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. D

    What force is required to rotate a space ship?

    Hi, I was researching the force required to spin a space ship. There is an old thread here but I'm not quite understanding the post. https://www.physicsforums.com/archive/index.php/t-151000.html To move a spaceship forward we have something like F = ma. 1000 kilogram space ship...
  2. A

    Why do the spokes on a wagon seam to rotate backwards at certin speeds?

    This is another thing that I have trouble figuring out. Why do the spokes on a wagon seam to rotate backwards at certin speeds? Help!
  3. V

    Calculate the torque required to rotate a pipe

    Hi, I am stuck on what should be a fairly simple problem. I need to calculate the torque required to rotate a pipe weighing 30 lbs resting on bearings at constant speed. How should my approach be? Do I need to actually measure the torque required using a sensor? Thanks, Mike
  4. S

    Rotate a graph by a given number of radians?

    Is there a way to rotate a graph by a given number of radians? for example, take to standard parabola where the directrix is a horizontal or vertical line, and make it a line of any slope?
  5. I

    Can We Rotate the Earth with a Rocket?

    Hi, My roommate and I were wondering how much energy is needed to rotate the Earth about an equitorial axis. Just as a fun experiment to get Holland into the sun.
  6. C

    NMR Q: Why an RF pulse can rotate Mz so fast

    Learning about Nuclear Magnetic Resonance for a while. I have read than when the main field B0 is applied along the Z axis, it takes a time (T1) in the order of seconds for the M0 field to be created in the body we are studying. Yet we can apply a short (maybe in the order of one wave...
  7. J

    Calculate Velocity of C Rotating About A Axis

    Homework Statement A = (1,1,-2) C = (0,1,-5) (in cartesian coordinates) Let A and C be drawn from a common origin and let C rotate about A with an angular velocity of 2 rad/s. Find the velocity of the head of C. Homework Equations v = w x r The Attempt at a Solution w = 2...
  8. E

    What happens if I rotate a current-carrying wire?

    Let's assume that we have a straight current-carrying wire, along the z axis of the cartesian (or cylindrical) coordinates' system. Biot - Savart law tells as that the magnetic field at a distance r from the wire is dB=\frac{\mu_0}{4\pi}I\frac{d\boldmath{l}\times r}{r^3}, where dl is the wire...
  9. N

    Zero G forces: Translate or Rotate?

    I am working on some 3D physics simulations for computer software (just for fun), and have some general physics questions. Basically, it goes like this: there are 'models', which have 'center of mass' values, 'mass' values, and are made from basic shapes (ellipsoids and boxes). They are run...
  10. R

    How do I stick the panel onto the shaft so it can rotate ?

    Guys, Need some help urgently! I have a thin shaft and a rectangular solar panel. The shaft is connected to a motor shaft and will rotate. How do I stick the panel onto the shaft so it can rotate ? The simpler the solution the better.. Thank you everyone
  11. S

    Would the universe rotate plane polarized light?

    I posted this in cosmology too, but I felt it deserved to be here also. I recently learned something about chemical reactions: A reaction between two achiral molecules will always yield either a symmetrical product or a racemic mixture/s. A reaction involving chiral molecules may yield any...
  12. S

    Would the universe rotate plane polarized light?

    In organic chemistry we recently learned something about chemical reactions: A reaction between two symmetrical (achiral) molecules will always yield either a symmetrical product or equal mixtures of two mirror images (racemic mixtures). A reaction involving asymmetrical (aka chiral) molecules...
  13. T

    Can Dark Matter and Black Holes be Associated in Earth's Rotation?

    ......so,what makes Earth rotate...I believe I'm still in my *discovery*phase(normal for a 15 yrs old..)...sry if this is a newbish question... I though looking on the internet..but so lazy and beside i will prob. not understand with they complicated terms and stuff they'll use to...
  14. S

    Do fins help an object rotate?

