What is Rotational: 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. S

    Help with spring rotating around its axis of rotational symm

    Homework Statement An astronaut on a spacewalk loses her grip on a circular garter spring (pictured below). Looking at the spring she notices that it is rotating around its axis of rotational symmetry at a rate of 300 rpm. The circumference of the rotating garter spring is 1% longer than that...
  2. H

    Bicycle wheel rotational motion

    1. Homework Statement A guy is riding a bicycle, and we consider the front wheel, which has mass M, radius R and for the purpose of the moment of inertia can be thought of as a uniform disc. a) When the bike is going with linear speed v, what is the magnitude and direction of the angular...
  3. H

    Rotational Motion of the Yo-Yo

    1. Homework Statement A yo-yo roughly speaking consists of two round, uniform discs, sandwiched around a third smaller disc. A string is wound around the middle disc, and so the yo-yo may roll up and down as the string winds and unwinds. Consider such a yo-yo, with the two bigger discs...
  4. L

    What is the rotational velocity of the crank?

    Homework Statement You accidentally knock a full bucket of water off the side of the well. The bucket plunges 13 m to the bottom of the well. Attached to the bucket is a light rope that is wrapped around the crank cylinder. The cylinder has a radius of 0.085 m and inertia of 4.0 kg. The inertia...
  5. D

    How Does Non-Pure Rolling Differ from Pure Rolling in Rotational Dynamics?

    Question: Refer to https://www.physicsforums.com/threads/rolling-motion-of-plank-and-cylinders.93329/ I am able to understand all the points until the point v_roller+rω=v_plank. I have a tough time understanding this part. My attempt at the question: I think that the static friction at the top...
  6. MattyAB

    System for turning Rotational into Linear movement

    Hey Everyone, I want to build a Laser cutter for myself from scratch (sort of). I need some way of turning the rotational energy of the servo into a linear movement. I want something fairly cheap, so nothing to pricey. I thought of the classic Lego style thing, with a gear on the servo, with a...
  7. B

    Rotational Forces on a Hollow Cylinder

    Homework Statement I am trying to model a hollow cylinder of known radius r, length l and density rho. The cylinder is fixed on a horizontal axle along its longest axis (l) and will have a force F applied tangentially to its surface and perpendicular to its axis, with negligible frictional...
  8. K

    Calculating Rotational Inertia of a Disk with Mass M and Radius R

    If there is a disk of mass M and radius R that is already rotating, then someone puts a block with mass m on it a meters away from the center of mass. What is the rotational inertia then? Is it I=(M+m)R^2?
  9. snacksforsale

    How does rotational motion influence static friction?

    I apologize in advance for not exactly adhering to the template, but the question I have here arose from my attempts to solve the following exercises, so please bear with me. (Edit: I also apologize if discussion of a concept belongs in a different forum, as this is not exactly a homework...
  10. P

    Rotational Motion: Energy and Momentum Conservation

    Homework Statement A child with mass m is standing at the edge of a merry go round having moment of inertia I, radius R and initial angular velocity x as shown. (The figure shows a disc moving anticlockwise, with the velocity v (Mentioned at the end) pointing upwards to the right most edge of...
  11. K

    Rotational Acceleration of an Amusement Park Carousel

    Homework Statement Moving at its maximum safe speed, an amusement park carousel takes 12 s to complete a revolution. At the end of the ride, it slows down smoothly, taking 3.5rev to come to a stop. What is the magnitude of the rotational acceleration of the carousel while it is slowing down...
  12. Abhirikshma

    Dependence of rotational angular velocity of planets

    On exactly what factors does the rotational angular velocity of a planet depend ? Can a mathematical expression be derived for it ?
  13. F

    Does relativistic QM obey rotational symmetry?

    SO(3) is subgroup of Poicare group.Does Relativistic Quantum Mechanics obey rotational symmetry.If it is,why we do not still keep the non-relativistic concept of angular momentum(orbit angular momentum plus spin) for relativistic concept of angular momentum,but we instead replace the concept by...
  14. E

    Rotational motion, find the frictional force.

