What is Rotating: Definition and 1000 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. wirefree

    Is My Approach to Calculating the Length of a Rotating Compound Pulley Correct?

    I am appreciative of the opportunity afforded by this forum to submit a query. Problem: See NOTE: The reference to weight "D" in the second line is incorrect. My Attempt: Step 1: Since this is a constant acceleration situation, I calculated the angular acceleration = 3 cm * -4 cm/s/s Step...
  2. S

    Torque on barbell when angular momentum is not constant

    Homework Statement [/B] Consider a barbell with two equal masses m that rotates around a vertical axis z not passing through its center with angular velocity \vec{\omega}. The barbell is forced to stay in this position by an appropriate support. Identify the forces exerting torques on the...
  3. L

    Falling rotating sphere and displacements

    Homework Statement Homework Equations How to locate the point P and C after 0.5s from their initial position ? The Attempt at a Solution Well i don't know whether it would be correct way to start the problem i.e find the centripetal acceleration .
  4. L

    Orthonormal basis of 1 forms for the rotating c metric

    Homework Statement Write down an orthonormal basis of 1 forms for the rotating C-metric [/B] Use the result to find the corresponding dual basis of vectorsSee attached file for metric and appropriate equations The two equations on the left are for our vectors. the equations on the right...
  5. JulienB

    Rotating bar hanging on a spring (oscillation)

    Homework Statement Hi everybody! I'm trying to solve a basic problem about oscillations, but I struggle to get everything together when it comes to the differential equation...I hope someone can help me to understand it better :) A thin bar of mass m and length l is pivotable about its...
  6. L

    Optimal Width of a rotating wheel

    Given this setup note: i just created arbitrary values if it helps, if not working with variables to find a general solution works fine too I am trying to find what the optimal width(would look like depth in the photo) of the wheel would be to generate the most power. I am stumped on how to...
  7. S

    Rubber on a rotating disk (angular velocity, forces)

    Homework Statement We place a rubber on the edge of a rotating disk. What forces act on the rubber? At what angular velocity, why and in what direction will the rubber fly off the disk? Homework Equations http://images.tutorvista.com/cms/formulaimages/83/angular-speed-formula111.PNG The...
  8. RicardoMP

    Rotating Cone and instantaneous axis of rotation

    Homework Statement Hi! I'm trying to solve a simple problem of mechanics, but I'm getting the wrong results and I suppose I don't yet grasp the concept of instantaneous axis of rotation very well. So, a cone (see attached picture) is rolling without slipping on a plane. Vp is point P linear...
  9. I

    Helicopter Winch - Rope Arranger About Rotating Cylinder

    hi, i am an aeronautical engineer student in need of some ideas for my groups mechanical design project. our project is to design a helicopter winch/hoist that meets the following requirements: 1. is atleast 150ft long 2. max 350kg load at a rate of 3ft/sec 3. (deeper into design) has a safety...
  10. P

    Terminology for rotating shaft with blades?

    Technical terminology: what’s it called? A cylindrical shaft which rotates in a fluid medium and carries a set of radially-arranged blades (?splines) attached by hinges. The blades fold flat against the shaft when it rotates in one direction (say clockwise) but they sweep out automatically to...
  11. D

    Rotating Coil in Magnetic Field

    Homework Statement [/B] Magnetic field values are often determined by using a device known as a search coil. This technique depends on the measurement of the total charge passing through a coil in a time interval during which the magnetic flux linking the windings changes either because of the...
  12. D

    Magnetic Field of Rotating Coil

    Magnetic field values are often determined by using a device known as a search coil. This technique depends on the measurement of the total charge passing through a coil in a time interval during which the magnetic flux linking the windings changes either because of the motion of the coil or...
  13. C

    B-field to create average emf in rotating coil

    Homework Statement A 0.300 m radius, 487 turn coil is rotated one-fourth of a revolution in 4.17 ms, originally having its plane perpendicular to a uniform magnetic field. (This is 60 rev/s.) Find the magnetic field strength needed to induce an average emf of 10,000 V.[/B]Homework Equations E...
  14. M

    Predicting Peak Displacement in Imbalanced Rotating Drum

    If I am attempting to prevent a suspended motor-rotating imbalanced drum of high mass from colliding with its enclosure, how can I attempt to predict the maximum displacement from a balanced center of rotation if I have only a single sensor that can accurately measure(1000 samples/sec)...
  15. K

    Why Is Normal Force Not Equal to mg in Rotating Collar Problems?

