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. V

    Do our inertial frames rotate with the Milky Way?

    In a 1925 paper, Erwin Schrödinger mentions that "our inertial systems are free of rotation precisely with respect to our stellar system", instead of being "anchored...in much more distant stellar masses". Is this really the case? If so, this suggests that the total gravitational potential...
  2. C

    Why is it only chiral molecules that rotate plane polarized light?

    I just read that the reason molecules rotate plane polarized light is because the light interacts with the electron cloud of the molecule. That makes sense but why aren't achiral molecules optically active? Achiral molecules have electron clouds too so why don't their electron clouds cause...
  3. J

    Weight causing a wheel to rotate

    Homework Statement Homework Equations I_solidcylinder = .5mr^2 I_thinring = mr^2 torque = I*Ω (where Ω = angular acceleration) change in theta = .5(Ω)(time^2) The Attempt at a Solution Attempted to solve for angular acceleration: (2.5)(9.8)(0.1) = (3*0.25^2 + 0.5*4*0.1^2)Ω...
  4. A

    Why a greater torque causes an object to rotate

    Okay, a few days ago I posted a question about torque, and recevied A LOT of useful help on understanding the term. I however must admit, that I still don't quite have the intuition behind why a greater torque causes an object to rotate faster. THEREFORE: Can someone with logical, physical...
  5. S

    Torque to rotate spinning gyroscope

    Homework Statement The Hubble Space Telescope is stabilized to within an angle of about 2 millionths of a degree by means of a series of gyroscopes that spin at 1.92×104 . Although the structure of these gyroscopes is actually quite complex, we can model each of the gyroscopes as a thin-walled...
  6. S

    MATLAB Help Needed: Add Axis, Draw Arm Pieces, Rotate Objects

    LEASE HELP! -Add an axis to current rectangle -Draw both piece of arm -rotate object first axis 20 degree --redraw. -then, rotate 2nd part about 2nd axis to -30degree my current code for rectangle is %RECTANGLE('Position', [x y w h]) w=4.5; %width h=.5; %height x=1.75;y=2.75...
  7. Dadface

    Why Does the Phasor Rotate Anticlockwise?

    When phasors are used,for example to illustrate some of the properties of waves,all of the texts seem to emphasise that the phasor rotates anticlockwise.Why anticlockwise?I have always assumed that the direction is just a convention...or am I missing something?If it is a convention then does...
  8. L

    Do All Black Holes Exhibit Rotation?

    There are two representations of black holes that I see in the popular media. Could you help me find the answer to a (or two) question about this please? 1. Feeding black hole with an accretion disk - I assume that the accretion disk is a product / consequence of rotation (in addition to the...
  9. N

    Maximum force to not rotate a cylinder

    Homework Statement A vertical cylinder is sitting against a wall. It has a weight of 20N and no given radius. A force is applied tangentially in a vertical direction on the side not against the wall. The coefficient of friction is 0.499 for all surfaces. What is the maximum force so that...
  10. S

    What Determines the Direction of Rotation in a Current Loop?

    Homework Statement Consider a long wire running in the vertical direction with a rectangular loop of wire beside it as shown. Now suppose that a constant current, I, flows upward along the long wire, and the same magnitude current, I, flows clockwise in the loop. As viewed from the top...
  11. T

    Does a photon's complex 'amplitude' rotate along its journey?

    Hi, I was watching http://video.google.com/videoplay?docid=-2622437302869951111" the other day and he described photons by an 'amplitude' which actually means a complex number, which rotates over time. This rotation speed gives the photon's colour/energy/frequency. Then later in the lecture...
  12. F

    What motor can rotate up to 50lbs at variable speed?

    I am looking for a type of motor that can rotate gears and a large object and only rotate once every 12 hrs. I am having a hard time located one.
  13. S

    Power Required to rotate a Kiln

    Can anyone help me out in calculating the power required to rotate a Horizontal Kiln resting on Rollers of following data: Kiln Mass 60000 kg Kiln Length 35 m Kiln Diameter 2.8 m Roller Diameter 0.8 m Radial distance between two centers 1.992m Kiln...
  14. R

    Calculating Rotational Force for a 5000kg Suspended Load

    can someone help me?.. i have 5000kg suspended load..how do i calculate the force needed to rotate this load 90 deg. assuming perfect bearing?..thanks
  15. X

    Ball colliding with an arm of an object that can rotate to it's axis

    http://imageshack.us/photo/my-images/195/spinner.png/ ^this is the object/spinner I am referring to. I am trying to code a physics based minigolf game in which a ball should be able to collide properly with the spinner object and the arms of it. However I am lacking in physical knowledge to...
  16. P

    Will a free falling rod rotate or not?