    Homework Statement A small 350-g collar C can slide on a semicircular rod which is made to rotate about the vertical AB at a constant rate of 7.5 rad/s. The coefficients of friction are μs = 0.25 and μk = 0.20. Homework Equations Tangent Velocity= Radians*radius Normal acceleration an=...
  15. C

    Rotational Motion - Centripetal force

    Homework Statement A hump backed bridge is in the form of a circular arc of radius 35m. What is the greatest speed with which a car can cross the bridge without leaving the ground at its highest point? Homework Equations F = m v2/r = mrω2 The Attempt at a Solution I've tried using the equation...
  16. Z

    Finding the Horizontal Force on a Bracket Supported by a Single Screw

    Homework Statement One side of a plant shelf is supported by a bracket mounted on a vertical wall by a single screw. Ignore the weight of the bracket. Find the horizontal component of the force that the screw exerts on the bracket when an 80.0 N vertical force is applied as shown Homework...
  17. Z

    Solving rotational motion without torque

    Homework Statement A potter’s wheel—a thick stone disk of radius 0.500 m and mass 100 kg—is freely rotating at 50.0 rev/min. The potter can stop the wheel in 6.00 s by pressing a wet rag against the rim and exerting a radially inward force of 70.0 N. Find the effective coefficient of kinetic...
  18. amjad-sh

    Rotational inertia: a contradiction?

    We know that the rotational inertia I of a certain object is I =∫r∧2 dm where r is the distance between the axis of rotation and the increment of this object that carries a mass dm. What confuses here is the following: Take for example a hoop of mass M and radius R. Integration theory gives...
  19. S

    Virtual Work & Quadcopter Torques: Exploring Rotational Dynamics

    Here is what we know from virtual work: $$ \delta W=\sum_{i=1}^N{\vec F_i\cdot\delta\vec r_{i}} $$ Where ##N## is the number of bodies in the system. I am considering a quadcopter, modeled as a rigid body so it is just one body and we have: $$ \delta W=\vec F\cdot\delta\vec r $$ My question...
  20. andyrk

    Gear Ratio in Bicycles using Rotational Motion

    When we change the gears of the bicycle we are riding, we change the the disc we are currently at (which are located at the place where we pedal) to some other disc. This means the radius of the circular disc we were pedaling/rotating changes. So that means if we were rotating the disc with...
  21. A

    Rolling Motion of Ring, Disk, Sphere: tr<td<ts

    1. A ring , a disk and a sphere all of same mass and radius, with moments of inertia Ir, Id, Is respectively about their axes, roll down without slipping on an inclined plane from a given height. If the time taken for the ring, disk and sphere to reach the bottom of the plane are tr, td and ts...
  22. J-dizzal

    Rotational inertial and energy.

    Homework Statement The figure shows a rigid assembly of a thin hoop (of mass m = 0.25 kg and radius R = 0.13 m) and a thin radial rod (of length L = 2R and also of mass m = 0.25 kg). The assembly is upright, but we nudge it so that it rotates around a horizontal axis in the plane of the rod and...
  23. Vaibhav DixiT

    Rotational Spectra of Diatomic Molecules

    I was wondering how Rotational Spectra of diatomic molecule can be related to Heisenberg Uncertainty principle (Qualitatively). Being a QM model where rotational energies are quantized, there should be a qualitative reasoning on lines of the uncertainty principle, right? Anyone can direct me to...
  24. rpthomps

    Rotational Inertia of a triangle

    Homework Statement A thin, uniform vane of mass M is in the shape of a right triangle, as shown. Find the rotational inertia about a vertical axis through its apex, as shown in the figure. Express your answer in terms of the triangle’s base width b and its mass M. Homework EquationsThe...
  25. rpthomps

    Rotational Motion Final Angular Speed Calculation

    Homework Statement An object of rotational inertia I is initially at rest. A torque is then applied to the object, causing it to begin rotating. The torque is applied for only one-quarter of a revolution, during which time its magnitude is given by \tau =Acos\Theta , where A is a constant and...
  26. A

    What forces are involved with Earth's rotational bulge?

