Rotation 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. M

    MCNP TR Transform Card Question

    I'm trying to rotate an RPP 45 degrees around the y axis (BUT NOT THE ORIGIN Y AXIS, rather the y axis at x=a, z=b). Is there a way to do this in MCNP? I've tried every single possible combination of angles and inputs to no avail. Again, I have an RPP that is not centered at the origin and I...
  2. bigdoghustler

    Need advice on making my lamp! Turn dial into string pulled mechanism?

    Excuse my lack of knowledge and please correct me on anything! I'm making a lamp right now and the vision is to have a dimmable lamp in which there are two strings controlling to the potentiometer. To increase the brightness, one string is pulled down and the other will go up. I have a lamp with...
  3. Pencilvester

    I A beginner’s thoughts on rotation number -- Resource suggestion request

    I have been thinking about rotation number of regular smooth curves in different surfaces. Here is how I’ve been defining these things: a regular smooth curve is a map from ##S^1 \rightarrow \mathbb{R}^2## whose derivative is non-vanishing. If we have a regular smooth curve ##\gamma## as well...
  4. S

    PhysicsForums is rotating my photographs sideways

    I would like to create a thread to ask a question about plumbing. I have used my cell phone to take photographs of a book about plumbing, and I would like to post these photographs on my thread about plumbing. But when I was in the process of creating a thread, and I posted the photographs on...
  5. Old Man Scho

    B Tangential Velocity (maybe)

  6. Irvin Atkins

    B Move in Space without mass exchange

    I did a thought experiment and I can't figure out what the mistake is. There is a system of 2 electric motors weighing 1 kg each with batteries in the Earth's orbit. The motors are rigidly connected by a 1-meter-long bar. If one motor starts rotating in one direction on a signal, the entire...
  7. B

    I Confusion about adding angular velocities

    I'm trying to learn about adding angular velocities, and I'm confused about something. In this diagram... https://i.sstatic.net/S6C03.png there is a large orange disc rotating with angular velocity A (relative to the ground), and attached to the large orange disc is a small green disc, which is...
  8. S

    A Exact meaning of the mass M in the Kerr metric event horizon formula?

    Posting this as I have so far not been able to find a straightforward answer to the following question. The formula for the outer event horizon of a kerr black hole is given by the following equation: $$r_+ = \frac{GM}{c^2}\left(1+\sqrt{1-\frac{J^2c^2}{M^4G^2}}\right)$$ Where ##J## is the...
  9. nafisanazlee

    Can Energy Conservation Solve the Angular Velocity Problem?

    Let the mass of the ball m₁ and the disk m₂ m₁vrsinθ = I₁ω + Ι₂ω I₁ = m₁r² and I₂ = ½m₂r², r=3m, rsinθ = 2m. Is this a correct approach? if not, what is? Can this be solved using energy conservation?
  10. R

    Looking for observed rotation periods of various Foucault pendulums at different latitudes

    Hello, I am currently doing research on the Foucault pendulum, specifically on its rotation period. I was wondering where I could find data concerning the observed rotation periods of various Foucault pendulums at different latitudes around the world (not calculated using the Formula T=24/sinλ)...
  11. M

    Direction of Plane Engine Rotation

    Hi All, Do the left side and right side engines of a plane rotate in the same or opposite directions? Is the angular momentum (gyroscopic effect) of the engine shaft, blades, etc., sufficient to affect the flight path of a plane with large engines? In military fighters, such an effect could be...
  12. Kostik

    A Making sense of Dirac's rotation operator in "General Theory of Relativity"

    In Dirac's "General Theory of Relativity", Chap. 34 on the polarization of gravitational waves, he introduces a rotation operator ##R##, which appears to be a simple ##\pi/2## rotation, since $$R \begin{pmatrix} A_0 \\ A_1 \\ A_2 \\ A_3 \end{pmatrix} = \begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 0 &...
  13. sbrothy

    Correct phrase involving optical rotation of venom

    What it said in TL;DR: I want to describe a situation where a laboratory technician synthesizes the wrong isomer(?) of a naturally occurring venom, ending up with the left hand molecule when aiming for the right hand one. However improbable that may sound to a bunch of pros like you. It's for...
  14. mdcreator

    B What is physical significance of the direction of angular velocity?

    This question has been bugging me for quite a while, That what do we mean by direction of angular velocity or torque. As we know that the direction of angular velocity or torque even is determined by right hand thumb rule, and it come out to be perpendicular to the rotational plane. So my...
  15. R

    I Why does a free rigid body rotate only about its COM when F(ext) is applied?

