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. P

    What Causes the Rod to Rotate?

    Homework Statement A vertical rod is rotating about its longitudinal axis at a constant angular velocity Ω. It is allowed to swing freely from the endpoint A. The angle between the rod and the longitudinal axis of the system is denoted by θ. Point A is located on the highest endpoint of the...
  2. C

    Rate of Change of Vector in Rotating Frame

    I recognize the rate of change of a vector in an inertial frame S can be related to the rate of change of the vector in a rotating frame S0 by the equation below taken from my textbook, where Ω is the angular velocity vector. $$\Big(\frac{dQ}{dt}\Big)_{S_{0}}= \Big(\frac{dQ}{dt}\Big)_{S} +...
  3. D

    Calculating Angular Momentum Reduction in Rotating Rockets

    how do i calculate the gradual reduction of angular momentum a rocket initially has before it fires its main rocket engines? I am assuming if the thrust is high enough then the rocket should eventually stop rotating and travel in a straight line. assume the rocket is in a universe without...
  4. Farang

    I Rotating Black Holes: Q&A with First-Time Poster

    Hi there! This has been on my mind for a while now, maybe someone here can help me understand. First of all, non-rotating black hole is an idealized concept, right? Why the term then? Other objects are not normally referred to as rotating stars, rotating planets, etc... And the main question...
  5. James Kent

    How can a device prevent twisting of USB cables when rotating?

    This is a thought experiment: My PC is mounted on my ceiling. I want to run a USB peripheral through a cylindrical retraction device (like a dog leash). The device is going to mount to the ceiling also and rotate about it's vertical axis. This will allow me to pull down the mouse from the...
  6. C

    Angular momentum: rotating ice skaters

    Homework Statement Two ice skaters of mass ##m = 50\,\mathrm{kg}## each are moving towards each other frictionless on parallel paths with a distance of ##3\,\mathrm{m}##. They both have a velocity of ##v_o=10\,\frac{\mathrm m}{\mathrm s}##. Skater 1 is holding a massless rod of length...
  7. Edward258

    Find the temperature increase of a rotating disk

    Homework Statement It's a Blackbody radiation problem: A beam of wavelength λ, in the state of right circular polarization, leads to an absorbent disk.The mass of the disk is m, it's specific heat is C, and its moment of inertia is I .The disk is initially at rest, but after a lapse of time...
  8. T

    Fields of Rotating Dielectric Sphere in Dielelectric Medium

    Homework Statement A dielectric sphere with the electric and magnetic susceptibilities ε1 and µ1 is rotating with angular frequency ω in a constant electric field E~ in a medium, characterized by the parameters ε2 and µ2. The angle between the rotation axis and the direction of E~ is α. Find...
  9. V

    I Generalized Tetrad Formalism for Rotating Spacetimes and the Equatorial Plane

    I'm interested in tetrad formalism for describing phenomenons near Kerr black hole. I've read some papers and I have a question about Localy Non-Rotating Frame (LNRF). In all papers is mentioned that most of astrophysically important cases are in equatorial plane (EP) and deals with EP only...
  10. D

    Rotating uniform rod about an arbitrary axis

    Homework Statement A thin uniform rod of length l and mass m is constrained to rotate with constant angular velocity omega about an axis passing through the center O of the rod and making an angle alpha with the rod. a) Show the the angular momentum L about O is perpendicular to the rod and is...
  11. mister mishka

    B Double slit question, rotating polarizers...

    I've wondered about this for sometime, say you rotate one of the polarizers (one of the two covering each slit) slowly from perpendicular to parallel, would the interference pattern slowly come into view?
  12. BrainMan

    Turntable Rotating on Shaft Problem

    Homework Statement Homework Equations ωf = ωo = αt ∑τ = Iα The Attempt at a Solution [/B] 1) Find the acceleration ωf = ωo + αt (ωf-ωo) / t = α = -0.231 rad/sec 2) Find ∑τ ∑τ =Iα I assumed that the only torque acting on the turntable was the torque due to friction τfriction =...
  13. VMP

    Point mass rotating about a pole with a spring

    Homework Statement In the beginning a point mass is rotating in a circle of radius L. The spring is providing the centripetal force (\vec{F}=-k\vec{r}) and the mass rotates with constant speed. At some point in time, a stick of radius a (a<<L)lands near the center of the circle in such a way...
  14. PM22

    Formula to calculate force as a function of angle

    What formula can I use to calculate the force I need to apply to a sliding arm that makes a point contact along the edge of a rotating arm attached to a shaft driving a load in order to push the rotating arm to rotate the shaft? The rotating arm is 1 cm wide. The load at the shaft is 1 Nm...
  15. S

    Equations of Motion of a Mass Attached to Rotating Spring

    1. Homework Statement A particle of mass m is attached to the end of a light spring of equilibrium length a, whose other end is fixed, so that the spring is free to rotate in a horizontal plane. The tension in the spring is k times its extension. Initially the system is at rest and the...
  16. C

    Calculating frictional heat from rotating mass

    How would one calculate the heat generated by a rotating body inserted into a different softer material? Similar to a drill bit, but without the cutting edges so a smooth constant profile across the probe surface.
  17. pac134

    Torque upon a rotating magnetized body

    Hey there! I would really appreciate if someone could help me with the following problem. I didn't find it anywhere (textbooks, web...). Not only currents but also magnetized bodies possesses magnetic moment. I know that if the magnetized body is at rest in a constant external magnetic field...
  18. Ravija

    Variation in pressure in a rotating tube?