    I'm trying to understand mathematically, if possible, why it is that the Earth bulges at the equator as a result of its rotation and how exactly gravity manages to keep it all together. Would the better approach be to keep myself in a rotating frame of reference? I lack some knowledge of...
  27. Shahryar

    Clockwise direction rotational motion in MCS Adams software

    I am working on a simulation but i want to put a constraint that my shaft rotates clockwise only, If a force is applied on anti clock wise direction, it doesn't go back. Working on MSC adams software. Thank you in advance for any kind of advice anyone can help with.
  28. DameLight

    Rotational ACC and Gravitational ACC

    solved thank you : ) 1. Homework Statement A bucket of water of mass 14.2 kg is suspended by a rope wrapped around a windlass, that is a solid cylinder with diameter 0.350 m with mass 12.8 kg . The cylinder pivots on a frictionless axle through its center. The bucket is released from rest at...
  29. K

    Calculating angular speed of a ball after collision

    Hi, I've been wondering is there anyway of calculating the angular speed of a ball after there is a collision of it and another mass. For example a baseball bat hitting the ball. I have not looked up on angular momentum, but is angular momentum involved in this? Based on common sense, I think...
  30. jason lee

    Acceleration of system, connected to a rotational body

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > I have a problem here. what's the formula for the acceleration of a system wherein. A disk with a cylinder on top of it with a shaft underneath to wound the thread to connect it with a pulley...
  31. J

    Translational Motion Vs. Rotational Motion

    Howdy. It has become clear to me that translational motion is not taken into account in general relativity because it is subjective, and that rotational motion is taken into account in GR in places such as the Kerr Metric. What makes rotational motion so absolute? Couldn't an observer's...
  32. T

    Can someone check my answer to a rotational problem?

    Homework Statement A stick of length L and mass M is in free space and not rotating. A point mass m has an initial velocity v heading in a trajectory perpendicular to the stick. The mass collides and adheres to the stick a distance b from the center of the stick. Find the resulting motion of...
  33. T

    Whats the equation for rotational momentum?

    Homework Statement I'm confused with when to use L=Iw (inertia times angular speed) for momentum and when to use L=rxP (r cross p) for inertia. Can someone please explain to me what each one is? Homework Equations Just a conceptual question. The Attempt at a Solution Just a conceptual question.
  34. B

    Do rotational degrees of freedom contribute to temperature?

    I cannot find a simple answer to this question anywhere. What degrees of freedom contribute to the temperature of a gas? Let's say we have a box of ideal gas. The temperature is the average kinetic energy of the particles and only includes translational degrees of freedom: velocity. Now...
  35. P

    How do I find rotational energy for a pulley system?

    Homework Statement So I have a horizontal pulley positioned at the edge of table with a mass of .2kg hanging down from a height of .76meters, the other end of the string is attached to a wooden block of mass .25kg that when the .2kg weight is dropped the wooden block is pulled towards the...
  36. N

    Rotational kinematic need explanation

    ice skater with mass = 80 kg moment of inertia (about her central axis) 3 kg m2. Catch baseball with outstretched arm 1m from her central axis. Ball has mass 0.3 kg and v0 = 20 m/s before the catch. V system ( skater + ball ) after catch = 0.0747 m/s Question : b. Angular speed of the...
  37. D

    Radians and the unit of rotational energy

    Hello everyone I have a question regarding radians and the unit of rotational energy (which has been probably asked several times elsewhere but is still confusing for me :-) ). As I understand radian (rad) is a UNIT that is dimensionless (thus cannot be omitted), correct ? Now if I want to...
  38. M

    Rotational equilibrium equation - Moment of Forces (2D prob)