    Homework Statement Homework Equations [/B] Radial and Transverse coordinates to relate acceleration Balancing forces The Attempt at a Solution I know that there is more to this problem, but my question is simple: Why don't we know what the normal force is? When I solved it myself I...
  16. J

    How Do You Calculate the Velocity of a Point on a Rotating Disc?

    Homework Statement Find the velocity v of a general point on a plate rotating at 800 rpm which is r meters from the center. This is literally a copy and paste job. Homework Equations period = T = 1 / f ; f = frequency The Attempt at a Solution This is what I did please tell me if it is...
  17. Titan97

    Is moment of inertia only for rotating objects?

    Homework Statement A rod attached to a ceiling at one end and a disc on the other end is performing SHM. In case (1) the disc cannot rotate. In case (2) the disc can rotate about its centre. Compare the restoring torque and angular frequency in both cases. Homework Equations...
  18. Spinnor

    How do you perceive these lines to be rotating?

    In graphs c, d, e, and f below the red and blue pair of lines appear to be rotating about the horizontal axis. I'm curious how these graphs appear to others. When the lines are at the top do they appear to move towards or away from you? Thanks for playing! To me the top parts at first appeared...
  19. W

    Rotating disc of radius R spinning at constant angular velocity

    Ok, so here's the deal. I'm working on something that I SHOULD know the equations for after 5 years of school and a degree in mechanical engineering, but then again I can't remember why I walked into a room most times. So if ya'll could give me some guidance and at least a starting point I...
  20. kostoglotov

    System of ODEs in a rotating coord. system

    Homework Statement imgur link: http://i.imgur.com/pb14Q4Q.png Homework EquationsThe Attempt at a Solution [/B] The thing I don't understand is where the first two terms of each 2nd order ODE came about. I understand that they are there because the coordinate system is rotating, but when...
  21. Feodalherren

    Dynamic systems: two rotating disks interconnected by damper

    Homework Statement Homework EquationsThe Attempt at a Solution So I'm assuming my solution is just as valid as the one in the book, if not, can somebody explain to me why? I prefer my solution since they say that phi is a known function.
  22. B

    Centrifugal acceleration in rotating frame

    Homework Statement I have a doubt about the way to calculate the centrifugal acceleration for a point P that rotates with angular velocity ##w_1## wtr a inertial frame on a platform that rotates with angular velocity ##w## (##w_1>w)##. I want to find the centrifugal acceleration in the...
  23. E

    Metrics: Stationary & Rotating - Can They Coexist?

    Can metrics be stationary and rotating at the same time? Doesn't stationary here means that the metric is time-independent. Thus, if a metric is time-indepedent how could it be rotating?
  24. C

    Rod rotating about pivot with spring

    Homework Statement Consider the following classic problem: we have a rod in the vertical position with a pivot at its midpoint and a spring attached to the bottom of the rod, perpendicular to the rod. The is rotated through a small angle theta to the vertical, and released. Find the period of...
  25. akshay86

    Rotating & Moving Spheres: What Causes Torque & Force?

    if a central force acts on a sphere it will rotate and move and also a angular momentum is given to that body it will also move in the same manner.What provide torque in first case and net force in second case.is it friction then how?
  26. deuel18