    Why a free rigid body with mass m, when applied with an external force F, translates with center of mass and all particles of body having same linear acceleration = F/m, but it always rotates only about its center of mass, but not about some any other point on the body? And, thus if the line of...
  16. F

    I Rotating plate thrown parallel to ground

    [Image below] I'm trying to figure out how much information I can get from and accelerometer and gyroscope attached to a spinning plate that is thrown through the air. It has both linear and angular acceleration/velocity. The plate is hand thrown fairly parallel to the ground. Z axis points in...
  17. Heisenberg7

    B Rolling Without Slipping on an Inclined Plane

    I have asked this question last year (on discord; IPhO server) and I believe I wasn't satisfied by the answer at that time, but I let it go. Today, as I was going through some physics videos on YouTube a video about it popped up. So, I would like to address this issue now. Let's imagine an...
  18. M

    I Galaxies as systems extended from the solar system

    Is it a big assumption that Galaxies should follow Kepler's third law with rotation speeds decreasing with distance from the centre. Is the small tet of the behaviour of the Solar System not too small an example to make such a substantial assumption? Thanks Martyn
  19. Sam Jelly

    A rod sliding/falling down on a frictionless horizontal plane

    This is the answer to this question why? My attempt :
  20. doke

    Rpm and power for this electric motor, gearbox and pulley system

    i got confused because if the connections btw the parts
  21. Anisur Rahman

    I What Happens to Rotational Velocity When AC Part is Dropped?

    In figure AO = OB = 4m. C is the midpoint of AO. The rod rotates with a velocity of 5 rad/s about the axis PQ. What will be the rotational velocity of the remaining rod if AC part is suddenly dropped from the rod? Assume that the mass of this uniform rod is M.
  22. N

    Wavefunction of a space and spin rotated state

    Since ##U## is a space and spin rotation, it would be $$U(R) = e^{-i\textbf{L}\cdot \hat{\textbf{n}}\phi/\hbar}\cdot e^{-i\textbf{S}\cdot \hat{\textbf{n}}\phi/\hbar}$$ And, then $$\psi'(\textbf{r}, m) = \langle\textbf{r}, m|e^{-i\phi(\textbf{L} + \textbf{S}) \cdot...
  23. N

    Electron moving in an electromagnetic field and rotation operator

    Hello, The idea I had was to time evolve the state ##U(\hat{\textbf{b}}, \omega t)| \phi(t) \rangle##, but I'm confused on how to operate with ##H## on such state. I Iwould be glad if anyone could point some way. Thanks!
  24. F

    Deriving a formula for KE (rolling + projection)

    I'm not sure where the equation E_k=(gmR^2)/4h comes from & I also don't really know where to start either :(
  25. M

    Cut lemon moved by itself

    Hi , In one of my friends place , she cut the lemon in half and left it . She saw the lemon rotated to other direction by itself . She saw it twice on different days ,why does this movement occur ?
  26. T

    I Seifert -Solutions of Einstein's equations give flat galactic rotation curves

    The Importance of Being Symmetric: Flat Rotation Curves from Exact Axisymmetric Static Vacuum Spacetimes ... Analyzing the low-velocity limitcorresponding to the Newtonian approximation of the Schwarzschild metric, we find an effective logarithmic potential. Thisyields flat rotation curves for...
  27. C

    Engineering Help Calculating Length And Position Of Connections On Rotating Object

    Hi, i need to find a formula or calculation that would allow me to connect three lines when rotating. The three lines must fall so that they mirror themselves on the opposite side. I need to be able to calculate this for now just the example above but be able to apply to a range of lengths and...
  28. R

    A Rotation speed for a particular system under gravity

    You have a rope hanging over a fixed support with a heavy weight at one end and a lighter weight at the other end. You set the end of the rope with the lighter weight spinning in a circle and let the heavy weight end fall under gravity. As the heavy end falls the length of the rope that is...
  29. M

    Friction - same direction as motion?

    Doesn't friction always oppose the motion? From the clockwise rotation here, shouldn't the cylinder be moving to the right? so why are the acceleration and friction in the same direction to the right, and in the same direction as the motion? (attached image for reference)
  30. Bling Fizikst

    How Does Coriolis Force Influence Particle Motion in Rotating Systems?

    Source : JEE Advanced , Physics Sir JEE YT I tried to attempt it using Lagrangian , so according to the coordinate axes given in the diagram , the position of the particle is let's say ##(0,d,-z)## Let ##r## be the distance between the particle and the axis of rotation such that it subtends...
  31. P

    2 Masses and a Wheel (with mass)

    The equation that connects final velocity with distance traveled is ##v_f^2 = v_i^2 + 2a \Delta y## Since the system starts from rest ##v_i = 0## and the above equation becomes. ##v_f^2 = 2a \Delta y## Since there is rotation in this system we need to connect ##a## to the rotation of the...
  32. M1N

    Calculate the frequency of rotation when a coin flies off a turntable

  33. U

    Does a Rotating Wind Tunnel Impact Airflow on a Turning Vehicle?

