What is Rotate: Definition and 244 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. M

    Torque to rotate pulley with equal mass on each side.

    Lets say there is a pulley attached to the ceiling. Hanging on the pulley is a rope and on each end is a 1000 lb. weight. I believe that theoretically it wouldn't take any torque at all to rotate the pulley if it were frictionless (maybe inertia would play a role, but let's ignore that)...
  2. G

    A How can I find the collision time of 2 ellipsoids that rotate

    I have 2 ellipsoids: Ax^2/a^2+Ay^2/b^2+Az^2/c^2=1; (*a,b,c>0 constants*) Bx^2/a^2+By^2/b^2+Bz^2/c^2=1; Ellipsoid A rotates around axis [wax;way;waz] (unit vector) with an infinite speed; Ellipsoid B rotates around axis [wbx;wby;wbz] (unit vector) with an infinite speed; [Dx;Dy;Dz] is the vector...
  3. P

    Force needed to rotate a drum

    I need to make sure that my drum which is connected to a shaft and with load of 30kg is able to rotate at 6500rpm. mass of drum : 15kg, diameter 0.6m, length, 0.6m mass of shaft : 11kg, length = 1m, diameter, 0.043m mass of load : 15kg desired speed : 6500rpm in 30minutes. How can I determine...
  4. S

    Rotate only H-Pol Component of Light beam by 90 degrees

    Is there a single optical component that will do the following? Do nothing to the horizontally polarized input, but rotate the vertically polarized input by 90 degrees, so that both beams finally emerge with the same polarization? I am looking for a single element that will replace the...
  5. Avimanyu Ray

    I What causes retrograde rotation in planets and moons?

    When I googled it, I wasn't satisfied with the answers from various sites...some sites like universetoday.com gave me a glimpse but it was totally theoretical and based on assumption. Also I would like to know why some planets have retrograde rotation; what might have caused them to and why do...
  6. JohnS-I

    Torque needed to rotate a cylinder

    Hello, I'm designing a machine as a final assignment for my internship. It's a machine that wraps SS tubing around a cylinder, making coils. While trying to figure out how much torque I'd need to rotate the cylinder I found that I'm really in the dark on the subject (the teacher I had didn't...
  7. hansyhop

    Motorized rotating platform (180 degrees, periodically)

    Hi, I'm trying to build a motorized rotating platform, and was wondering what drive system to choose. The platform is 1.2 meters in diameter with two cylindrical objects (max 25 kg each) attached on top - total weight to rotate approx 80 kg. I want the platform to be programmed to...
  8. A

    Does a rod rotate under gravity?

    Hello. Say you have a uniform rod in free-fall. Would it rotate? Suppose you compute the rotation around the CM. I computed that the lever arm is the same on either side, regardless of the angle at which the rod falls, so there can't be any rotation. So if I just dropped a 30º to the horizontal...
  9. N

    How to compute the location of the antenna when I rotate it?

    Hi group, I have a question regarding to detect the location of the antenna. I read this link: https://en.wikipedia.org/wiki/Plane_wave In the "Complex exponential form" part, the equation: U(r,t) = U0 * exp(j*(k.r - w*t) as the function of location and time U0 = A0 * exp(j*phi) : A0 and...
  10. T

    I Gyroscopic Precession: Understanding the Physics

    I was watching this and I get it that when you rotate the wheel, the torque due to its weight will cause it to revolve parallel to the ground instead of perpendicular to the ground. I know that the faster you spin the wheel, the less likely the lever from the wheel to the pivot will be slanted...
  11. S

    How Much Torque is Required to Rotate a 1500lb Steel Drum?

    We have a 1500lb steel drum that has a 8 foot diameter that we need to rotate to wrap up air filter material. The drum is supported by bearings on both sides and needs to turn at 0.02rpm. I calculated the torque, using T=Moment of Inertia * Angular Acceleration. For the moment of inertia I...
  12. P

    Can an astronaut rotate herself?

    Homework Statement An astronaut has been left outside the space station, her back towards the station. The astronaut is not rotating (angular momentum ~ L = 0) and cannot reach anything. Is it possible for the astronaut to rotate herself into facing the space station? Homework Equations...
  13. E

    How much force (N) would it take to rotate this object?

    As depicted in the picture. Sorry, I have minimal experience with physics at all lol, but my paint game is strong right? It is a 1 kg object with the center of mass perfectly in the center, rotated 90 degrees in 0.1 seconds. What about in 1 second? http://imgur.com/OIOdZ6f...
  14. H

    How does a rod rotate due to gravity?

    Homework Statement Imagine a uniform, symmetric rod, free to rotate around an axis going into the computer screen through the center of the rod. Now say that we start off the rod so that it is not horizontal or vertical, but somewhere in between. My intuition tells me that the rod will start...
  15. I

    Torque needed to rotate shaft in pipe?

    I have a shaft within a pipe, all horizontal. Shaft diameter is 2.875" and pipe inner diameter is 5". Shaft and pipe length is 650 ft. Shaft weight is 2500 lb. I need to determine the torque needed to begin rotating the shaft. The coefficient of static friction between the shaft and the pipe is...
  16. 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...
  17. peter010

    Possible webpage title: Will Applied Force Cause Rotation on Axis M-N?

