360...
  24. michael879

    Deriving Møller's Relativistic Minimum Radius for Rotating Bodies

    Can someone either derive or point me to a derivation of Møller's formula for the relativistic minimum radius of a rotating body? I've been searching for about an hour and it's driving me crazy! The only "minimum radius" equation I've seen imposes the speed limit c on a classical rotating body...
  25. E

    Rotating a laser at Moon so that spot has v>c

    Homework Statement You shine a powerful laser onto to the surface of the Moon from Earth (Earth-Moon distance is 384,000 km or 3.84E8 m). About how fast must the laser pointer rotate (in degrees per second) for the spot on the Moon to move with velocity v>c? Does this violate Special...
  26. Z

    Investigation of a Rotating Cylinder

    Hello all, I have some confusion about rotating. The bad thing is that I don't know where the point is which my confusion starts. As I want to check also my fundamental knowledge about the topic I will ask my questions step by step to see where my problem begins. I hope you don't mind. My...
  27. T

    Equation of Motion of Mass Damper and Rotating Bar

    Homework Statement Consider the inverted pendulum system, where a uniform rigid bar of mass m and length L is elastically hinged on top of a lumped mass M. The bar is constrained by a torsional spring of coefficient kτ and the mass is constrained by a damper of coefficient c. Derive the...
  28. Alettix

    Maximum Sliding Distance in a Rotating Cone - Solving for r

    Homework Statement I have gotten the following task: "A smal object is placed in a right circular cone turned "upside-down" with an apex angle equal to 90-2α degrees. The coefficient of friction is big enough to keep the object at rest when it's placed on the inne-side of the cone. After...
  29. B

    Bending moments on a rotating body

    Homework Statement A body (let's call it a rod for simplicity) is in frictionless space, and is composed of 4 smaller sub-rods fused (cannot break) end to end. Each sub-rod has a unique mass (m1, m2, m3 and m4) and length (l1, l2, l3, and l4), but they all have the same diameter d. A force...
  30. J

    Coriolis Force & Rotating Body Problem

    Homework Statement Coriolis Force - Explain how the following situations would appear in both the inertial and non-inertial reference frames. Assume the inertial frame to be a view from above. Situation 1 - a ball is thrown from the centre of a merry-go-round which is rotating...
  31. E

    Building machine to keep ball rotating

    I need a contraption that can keep a ball spinning, smoothly, at a slow speed. If it has a variable speed control, that would be better, but minimally it would need to spin a soccer ball and take around 30 seconds to make a full rotation. The look of the device doesn't matter, just that it...
  32. R

    Derivation of the Lagrangian for Rotating Polar Coordinates

    I'm reading Leonard Susskind's The Theoretical Minimum Vol. 1. 1. The problem: I'm on the section in which he asks the readers to derive the Lagrangian for a particle on a rotating carousel in polar coordinates. 2. Relevant ideas: The same Lagrangian in Cartesian coordinates is given as...
  33. Satvik Pandey

    What Is the Minimum Velocity for a Sphere to Traverse a Grooved Disk?

    Homework Statement We have a disk of mass M and radius R placed on a horizontal plane. A cylindrical groove of radius r is made on a diameter.Now a sphere of mass m and radius r is placed in the groove at the circumference of the disk. At t=0 the whole system is rotated with an angular...
  34. S

    Derivative of a rotating unit vector

    I think this is a textbook-style question, if I am wrong, please redirect me to the forum section where I should have posted this. This is my first time here, so I am sorry if I am messing it up. Homework Statement We have an n-dimensional vector \vec{r} with a constant length \|\vec{r}\|=1...
  35. Rugile

    Rotating rod - potential difference between the ends

    Homework Statement A rod of length L and made of conducting material is attached with a smaller non-conducting rod of length l to an axle, which is rotating at constant angular velocity ω (see attachment). Find the potential difference between the ends of the rod. Of what strength magnetic...
  36. J

    Estimating Impact Force from Rotating Shaft on Collar

    Hello All, Some background information: I'm a co-op engineering student and recently my supervisor asked me to do a bit of research on a solution to a problem we had. Essentially, a cardan shaft connecting a motor and a gear box failed at a joint during operation and caused some extensive...
  37. H

    Find radial imprint on rotating disk

    This problem came up after drawing a line on the spinning rotor of a food processor. I was idly musing about relativity (parallel motion and perpendicular motion). Maybe some ancient mathematician found the solution while working clay on their potting wheel! Here it is: A flat disk rotates...
  38. Q

    Rotating eigenstates of J operator into each other?