    What is the pressure experienced by any point at different locations inside a rotating tube filled with water? The axis of rotation is through the center of the tube.
  19. nysnacc

    Rotating disk find the radial and transverse velocity

    Homework Statement Homework Equations rXF ?? The Attempt at a Solution T= 6 N (r =1) T = 12 N (r=2)
  20. N

    Tension Force between two rotating masses on strings

    Homework Statement Two balls with masses m1=0.3 kg and m2=0.7 kg are connected by massless strings with lengths L1=0.2 m and L2=0.26 m, as shown. The arrangement of strings and masses rotates at constant angular frequency ω=57.6 radians/s around a fixed pivot point. Find the two tensions...
  21. L

    Variational calculus or fluid dynamics for fluid rotating in a cup

    my first post having just joined! Problem statement - what curve describes the surface of a rotating liquid? Stirring my cup of coffee years ago sparked this thought. Question - is the way to solve this problem to use variational calculus, or fluid dynamics? I have always thought the former but...
  22. D

    Bug moving on a turntable rotating with constant omega

    Homework Statement A cockroach crawls with constant speed in a circular path of radius b on a phonograph turntable rotating with constant angular speed omega. The circle path is concentric with the center of the turntable. If the mass of the insect is m and the coefficient of static friction...
  23. nysnacc

    Tangential and Normal of a rotating mass

    Homework Statement Homework Equations at = Rα an = V2/ R = Rω2 Vt Rω Vn =0 The Attempt at a Solution I found at=0 an=5.66 m/s vt=3.364 vn=0 So v = vt = 3.364 m/s[/B] Correct?
  24. moenste

    Two stars rotating about a centre of mass -- Find speed

    Homework Statement The diagram shows a binary star system consisting of two stars each of mass 4 * 1030 kg separated by 2 * 1011 m. The stars rotate about the centre of mass of the system. (a) (i) Copy the diagram and, on your diagram, label with a letter L a point where the gravitational...
  25. K

    Rotating Solenoid: Does It Produce EMF?

    In the presence of a constant magnetic field, does the action of rotating a solenoid (with a fixed amount of coils) produce an emf? Thank you!
  26. K

    Man holding weight, rotating and bringing them closer

    Homework Statement [/B]A man sits on a rotating chair. the moment of inertia of them both is Im. he holds two weights m, each in a spread out hand, and rotates at frequency f1. the distance each mass from the chair's axis is r1. he then pulls his hands closer, each to r2. What's the new f2 and...
  27. hackhard

    Can a Rotating Coherent Laser Beam Create a Persistent Light Dot for Holography?

    if a coherent laser beam rotates about an axis at very high angular frequency can a light dot with radiant glow (of short radius) be obtained due to persistence of vision ?
  28. artriant

    Artificial gravity concept -- Rotating structure in space

    Hello everyone, i m working on a full circle space centrifuge concept. I try to support it with some maths but i don't want to dive into crazy details. I used alrdy lot of countermeasures to dangerous effects.I have problems similar to bridge mechanics. The design is not solid so i need to be...
  29. artriant

    Weights on circular rotating circle

    circular cable i mean ?:)* Hey all second time to use this forum, hope to get same awesome help. Lets say that we have a cable in a shape of a closed perfect circle rotating in perfect conditions no air zero gravity etc around a center. The cable is 100 m circumference, rotating at 1rpm My...
  30. R

    Hi, how to find the magnitude of a rotating vector?

    i get stuck in how to find the magnitude of rotating vector . why say that |dA/dt|=A(dθ/dt) but who we can derive it or interpret this fact
  31. DrClaude

    Phase transition in rotating balls

    A very neat video showing a phase transition in rotating balls in a cup. Serves as a good analogy to other phase transions.
  32. P

    Trajectory of pendulum in frame of rotating disk under it

    Homework Statement Consider the pendulum depicted in the adjacent figure: a mass m is attached to non stretching chord of length `. Directly below the pendulum is a circular disc rotating with constant angular velocity w. We attach to the disk a frame whose x-axis is in the plane of the...
  33. Milo Martian

    Which will reach the bottom faster: solid or hollow sphere?

    1. The problem statement: Consider a solid sphere and a hollow sphere, of equal mass M and equal radius R ,at rest on top of an incline . If there is no slipping which will reach the bottom faster. 2. Homework Equations : acm = Fext/M (cm= centre of mass) angular acceleration= torqueext/ I ( I...
  34. M

    Reverse Rotating Pump: Does it Add Head to Fluid?