    Homework Statement A force F is applied over axis M-N in the such shown position. Both of points A and B are not fixed, and can slides inside the black fixed circle. will the applied force (in the shown position) cause the axis M-N to rotate ? if it is not rotating, then what modification...
  18. slick_willy

    Why does atmosphere rotate w/ constant angular velocity?

    Hey guys. I've seen this question asked on a few different forums, and I understand the basic gist of the answer but I am not yet satisfied with what I have read. People seem to have varying degrees of understanding of this, and I am the type of person that wants to understand things 100% and...
  19. L

    B Does the moon rotate on its axis?

    I googled this question and found sources which claimed the moon slowly, over about 27 days, rotates on its axis. Yet wouldn't rotating at a speed so that about 40% of the moon never faces the Earth suggest that it is rotating around an axis somewhere inside of the Earth, rather than inside of...
  20. barryj

    Why Does a Football Rotate in Flight?

    When a football is first thrown it is usually tip up but during the trajectory, the ball tends to rotate where the tip is pointing down. Why does this occur?
  21. 5P@N

    How do you calculate joules necessary to rotate an object?

    NOTE: THIS IS NOT A HOMEWORK QUESTION! I merely wish to know how to calculate the force necessary to rotate an object, say of 10 kg, from a certain downward diagonal direction of 45 degrees into an upright position considering only gravity. I'll need to use some formula involving torque...
  22. W

    Most efficient way to rotate a cylinder using a motor?

    This is my first post on these forums, and I was hoping someone could answer a question I have. For my high school engineering course, we spend most of the year developing a solution to a problem of our choice. We are currently developing a composting tumbler that will turn automatically several...
  23. V

    Torque required to rotate 5 flywheels connected with 1 belt

    Hi, I have 5 machines with flywheels, which are connected with one single belt, so that all five flywheels rotate together. Torque required for each flywheel to rotate is 300 Nm and rpm is 500. what would be the total torque required to rotate five flywheels connected with one belt?
  24. stackprogramer

    An electron in atom that rotate proton, has it radiation?

    Hi dears,i have a question about atom,in classic physics ,(Bohr theory) when a electron swing away a proton it have not radiates magnetic waves because if electron radiates magnetic wave it will drop on proton ,and atom will be Unstable! my question is ,in quantum mechanics that uses orbitals...
  25. A

    Work needed to rotate armature of a generator

    Pls give me an eq relating work needed to rotate armature of generated
  26. I

    What happens when you rotate a rigid body

    Hi, I have a question about rigid body rotation. If I have a rod out in space in free float and I attach a battery powered fan to center of mass and then the fan is turned on to spin in a clockwise direction, then the rod should spin in a counterclockwise direction. This much I...
  27. A

    Power required to rotate a disc in a fluid

    Homework Statement This is an optional question given to Fluid mechanic students to work on for leisure. P = power ρ = fluid density, rho ω= angular velocity omega μ= dynamic viscosity, mu D= diameter Homework Equations Show the that the power required to rotate the disc is given by...
  28. T

    How can I use matrix algebra to rotate a polygon and calculate new coordinates?

    Let's say I have a 5 vertex polygon drawn on a x/y graph. Each of those vertices have an x/y coordinate. Now let's say I want to rotate the polygon 25 degrees clockwise and calculate the new coordinates of each vertex. How can I do that so that by knowing the original coordinate I can do a...
  29. P

    Magnetic Rotation: Will South Pole Move to North?

    If I have a magnetic setup in frictionless, etc. area as follows: N / / / ---------------------S Will the "south" pole rotate up to the "north" pole, causing the system as a whole to rotate?
  30. EternusVia

    Why do enantiomers rotate polarized light?

    We are currently learning about enantiomers in organic chemistry class. So far, we've covered what makes an enantiomer, the concept of chirality, optical isomer naming systems, and the physical and chemical properties of enantiomers. One of the physical properties listed is that enantiomers...
  31. S

    Why Does Everything in the Universe Rotate?

    Do we know why everything in the universe rotates? The dust clouds, stars, planets all rotate. Even galaxies rotate. Why is that? Gravity causes the dust particles to accrete into rocks and then asteroids, planets, and stars. But why the rotation. Similarly, why is our galaxy such a relatively...
  32. C

    Car C1 Speed Needed to Rotate C2 180 Degrees

    A car (C1) coming in the opposite direction hits the other car (C2) at right angle. The car which gets hit, C2 rotates in 180 degrees. What was the speed of the car C1? Assumptions: Both cars have same tyres. W of C1 =3200lb (2012 Honda Accord)...
  33. mooncrater

    A disc in space will rotate or not?

    Homework Statement Consider this question: "A uniform thin flat isolated disc is floating in space. It has radius R and mass m. A force F is applied to it at a distance ##d=\frac {R}{2}## from the centre of the disc. So, Will the disc rotate with accelerating in the direction of force or it...
  34. S

    Why will a pipe pulled around a curve rotate no torque

    Hello everyone, I am not a physicist nor do I know that much about physics. I do however have a physics question and this seemed like a great place to get an answer. I will present my situation the best I can. I work in the Horizontal Directional Drilling industry. This industry installs...
  35. Spinnor

    Rotate a three-sphere so every point moves in R^4?