    Rotating Stator: Permanent Magnets & Rotor Polarity Change

    Hello. I just want to know if it is possible to have permanent magnets as Stator in a Rotating Magnetic field morot. However, these Stators rotates to change their polarities in relation with the Rotor. Much like the harmony of Intake/Exhaust valves in an Internal Combustion Engine.
  27. Anakratis

    Upward force due to rotating magnetic field

    Hey guys, So I have a bit of an interesting problem to solve here. I'm trying to calculate the upward repulsion force due to eddy currents created in a conductive surface by a rotating magnetic field. I'm doing this for an undergraduate lab project, and want to be able to provide quantifiable...
  28. NihalRi

    Effect of rotating polarizer on intensity of transmitted light

    Homework Statement Plane polarised is incident normally on a polerizer which can rotate in plane perpendicular to light. The intensity of of incident light is 8W[m][/-2] and transmitted intensity is 2W[m][/-2] if polerizer is rotated 90 deg what is the new transmitted intensity Homework...
  29. G

    MHB Volume enclosed by rotating a curve segment

    The volume enclosed by rotating the segment of the curve $y = \frac{1}{2}|x-1|$ between $x = 0$ and $x = 2$ about the $x$-axis is equal to: Is it this simple? Since $x \ge 0$ it's $\frac{\pi}{2} \int_0^2 (\sqrt{(x-1)^2})^2\, dx = \frac{\pi}{3}.$
  30. P

    Tension, centrifugal force, two objects rotating

    Homework Statement [/B]there's an image of the situationHomework Equations [/B]F= mω^2 RThe Attempt at a Solution [/B]so, in the image there are two spheres that exerts a tension on the string using their centrifugal, since the centrifugal bodies are two I expect that the tension is the sum...
  31. sergiokapone

    Metrics of rotating sphere in GR

    Homework Statement A thin spherical shell of radius ## R ## rotates with angular velocity ## \Omega ##. Its total mass ## M ## is uniformly distributed. Find metric inside and outside the shell, assuming its small departure from the flat space-time. Find the angular velocity ## \omega ##...
  32. A

    Electromagnetic induction by a rotating sphere

    Homework Statement http://physics.columbia.edu/files/physics/content/Quals2010Sec2.pdf Problem 1 Consider a rigid, ideally conducting sphere of radius R, with total charge zero. The sphere rotates with angular velocity Ω, ΩR<<c. Suppose a dipole magnetic field threads the sphere. the dipole is...
  33. T

    Hexagon's rotating in a larger hexagon

    Hello The attached diagram shows a group of 6 hexagons rotating inside a larger hexagon. I have never seen such rotation before and didn’t envisage it until I drew it. Just out of curiosity I was hoping someone could advise of any documentation on such rotation. I cannot see any substantial...
  34. G

    I Energy of a Rotating Binary system

    - We have two identical point masses, they are moving in uniform circular motion and in the same plane. - Both masses are 180 degrees out of phase, they are always on opposite ends of their circular path. -The "orbit" radii for both masses are the same.We consider only SR effects, no GR.Now we...
  35. E

    Torque of rotating coaxial cylinders with gas between them.

    I was going through a worked example in book "Concepts in Thermal Physics" by S.J. Blundell and K.M.Blundell. The example talks about measuring viscosity of a gas between two coaxial cylinders. Homework Statement Two vertical coaxial cylinders. Outer cylinders is rotated by a motor at constant...
  36. M

    Rotating Disc with central hole

    Homework Statement Problem and worked Example[/B] Homework Equations In worked example 1. Problem The Attempt at a Solution It's the part where I'm subtracting one stress from the other stress. I put it in parenthesis on the worked example. I don't think my method here is right, I've tried...
  37. R

    Static friction rotating discs

    Hi everyone This is my first post on the forum. I work in engineering and use this forum to answer questions from time to time. I am looking for confirmation of my understanding of static rotation torque (not something I deal with in day to day work). Imagine 2 identical discs or washers that...
  38. T

    Derivation of acceleration in rotating coordinates

    I was just trying to write out the derivation for an object's trajectory from an inertial coordinate system if the object is rotating in another coordinate system (e.g. finding Coriolis, centrifugal acceleration). I seem to have gotten something close to what I was looking for, but after...
  39. R

    Load rotating device - will it slide?