    Homework Statement Consider the following set of eigenstates of a spin-J particle: |j,j > , ... , |j,m > , ... | j , -j > where \hbar^2 j(j+1) , \hbar m are the eigenvalues of J^2 and Jz, respectively. Is it always possible to rotate these states into each other? i.e. given |j,m> and...
  39. BrainMan

    A Spider on a rotating disk conservation of momentum

    Homework Statement A 45 rpm record in the shape of a solid disk 25 cm in diameter and mass 0.1 kg rotates about a vertical axle through its center. A 15 g spider rides along the edge of the record. Calculate the final angular speed of the record if the spider drops off without exerting a...
  40. Greg Bernhardt

    How Do Rotating Reference Frames Affect Physics Calculations?

    Definition/Summary Often in physics we need to consider frames of reference that are non-inertial (the Earth spinning on its axis for example). We must therefore see how these rotating reference frames relate to an inertial reference frame. Equations \frac{d^2\mathbf{r}}{dt^2} =...
  41. Hardik Batra

    Earth is rotating around the sun?

    Why the Earth is rotating around the sun? I know the centripetal force is required for the rotation of Earth around the sun. But initially there is required some force on Earth to rotate around the sun.
  42. J

    Finding the mass of a rotating wheel with an attached mass

    Homework Statement Find the mass, M, of a rotating wheel of radius r that has an attached mass, m, suspended by a string using conservation of energy. The mass is suspended a height, h, above the ground and it takes a time of t seconds to reach the ground.Homework Equations U_g,mass = K_f,mass...
  43. E

    Coaxial Cylinders Flow: Examining Velocity & Stress in a Rotating Fluid

    A real incompressible fluid is contained in the region between two coaxial cylinders of radii R1 and R2. The outsider cylinder rotates with angular velocity w, in stationary regime, and the flow is purely circular. Neglect the action of gravity. a) Show that vφ (azimuthal velocity component)...
  44. H

    A rotating Hot Dog about an inertial observer

    According to Einstein (e.g. in his book The Meaning of Relativity), a clock rotating about a central clock will be judged by the central clock to run slower than the central clock. This means that a signal sent by the central clock will be perceived by the rotating clock as being of a higher...
  45. D

    Rotating rubber wheels made to contact. Find final angular veloctiy

    Homework Statement A solid rubber wheel of radius R and mass M rotates with angular veloctiy \omega_0 about a frictionless pivot. A second rubber wheel of radius r and mass m, also mounted on a frictionless pivot, is brought into contact with it. What is the final angular velocity of the first...
  46. hdp12

    Angular Acceleration Caused by Axehead on a Rotating Grindstone (Disk)

    Homework Statement PROBLEM: You have a horizontal grindstone (a disk) that is mass m, has a radius r, and is turning at f in the positive direction. You then press a steel axe against the edge with a force of F in the radial direction. RANDOMIZED VARIABLES: m= 95 kg r= 0.33 m f= 92 rpm F= 25...
  47. C

    Derivation eqn motion particle rotating frame

    Homework Statement So this isn't a homework problem but I don't know where else I am supposed to post for general help. I am basically trying to understand the derivation for the equation of motion of a particle in a rotating frame. See attachment for derivation and which steps I am stuck on...
  48. L

    Rotating hoop with body fixed inside of same mass

    Homework Statement A small body A is fixed to the inside of a thin rigid hoop of radius R and mass equal to that of the body A. The hoop rolls without slipping over a horizontal plane; at the moments when the body A gets into the lower position, the center of the hoop moves with velocity v0...
  49. V

    Does a rotating point charge constitute a current ?

    Does a point charge 'q' (say an electron) moving with constant angular speed ω in a circle of radius R constitute a current ? A rotating ring of uniform charge density is treated as a current flowing in the ring . On similar lines I think a point charge q is equivalent to current given by i =...
  50. T

    Linear speed of a rotating sphere

    Homework Statement Hello everyone. Each minute, I have 3d coordinates of points at the surface of a unit sphere (with center at (0;0;0)) rotating with an axis which can (slightely?) change over time. I want to know the linear speed (s) of this sphere. I don't know how to find r at each time...
Back
Top