    If we rotate a two-sphere in R^3 so it stays centered about the origin then two points don't move. If we rotate a three-sphere in R^4 while it stays centered about the origin can it be done so that all points move? Does this have anything to do with the fact the S^3 is parallelizable while S^2...
  36. PhiowPhi

    Why wouldn't the disc/paper rotate?

    I was playing around a piece of paper by placing my pencil in the center and applying torque on the pencil(pencil Y-axis paper x-axis vice versa), and that torque transmits to the paper as well and it starts to rotate. Then I moved the pencil to the far edge of the paper and applied torque there...
  37. R

    How can we calculate the required torque to rotate 1200 kg?

    I want to calculate torque to rotate 1200 kg of mass which is attached in 1.5" dia shaft. Shaft is supported by 2 bearings at its end. Neglect bearing frication. Please help.
  38. wirefree

    Two cylinders: free to fall and rotate

    Problem: Find the acceleration of the blue cylindrical disk. Both, red and blue, cylinders have same mass and radius, and string is massless. Attempt: Identified three equations: one for linear acceleration of blue cylinder, and two of angular accelerations (one each for blue and red...
  39. B

    Torque Required to Rotate a Drum

    I need to figure out the torque required to rotate a drum. The drum is being rotated on its perpendicular axis. I am designing a drum dumper so the drum starts upright and is rotated 135 degrees to dump its contents into a hopper in the floor. I want it to take about 5 seconds to do the rotation...
  40. P

    Max Drum Rotate Speed of a Concrete Mixer Drum

    Homework Statement In a concrete mixer, cement, gravel, and water are mixed by tumbling action in a slowly rotating drum. If the drum spins too fast the ingredients stick to the drum wall instead of mixing. Assume that the drum of a mixer has radius ##R = 0.5 m## and that it is mounted with...
  41. D

    Time to rotate system 20 degrees

    Homework Statement In the system of Problem 2-6, we need move the load by 20 degrees and bring the system to rest. Assuming a triangular speed profile of the load with equal acceleration and deceleration rates (starting and ending at zero speed). Assume a coupling efficiency of 100%. The...
  42. Y

    Magnet/Electricity to rotate object 90 degrees?

    Hello, I want to create a motion using electricity, using the cheapest means possible (DIY). Basically I'm trying to rotate an object 90degrees when the current is on, and back to its original position when the current is off. The questions are: 1) Is this possible? 2) Can this be done using...
  43. S

    How much power motor I need to rotate big ferris wheel

    Hi Guys, I am pleased to join this forum to learn something from experienced guys and thanks in advance for helping me to understand physics. I am trying to design a Ferris wheel with maximum SPEED and maximum PASSENGER capacity. I want to know formula to calculate MOTOR POWER IN KW to rotate...
  44. X

    Calculating torque required to rotate objects

    I don't have any background in any physics past high school, so I was wondering if someone could help me figure something out. I'm trying to build a robot that involves shooting off a foam bullet from a Nerf gun at different angles. I want to have a motor attached to the center of the gun...
  45. T

    How to rotate a triangle in an equation

    Hi, i have a set of definition for a triangle shape: -3/4<x<3/4 -x/sqrt(3) + sqrt(3)/4 < y < x/sqrt(3) +sqrt(3)/4 The centroid of this triangle is at 0,0 i want to rotate this triangle by a certain degree from the centroid but i am not sure how, because if i just multiply it by cos or sin...
  46. IamDev

    Setup Design to rotate the work piece in DIE sinking EDM process?

    I need to design a basic setup to rotate the workpiece in Die Sinking EDM Process. I made some design but they were complicated and were not easy to fabricate so I need someone who can help me.
  47. R

    Use viscosity/shear stress relations to find torque needed to rotate disk

    The problem asks for an approximation for the torque needed to rotate a disk that is separated from a stationary boundary by a viscous fluid, given that \tau = \mu \frac{U}{H}. I did it first using like this: T = F R F = \tau A = \mu \frac{U}{H} \pi R^2 where U = \Omega R And thus T = \mu...
  48. P

    Low Speed High Torque Motor for 5kg Rotating Project

    i want to ask something about an engineering project i am working on. I need a motor to rotate a 5 kg with less than 5 rpm(low speed high torque motor).please help..
  49. M

    What is the angular velocity that the rod will rotate

    Hello! I'm pretty much translating this question word by word, so if you have problem understanding something off of it, please, let me know and I'll try explaining it better. Homework Statement Two masses of similar mass M are connected by a rod of length 2a. the rod is rotating on a...
  50. A

    Time to Rotate Metal Sphere 1 Time

    Homework Statement A girl pushes on a large stone sphere. The sphere has a mass of 8200 kg and a radius of 90 cm and floats with nearly zero friction on a thin layer of pressurized water. Suppose that she pushes on the sphere tangent to its surface with a steady force of F = 45N and that the...
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