    Do fins help an object rotate? example, a nerf football
  15. T

    Rotate point on sphere to exactly 'cut sphere in half'

    Given a point on a unit radius sphere (let's say at coords x=0, y=0.4, z=-0.9165 as shown in the attached diagram), and given a starting angle from 0 to 360 for which the point to travel, what math can I use to exactly 'cut' the sphere in half? For example, the attached diagram below shows...
  16. S

    Force needed to rotate a drum/cylinder

    How do I calculate the HP (torque) needed to rotate a large cylinder mounted on bearings? The cylinder in question is a 8 foot long 12" diameter piece of pipe weighing a couple of hundred pounds, mounted on two end stubs with bearings. Its the business end of a large flail mower and this...
  17. C

    Speed & Distance to rotate 360 degrees

    I have a two part problem to figure out regarding a vehicle loosing control without any outside force except driver input in which it rotates 360 degrees in one direction on a .7f coefficient of friction curved narrow exit ramp. What speed and over what linear distance would be required to...
  18. D

    Rotate in spherical coordinates

    Hello ! In electromagnetics, the electric field of a small dipole in a spherical(r,\theta,\phi) coordinate system is E(\theta)=A\cdot \frac{e^{-jkr}}{r}\sin(\phi)\hat\phi If the dipole is directed along the z-axis. (I used this geometry...
  19. N

    Calculate Shaft Radius for Coupling System, 100rpm Rotate

    Pls help me calculate the shaft radius of a coupling system that's goin to rotate an prespex cylindrical at 100 rpm by a motor... the dia of cylinder is 6 in and its width is 1 in. the material to be rotated is 10 gm s of sand... bulk density if the sand is 3000 kg per m^3...
  20. A

    Why do we rotate along with the earth's rotation?

    I've been having a huge debate about this, some people are saying "air resistance" and that just makes zero sense to me, because the moon has no atmosphere and Neil Armstrong rotated along with the moon with no problem whatsoever. I am thinking it has to have something to do with the...
  21. A

    Could a collision cause Venus to rotate prograde?

    I got in an argument and I was defending one of the theories about Venus' slow prograde rotation. I'm defending the theory which states that atmospheric friction, over a period of billions of years slowed initially fast rotation of Venus and made it go prograde. My opponent says that it...
  22. A

    Power required to rotate the system

    Hai This is first post of mine regarding steady state power requirement. Since i am involving the power requirement project I am posting the question in simple way as follows. Drive & driven both two pulleys are connected by timing belt Drive pulley diameter is 100mm(face width25mm)...
  23. tony873004

    Rotate Area Bounded by y=5, y=x+(4/x) about x=-1: Verify Limits of Int.

    Rotate the area bounded by y = 5,\,y = x + (4/x) about x=-1 Verify the limits of integration x + \left( {4/x} \right) = 5,\,\,x = 1\& 4 solve \begin{array}{l} \int\limits_1^4 {2\pi r\,h\,dx} \\ h = 5 - \left( {x + \left( {4/x} \right)} \right),\,\,r = x + 1 \\ 2\pi...
  24. M

    If an observer accelerates he must rotate in space-time?

    It is my understanding that if an observer accelerates he must rotate in space-time. But then why is that factor generally omitted in the calculations related to accelerations?
  25. J

    Can Gravity Be Used to Rotate Pulleys?

    Cross section of pulley1, pulley2 , pulley3 and pulley4 are as shown in figure. Centres of Pulley 1 and pulley 2 are placed on same horizontal line. Centres of pulley 1 and pulley 2 are fixed. Pulley 1 and pulley 2 can rotate about their centre. Centres of pulley3 and pulley4 are also placed on...
  26. N

    Why Does a Planet Rotate and What Factors Influence Its Angle of Rotation?

    Hi. I can't seem to understand why a planet has to rotate about its own axis as it revolves about the sun. Why can't it just revolve around the sun without any rotation? What is the cause of rotation of a planet? Also, on what factors does the angle between the axis of rotation and...
  27. T

    Why is the solar system, & galaxies seemingly rotate on a 2-D plane?

    Is this true and why?
  28. V

    The moon doesn`t rotate around it`s axis.

    Does the moon rotate around it`s axis? for images see please: http://omega.webzdarma.cz/applety/moon/moon.html The moon doesn`t rotate around it`s axis, I think. In many books the moon does rotate around it`s axis. I have never undrestood why. Let mi introduce my point of wiew. We feel...
  29. K

    How does the Orbital Electron Rotate Permanently without Energy Supply?

    Is there anyone who knows the answers of these two long-standing questions? 1. How can the orbital electron rotate permanently without energy supply? 2. How can the orbital electron keeps its position without merging into its nucleus when an external pressure applied on it if its kinetic...
  30. B

    Why does a gas cloud spontanously rotate?