    Will a free falling rod rotate ? When we consider a bicycle is turning on a flat plane, we know that there is friction, which provide centripetal force on the bicycle. And we know that the bicycle is no longer perpendicular to the flat plane so as to reach equilibrium. What I want to ask why we...
  17. M

    Mass needed to rotate wheel and axle (rotational motion)

    I'm sorry for posting another thread but I'm totally lost here.. Homework Statement A wheel and axle having a totel moment of inertia of 0.002kgm is caused to rotate about a horizontal axis by means of an 800g mass attached to a cord wrapped around the axle. The radius of the axle is 2cm...
  18. D

    DC motor - Enough torque to rotate load?

    Hi all, I am new here as i want to ask something about an engineering project i am working on. I need a motor to rotate a 200 grams cylinder which will be hanging from the motor's shaft (vertically). I wanted less than 100 rpm so the motor I chose is a 2.1W 6V DC motor with a 50:1 reductor...
  19. K

    Rotate the area bound by the following lines around the x-axis.

    Homework Statement Rotate the area bound by the following lines around the x-axis. y = x^2+1, y = -x^2+2x+5, x = 0, x = 3 Homework Equations None that are uniform enough to put here considering I'm fairly sure it's not washer... The Attempt at a Solution
  20. Y

    Let a clock A be at rest in an inertial frame and let a clock B rotate

    Let a clock A be at rest in an inertial frame and let a clock B rotate around it with constant velocity and constant distance from A. Let v be the velocity of B relative to the inertial frame. Both clocks count how long it takes for B to rotate once. According to clock A, the time it takes is...
  21. Femme_physics

    Whether an object will slide or whether an object will rotate?

    Let's say I apply a horizontal force on an object sitting on a table. So there's friction. I know how to determine whether it will move or not-- I just see whether the applied force is bigger than the friction force. F > Fs there's movement Fs < F there's no movement That I know. But what...
  22. K

    Low RPM high Torque Motor with enough power to rotate 30 pounds?

    Hi, I'm working on an engineering project and I need to get a 30pound base to rotate at speeds between 6 rotations per hour and possibly 1 rotation per hour. Does anyone know where to get such a motor, or if it is even possible? Can anyone think of a better more efficient way of doing this...
  23. K

    Why does the Moon rotate around the Earth?

    I am doing a project about the earth, the sun, and the moon. My question is why does the moon rotate around the earth?
  24. N

    How much horsepower required for motor to rotate cylinder?

    I done this calculation But something wrong. cylinder weight: 17000 lb weight , Diameter = 36"= 3 ft, length = 5 ft. , 3000 rpm , time=90 sec. Aceee = Change in angular velocity / time Angular velocity = 2xPi (3.14) 3000/60 = 314rad / sec acee = ( 314-0) / 90...
  25. D

    Angle does it rotate & angular acceleration?

    Homework Statement This is a two part problem, but I don't know what equation to use for part II. a) A record has an angular speed of 15.4 rev/min. What is its angular speed? Answer in units of rad/s. 1.61 rad/s b) Through what angle does it rotate in 1.1 s? Answer in units of rad...
  26. T

    Block attached to string, wrapped around hollow cylinder and free to rotate

    Homework Statement A 3.20 kg block is attached to a string that is wrapped around a 1.17 kg, 4.08 cm diameter hollow cylinder that is free to rotate on an axel through the center. The block is released 1.09 m above the ground. What is the speed of the block as it hits the ground...
  27. S

    MATLAB How Do I Find the Volume of a Rotated Solid Using MATLAB?

    I've been trying to solve one of my MATLAB problems for about 2 weeks now and I am completely lost as to how to solve it. It seems like it would be rather easy to do, but I cannot figure it out. I have referenced our Calculus 2 textbook, MATLAB textbook, and Google but I'm still stuck. The...
  28. L

    Work to rotate a dipole in an electric field

    NOTE: BEFORE YOU RESPOND PLEASE KNOW THIS IS AN ASSIGNMENT QUESTION (worth 1/6 % of total subject) AND AS SUCH I DO NOT WANT AN ANSWER TO BE GIVEN TO THIS PROBLEM. I have tried this question many times in different ways and unfortunately I am unable to get any of these multiple choice answers...
  29. K

    How does circularly polarized light rotate a body?

    Everyone affirms that a circularly polarized plane wave has no angular momentum, though it contains density of spin. However, a circularly polarized beam of any big diameter has spin angular momentum, which is localized at the surface of the beam, though the spin is allocated in the interior of...
  30. M

    Why do things rotate? I know what torques are .the question is deeper than that

    Why do things rotate? I know what torques are...the question is deeper than that... This is not any homework or coursework problem. This question has been troubling me since it first popped into my head. Suppose there are two point masses both of mass m, connected to each other by a massless...
  31. U

    Does the ball rotate about its axis?