    Homework Statement The landing gear of an aircraft is composed of a main leg OA (with a weight including the wheel is 1000N to G) and two secondary links BC and 50cm long each CD. The DC link forms an angle θ of 30 degrees with the vertical. a) Add the rotational equilibrium equation with...
  39. C

    CMB , Spherical Harmonics and Rotational Invariance

    In Dodelson's "Modern Cosmology" on p.241 he states that the ##a_{lm}##-s -- for a given ##l##-- corresponding to a spherical harmonic expansion of the photon-temperature fluctuations, are drawn from the same probability distribution regardless of the value of ##m##. Dodelson does not explain...
  40. **Mariam**

    Rotational motion: air puck revolving Is it possible?

    question here Hello, this isn't really a homework question as I understand how to solve it. But just out of curiosity, is it possible for this to actually be set up in real life and for the 1 kg mass to be in equilibrium? because when I imagine such a situation I feel that the revolving puck...
  41. P

    Rotational motion thought experiments

    So say we have a stick in space with the CM in the middle and we apply two forces of equal magnitude and direction over the same time, one force at the CM, and the other at some distance away from the CM. Ideas: 1. One would obtain just translational motion the other would have both...
  42. E

    Rotational motion-why are torques not in opposite directions

    Homework Statement A cylinder of mass m is suspended through 2 strings wrapped around it at its ends, connected to the ceiling. Both strings have equal tension, and the cylinder rolls without slipping. r is the distance between the CM of the cylinder and each end. I is the moment of inertia of...
  43. P

    Conceptual question about torque

    Homework Statement This is a conceptual question about a prior assignment I had: A thin spherical shell rolls down an incline without slipping. If the linear acceleration of the center of mass of the shell is 0.23g, what is the angle the incline makes with the horizontal? Homework Equations...
  44. E

    Rotational motion -- Ball rolling back and forth on a U-shaped ramp

    If a ball rolls down a U-shaped ramp from a height h, why does it not reach a height h on the other side? (Frictionless ramp) It will reach a height of (5/7)*h, but I'm not sure why. Some of the potential energy is converted to rotational and some is translational kinetic, but why do they not...
  45. Dustin11H3

    Need animation/video to convey rotational speeds

    Hello Everyone, I need an animation or video or something that will convey different speeds of different sized circles. Ideally, I would like some type of tire setup that shows a smaller circle driven at the same speed rotating more quickly than a larger circle. I am using this for an...
  46. goonking

    Calculating Rotational Inertia: Hoops vs. Solid Cylinders

    Homework Statement Homework EquationsThe Attempt at a Solution I assume the energy stored is = 1/2 (I) (ω^2) I (moment of inertia) is MR^2 since it's a hoop? or is it a solid cylinder? do we need to convert the rpm (revolutions per minute) to radians per sec?
  47. D

    Rotational Inertia of a Pulley System

    Homework Statement Homework Equations Kinetic Energy = 0.5 I w^2 v = r * w torque = Inertia * angular acceleration The Attempt at a Solution That's the problem. I have no idea where to start. I assume that the end goal is to find the angular velocity, and convert to linear velocity, but I...
  48. J

    Rotational spectrum assignment

    If I have the energy value (in cm-1) of a specific line in the rotational spectrum, how do I find out/assign the correct J''-J' values? I know the selection rules for J to be +/- 1 for each rotational transition but I'm not sure how you can correctly identify which J value it is if your only...
  49. F

    Do you consider both regular and rotational kinetic energy?

    Homework Statement If I have a ball moving in a circular path (ball is connected to a string), as shown in this picture: http://w3.shorecrest.org/~Lisa_Peck/Physics/syllabus/mechanics/circularmotion/Images/cent_force_on_ball.gif should I say that the energy of the ball is both its kinetic...
  50. Cliff Bryant

    Forces plus Rotational Motion

    Problem: "Two blocks of equal masses m are attached by an ideal string. One mass lies at radial distance r from the center of a horizontal turntable rotating with constant angular speed of 6 rad/s, while the second hangs from the string inside the hollow spindle of the turntable.The coefficient...
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