    I have read numerous books that describe the formation of a solar system from a cloud of gas. They state that as the gas contracts it rotates and as it rotates it flattens out into a disk. I do not understand why the gas molecules start to rotate, how the gas molecules decide which way they are...
  31. wolram

    What Causes the Expansion of the Universe?

    http://arxiv.org/abs/astro-ph/0509230 Authors: George Chapline (Lawrence Livermore National Laboratory), Pawel O. Mazur (University of South Carolina) Comments: 5 pages, LaTeX file, 1 figure Understanding gravitational collapse requires understanding how $\sim 10^{58}$ nucleons can be...
  32. wolram

    The Rotation of the Universe: A New Perspective on Cosmic Expansion

    http://arxiv.org/PS_cache/astro-ph/pdf/9703/9703082.pdf http://arxiv.org/abs/gr-qc/9604049 Authors: V.A. Korotky, Yu.N. Obukhov Comments: 22 pages, Revtex Journal-ref: Published in ``Gravity, Particles and Space-Time'', eds. P. Pronin and G. Sardanashvily (World Scientific: Singapore...
  33. I

    How does a ball rotate in a waterfall?

    I needed to check if I was correct in my thoughts about how a ball rotates under a waterfall. Let me describe the situation: there is a mini-waterfall in my pool that has water that flows like a sheet (smooth water without any gaps, if that makes sense). Whenever a ball is placed near the...
  34. D

    Calculating Energy to Rotate Magnetic Dipole in Solenoid

    i received this problem from my lecturer A solenoid is wound with 2200 turns per meter, and carries a current 2.5A. Take the axis of the solenoid to the solenoid to be parallel to the z-axis. A magnetic dipole moment given (m)=(20A.m^2)i+ (30A.m^2)k is located inside the solenoid. i)how...
  35. E

    Rotate Image Using Cosine Function in Delphi: A How-To Guide with Explanation

    I am using the Delphi language, and I want to learn how to use the Cosine function to rotate an image. Can somebody please explain how and why the math works. I know what cosine is, I just don't know how to use it in any real situations, can somebody please tell me how to do this? Delphi =...
  36. B

    Can a wave rotate about its axis?

    Can a wave rotate about its axis?? Can a transverse wave "rotate" about its longitudial axis (kind of like an airplane's "roll" maneuver)? If it could, i don't think we could detect it; if it did, i don't think anything will really get affected. But could it?? Not that it would...i mean...
  37. N

    AZING SPACE: Understanding Orbital Motion

    Why does the Earth rotate?
  38. F

    Why does the earth rotate around its

    Why does the Earth (or any planet for that matter) rotate around its axis?
  39. A

    Can you throw a knife that doesnt even rotate or spin

    Specially in the movies... i see people throw knives at enemy's neck or the head instantly killing them... some of the knife i saw.. fly straight without any rotations... how can you throw a knife that doesn't even rotate or spin... and travel straight with high velocity ? ( and the mass is...
  40. R

    Can we rotate 3D objects in 4D space?

    Suppose you have a piece of paper in the shape of a left shoe, on a flat surface. Suppose also that it can only stay in contact with the surface. No matter how you move it or rotate it in the 2D surface, it cannot become a right shoe. However, if you move it out of the 2D space, flip it and...
  41. N

    How does the Earth's rotation affect our planet?

    why does the Earth rotate?
  42. V

    MATLAB How Do I rotate f(x) around the x-axis in MATlab or Mathematica?

    Please help, I want a visualization of the function y = sech(x) revolved around the x-axis from x = -2 to 2, creating a "solid of revolution". :confused:
  43. J

    Why Do Hurricanes Always Rotate Counter Clockwise?

    Down here in Florida we are about to see our THIRD HURRICANE OF THE SEASON. Unbelievable is the chaos that is going on. :eek: Anyway, just wondering what causes a hurricane to rotate counter clockwise? Jason SW Florida Hurricane Charley, Hurricane Frances, & approaching Hurricane...
  44. M

    Do Black Holes Rotate and Explode?

    Ok so Stars that go suprnova, and explode to become Black holes, Do the black holes continue to rotate around the galaxy? or do they just die in space, and wait for other stars to come by?
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