    Does the ball rotate about its axis?! Hi Newbie here, I have a disagreement with an associate. I say that a ball on a string moving in a horizontal circular path rotates about an axis perpendicular to the said circle. He insists that it doesn't as it would wind up the string if it did...
  32. Z

    Can a body rotate about its centre of gravity ? explain with example

    is it possible for a body to rotate on its centre of gravity
  33. M

    Torque required to rotate a composite structure

    Hi everyone I posted this in the classical physics forum but maybe it is more suitable for this forum. I'm currently trying to select 2 hydraulic motors to rotate a relatively sizeable structure, I'm hoping to rotate it through .5pi radians over a period of 30 mins (0.052 RPM), I'm hoping...
  34. T

    Rotate a plane through its coefficients

    Hello mathematicians, I'm creating a program and I need in this program to rotate some planes around the origin, while I'm given the coefficients a,b,c and d for this plane, they represent a plane of the form: a x + b y + c z = d So these coefficients are given and I want to rotate the...
  35. C

    What Does Our Solar System Rotate Around?

    I know that the Earth rotates around the sun, but what does our solar system rotate around? P.S. I'm a noob when it comes to anything related to astronomy, sorry.
  36. K

    Can any celestal body or anything rotate at speed of 90 degree

    can any celestal body or anything rotate at speed of 90 degree per second with a radius of of more than or equal to 3 X 10 ^ 8 metre ? is it possible?
  37. S

    A block on an inclined plane does not rotate?

    A block of mass m is on a frictionless inclined plane with no initial speed. The net force which equals to the component of the block's weight along the inclined plane, acted through the block's centre of mass, so there is no torque acted on the block, so the block does not rotate and just...
  38. A

    Torque required to rotate something

    Hi guys, was doing some thinking on torque, we all know that we can calculate torque by using T= Force x radius. But let's say if i have a cylinder of mass x kg which has a radius of r, sitting vertically on the floor (flat surface on the floor). How do i determine how much torque is required to...
  39. S

    Looking for proof that a free rigid body will rotate about its CM

    Can anyone recommend a textbook or web paper that proves that, in general, a free rigid body will act in the following way when the body is subjected to a force (or impulse) that is torque producing: a) The center of mass (CM) moves in a straight line. b) The body rotates about an axis through...
  40. S

    Does an artificial satellite rotate in its own axis?

    Hello :) Does an artificial satellite rotate in its own axis? tia
  41. T

    How Do I Calculate the Power Required to Rotate a Cable Drum?

    Hi All, Cable drum, OD-50" weight abt 3 ton.. support by shaft horizontally.Both end of shaft is mounted on bearing. now i need to select electrical motor to rotate the this drum. drum need to rotate constant 30 rpm speed.. please some one help to calculate the power required to rotate.
  42. S

    Why did the bike rotate in the physics experiment in the film 187?

    In the beginning scene of the film One Eight Seven, Samuel Jackson's character has one of his students hold a bicycle while sitting in a chair, and pump the pedals until the wheel got up to around 180 rpm. When he told the student to tilt the bike to the right, the chair started rotating...
  43. R

    Mechanics what force causes a ball rotate up an incline

    When a ball rolls down an incline without slipping friction causes the ball to rotate CCW When a ball with an initial velocity climbs up an incline friction is now in the opposite direction as in the previous case, the problem now is which force causes the ball to rotate CW. It can't be...
  44. R

    Calculate Torque/Power for Rotating Tube & Rectangular Parallelepiped

    I want to calculate the torque of the construction or the needed Power (Watt) to rotate it. The construction is a tube and on top of tube is stuck a rectangular parallelepiped: Tube: inner diameter=d=92mm, outter diameter=D=102mm, lenght=L=3000mm, mass=12.34kg Rectangular...
  45. K

    Why do planets rotate on their axes?

    The title states it all.
  46. M

    Does the earth rotate and undergo revolution with the same speed?

    does the Earth rotate and undergo revolution with the same speed?is the rotation and revolution in same direction
  47. S

    Power to rotate shaft in bending

    How do you calculate amount of power needed to slowly rotate shaft under bending moment? This is not related to transmittal of torque. Given: shaft size span between support bearings bending moment value rpm Assume: slow rotation (ignore centrifugal forces caused by deflection)
  48. K

    Earth & moon rotate round center of mass

    [b]1. Homework Statement Calculate the time the moon rotates once around the earth, and show that you have to add 4 hours to that since the moon & the Earth rotate around their center of mass. hint: use the reduced mass: \overline{m}=\frac{m_{1}m_{2}}{m_{1}+m_{2}} mass of moon...
  49. X

    How fast must the rotor of a generator rotate?

    Homework Statement The maximum indicued emf in a generator is 205rpm is 43.0V. How fast must the rotor of the generator rotate if it's to generate a maximum inducded emf of 55.0V? Homework Equations E= NBAsinwt The Attempt at a Solution 205r/m*2 (Pi)/ 1rev81min/60s = 21.46rad/s magnet...
  50. F

    How gravity make planet to rotate?

    how gravity make planet to rotate? If you asked anybody why things rotate;they will answer you if you mean in astronomy the reson is gravity and if you mean at the level of atom the resone is electracal force but that is not what i want . i want to know how gravity do this and what really it...
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