    Why this wind tunnel rotate?
  34. R

    Question about torsional shear stress

    If a circular rod is allowed to rotate freely and a moment (M) is applied to one end of the rod. A moment acting in the opposite direction, with magnitude (M/3), is applied to the other end of the rod. What is the maximum moment in the rod that would be used to calculate the maximum torsional...
  35. K

    A How Are Rotations on the Bloch Sphere Implemented in Practice?

    Hello! I am curious about how different rotations on the Bloch sphere are done in practice. For example, assuming we start in the lower energy state of the z-axis (call it |0>), a resonant rotation on the Bloch sphere by ##\pi/2## around the x-axis will take you to ##\frac{|0>-i|1>}{\sqrt{2}}##...
  36. S

    I What Causes the Einstein - de Haas Effect in Iron Rods?

    This effect is (apparently) always explained in terms of a "book-keeping" need to conserve angular momentum. I totally get that (as the kids say these days), but it doesn't provide a chain of cause and effect that leads to the observed rotation of the iron rod. Is there a classical thought...
  37. pedrovisk

    I Newton's second law for rotations

    EDIT: I forgot about Second Newton's law for rotations and this led to a mistake. Anyway, thanks for the people who answered it and remembered me about law of inertia. I was thinking about how to "make" things to move without rotate the object, then i tried to calculate the minimum force to...
  38. K

    I Anomalous contribution to galactic rotation curves due to stochastic s

    Anomalous contribution to galactic rotation curves due to stochastic spacetime Jonathan Oppenheim, Andrea Russo Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Theory (hep-th) another way to explain MOND in...
  39. P

    I Coriolis effect and the acceleration experienced in a rotating frame

    Is the reason behind coriolis acceleration is that as you move far from the centre of a rotating frame the tangential velocity increases?
  40. S

    Spinning a Bucket to measure gravity with the parabolic surface of the water

    I did (A) by balancing force on point p (in the figure). I found slope , tanθ = (w^2)x/g. I dont know what to do next. Pls help
  41. T

    I Velocity transformation between frames rotating relative to one another

    Good evening, I was wondering about how velocities transform when two successive rotations are applied. In other words, how is the transformation law between two frames which are rotating relative to another. Lets say some particle is moving with a velocity v in an inertial frame S. If we go...
  42. cianfa72

    I Is the Belt Trick Possible with Continuous Deformation in 3D Rotation Space?

    Hi, in the following video at 15:15 the twist of ##4\pi## along the ##x## red axis is "untwisted" through a continuous deformation of the path on the sphere 3D rotations space. My concern is the following: keeping fixed the orientation in space of the start and the end of the belt, it seems...
  43. Miles Behind

    "2001 A Space Odyssey" space station: Rotating or contra-rotating?

    I assume that a space station like portrayed in 2001 A Space Odyssey could either be fixed in rotation, or contra-rotating. Is there an advantage of one over the other?
  44. T

    I Is angular momentum perpendicular to fixed axis of rotation constant?

    So my book states torques perpendicular to the fixed axis of rotation tend to tilt the axis , however we assume sufficient restraints exist so these torques are simply ignored. It follows that angular momentum perpendicular to axis remians constant. (See image ) My question is that if a rod is...
  45. D

    B Why does a coin take 2 full rotations around another coin?

    This one baffles me, I still can’t get my head around it (no pun intended). Take 2 US quarters. Put them in contact side by side. Without slippage, roll one quarter around the circumference of the other until it returns to the starting point. It requires rotating the moving quarter 2 full times...
  46. E

    How Do Two Rotating Rods Interact?

  47. apcosta

    What should be the geometries of two contacting solids that may have a relative rotation and translation along the same axis?

    TL;DR Summary: What should be the geometries of two contacting solids that may have a relative rotation and translation along the same axis? a) Consider two rigid bodies that have a relative motion characterized by a rotation and a translation with respect to the same axis (like a bolt and a...
  48. Codezero

    I Modeling Asteroid Rotation Using Quaternions: Seeking Guidance on Init

    Hello everyone, I am an International Baccalaureate (IB) student working on my extended essay, which is a mandated 4,000-word research paper. My chosen topic is Quaternions, a mathematical concept I find highly intriguing. The primary aim of my paper is to model the rotation of an asteroid...
  49. U

    I Do objects always rotate around center of mass?

    For example if airplane or boat move rudder, do they always rotate around center of mass? Or exist specific conditions when object rotate around center of mass?
  50. Sciencemaster

    B How to find the infinitesimal coordinate transform along a hyperbola?

    I've been told that the infinitesimal change in coordinates x and y as you rotate along a hyperbola that fits the equation b(dy)^2-a(dx)^2=r takes the form δx=bwy and δy=awx, where w is a function of the angle of rotation (I'm pretty sure it's something like sinh(theta) but it wasn't clarified...
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