    Homework Statement I'm designing a device for changing a load position from vertical to horizontal. It has a wheeled frame (2) which allows an operator to transport the load after reorientation. The combined centre of gravity of a rotating platform (1) and the load moves forward due to...
  40. T

    Rotating platform on top of another rotating platform

    Homework Statement Have platform A that is being spun by a centrifuge with a radius R1 and centripetal velocity of w1. On top of platform A is a Lazy Susan (Platform B) that spins about a radius R2 with a centripetal velocity of w2. There are accelerometers placed on the the purple platform...
  41. M

    Surface of a rotating liquid

    Homework Statement A cylindrical container of water with a radius of 6.0 cm is placed on a phonograph turntable so that its outer edge just touches the outer edge of the turntable. The radius of the turntable is 14.5 cm, and the turntable rotates at 33 and a 1/3 revolutions per minute. How much...
  42. faradayscat

    Dynamics/kinematics of rotating sphere

    I'm wondering about how one would describe the dynamics of a rotating sphere. Consider this: a solid sphere of mass "m" and radius "r" is set to rotate about a tangent to its surface. If it is released from the horizontal position such that it swings like a pendulum, what would be the force...
  43. sergiokapone

    Can a rotating dielectric disc be polarized?

    Can a rotating dielectric disc be polarized? No external electric or magnetic field .
  44. C

    Torque of charged rotating disc in uniform magnetic field

    Hi, I'm having an issue with finding a starting point for the following problem. I've looked through my magnetism and electrodynamic notes but was unable to find a starting point. Could someone please help direct me on the correct path? Thank you. Homework Statement A thin circular disc of...
  45. J

    Maximum height of CM of a rotating stick

    Homework Statement [/B] A uniform stick is held horizontally and then released. At the same instant, one end is struck with a quick upwards blow. If the stick ends up horizontal when it returns to its original height, what are the possible values for the maximum height to which the center...
  46. Nathanael

    Particle free to slide along a frictionless rotating curve

    Homework Statement A particle (of mass m) is free to move along a frictionless curve y(x) which is rotating about the y-axis at a constant angular speed ω. A uniform gravitational field (of strength g) acts along the negative y direction. Find the equation of motion of the particle. (That's...
  47. A

    Sliding Rod and Rotating Disc Question

    Homework Statement A uniform rod AB of length L and mass m1 is connected by a pin joint to the center of a uniform disc of radius R and mass m2. The system is placed in a vertical plane (as shown in Figure 2) and released from rest with θ=45°. (a) Draw the free-body diagrams for the rod and the...
  48. J

    Speed of an object in a rotating frame

    Is it meaningful to measure the speed of an object in a rotating frame, and if so how do you do it in the following case? Consider a rim of circumference 100 rotating at 0.8c, both measurements with respect to the inertial lab frame. An object is at a point on the rim with a standard clock...
  49. kontejnjer

    How Does Fermi Transport Describe a Gyroscope's Motion on a Rotating Disk?

    Homework Statement Describe the motion of a gyroscope with center of mass fixed on a rotating disk in coordinates of an observer which is at rest on the disk in the absence of gravity. Homework Equations The hint given was to somehow use Fermi transport, so I'm guessing: \mathbb F_u X=\nabla_u...
  50. artriant

    Calculate Wire Tension in Zero Gravity Circle | Rotating Wire

    Hello this is my first question here :) So here is my problem: We have a circle radius 50 (m), made out of iron wire mass 5.506206591207348477884587 Kg per meter of rope. Rope diameter 11/8 inces or 3.4925cm The wire rotates with 3 rpm in zero gravity 1)How can i calculate the tension? Thx...
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