    Hi What happens when a centrifugal pump rotate inversely? Does it add Head to fluid?
  35. D

    Calculating Torque for Rotating Beam

    Can anyone help with calculating the starting and stopping torque required to rotate a uniformly laden beam with a total weight of 200kg around a fixed axis. The beam has a length of 2200mm and will be started from stationary, rotated through 70 degrees at which point it will stop and reverse...
  36. X

    Rotational Motion of a pendulum

    Homework Statement A pendulum is made of a bob dangling from a lightweight string of length ℓ. The bob is pulled sideways so that the string makes an angle θi with respect to the vertical, then released. As it swings down, what is the rotational speed of the bob as a function of the changing...
  37. B

    Two Rotating Disks Contacting Along Edge

    Homework Statement Two disks, rotating in the opposite direction of the other, are held together on their rotating ends, acting as toothless gears. The bottom disk is slightly skewed in one direction, and therefore causes a frictional force on the top disk, and thus an equal and opposite force...
  38. K

    Rod rotating and hitting a mass

    Homework Statement A is the pivot at the upper edge of the rod. The rod of length L and mass M stays horizontally. it can pivot round it's edge. suddenly it falls, rotates round A and hits a mass m which gains velocity v. At which angular velocity the rod reaches the mass What is the rod's...
  39. T

    Computer aided Rotating platform

    I'm thinking about building a rotating platform (horizontal rotation, like merry-go-round) which will be controlled by computer instructions. the platform will rotate with accuracy to 1 decimal point degree. a load will be mounted on this rotating platform, could weigh up to 200kg. what's the...
  40. K

    B Calculating Length Along X-Axis for a Rotating Line

    Hi (I hope this is the right place to post this - sorry if it's not) Say I have a line (in the graphic is shown a 10mm but it could be any length) and it rotates around a point at one end. What is the formula to get the length along the x-axis directly under the other end of the line. In the...
  41. S

    Fluid in rotating tube with different initial levels

    Homework Statement Homework Equations Fluid in rotation The Attempt at a Solution This exercise is quite different from the classic one of fluidi in rotation. Before rotation starts the height in one branch is bigger than in the other, so I do not really know how to approach the problem...
  42. E

    Rotating 2D Arrays/Pixels w/o FP or Trig - Can It Be Done?

    Hey everyone, I'm trying to figure out how to rotate a grid of pixels, but I'm have a tough time. For simplicity sake, let's assume the pixels are in an 2 dimensional array, and each index is in a multiple of 8 (0-7, 0-15, etc). Now comes the fun parts: 1.) I can't use floating point...
  43. Narahari Narasapur

    Understanding Coriolis Force in a Rotating Pipe

    Homework Statement Homework Equations https://wikimedia.org/api/rest_v1/media/math/render/svg/1a061d2667e5d9f69dc385e359e7260a3eb1deff https://wikimedia.org/api/rest_v1/media/math/render/svg/ba88069934aa8abb2a2466f84121f385e6e8971f The Attempt at a Solution I have solved equation for r(t) and...
  44. K

    Mass pulling another, rotating, mass

    Homework Statement [/B] The cylinder rolls without friction. what's m's acceleration, M's angular acceleration and the tension. Homework Equations Shteiner's theorem: ##I_c=I_{c.o.m.}+Mr^2## Torque and angular acceleration: ##M=I\alpha## Moment of inertia of a solid cylinder...
  45. K

    Calculating Force Components in a Rotating Link System

    I am conducting some research into finding the force which a rotating link will exert. The link is actuated by a motor which provides 30Nm of torque. I need to find force in x,y,z directions F=[Fx,Fy,Fz]; Is the answer [Fx,Fy,Fz]=[tau/Px,tau/Py,tau/Pz]
  46. C

    Motion of rotating and sliding metal bar for robot combat

    For those who don't know there exists a sport called robot combat. Two robots enter an area and fight until one is unable to move anymore or its owner taps out. I have a novel idea for a weapon for a robot but I am unsure if the maths works out so that it will be practical. Suppose I take a...
  47. Gonzalo Chumillas

    B What Does it Mean When a Black Hole is Spinning?

    The angular momentum is related to the rotation. And when a black hole has angular momentum, it is said that it is a "rotating black hole". But what does it mean? A black hole does not have a conventional surface, like a basketball. How should we interpret that angular momentum? I asked this...
  48. Paul Nicholson

    The easiest way to run wires through a rotating shaft?

    I found this closed thread and I'd like to continue it: https://www.physicsforums.com/threads/design-question-wiring-motors.459672/ I am building a rotating ceiling mount (or rotating a floor plate) and am trying to solve the problem of the continuous rotation servo motor getting in the way of...
  49. grassstrip1

    Angular Momentum of a rotating mass

    1. Homework Statement When the 3.2-kg bob is given a horizontal speed of 1.5 m/s, it begins to rotate around the horizontal circular path A. The force F on the cord is increased, the bob rises and then rotates around the horizontal circular path B. (picture included) Homework Equations L = I ω...
  50. R

    Mechanism for height adjustment of rotating body

    Hi, I am trying to build (or at least conceptually) design a diy autonomous lawnmower. I want to add an automated grass cutting height mechanism. I have never worked with lawnmowers but through basic googling know that most lawnmowers have simple mechanisms in wheels to change cutting height...
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