What is Rotational motion: Definition and 610 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. A

    What is the direction of hinge force?

    how to find direction of hinge force? for example ,if a disc is hinged at a point on it's circumference and is exhibiting a rotational motion due to gravity,what is the hinge force?
  2. A

    How a rotational motion could be in an inertial ref. frame

    When rotation exists, so does the radial acceleration. It can be defined as ar=-ω2xr So there is a kind of acceleration with rotation all the time. Thus, we have to use non-inertial reference frame all the time. Could a rotational movement be analysed in an inertial ref. frame?
  3. A

    Calculating Angular Momentum: Axis of Rotation Explained

    about what axis is equation of angular momentum calculated(angular momentum = moment of inertia*angular velocity)? please help.
  4. A

    How to Calculate the Moment of Inertia for a Half Disk System?

    in this video http://www.physicsgalaxy.com/lectures/1/44/234/Solved-Example-2#12(see only the question) the method illustrated is integration but i thought of an alternate method, moment of inertia of half disc with radius r2 is 1/2mr2^2 and that of half disc with radius r1 is 1/2mr1^2.so...
  5. H

    Rotational Motion: Calculating Time to Reach 750 RPM

    Homework Statement A 1.5 hp motor drives a machine disk having a mass of 4.5 kg and a diameter of .4 m from rest to a speed of 750 rpm. How long does it take to reach the operating speed? Homework Equations angular momentum torque The Attempt at a Solution I'm not really sure where to start...
  6. D

    Rotational motion homework help

    Homework Statement A uniform, solid sphere of mass 350 grams and radius 25.0 cm has an axle attached to it tangent to its surface. The axle is oriented horizontally, causing the sphere to be suspended below it, its center of mass directly below the axle. Someone lifts the sphere until its...
  7. P

    Rotational motion of a door on a moving car

    1. A car door is left open at an angle theta with the side of the car. The door is uniform of mass M and length L. The car accelerates with linear acceleration a. How long does it take the door to close. 2. theta = .5(angular acceleration)t^2 angular acceleration = tangential...
  8. Mr Davis 97

    Difference between circular motion and rotational motion

    I don't really understand the difference between uniform circular motion and rotational motion. I know that uniform circular motion deals with a body that is orbiting around a central point, with a centripetal force that is causing it to move in a circle. I know that rotational motion uses...
  9. faradayscat

    Dynamics/kinematics of rotating sphere

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  10. A

    Increasing speed by decreasing intertia?

    Just curious, explanation if youre going to answer please! 2 horizontal disks stacked on one another spinning at constant v, (about a frictionless axis perpendicular to their center), both have mass. Okay, so let's say its possible to instantaneously remove the top disk. So would that make...
  11. C

    Rotational Motion: Solving Baseball Throw Homework

    Homework Statement A baseball is thrown at 85 mph and is thrown with a spin rate of 125 rpm. The distance between the pitchers point of release and the catcher’s glove is 60.5 feet. How many full turns does the ball make between release and catch? Homework Equations Vf^2=V0^2+2a(Δ x) X=...
  12. 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...
  13. 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...
  14. 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...
  15. 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...
  16. 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=...
  17. 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...
  18. 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...
  19. D

    Banked Curve - Minimum Turn Radius

    Homework Statement A car traveling 10 m/s is moving along a track banked at 5 degrees. The tire-road friction coefficient is .3 What is the minimum radius it can travel without slipping? v0= 10 m/s Bank Angle Θ = 5° μ=0.3 Note I am working through prep material for the exam. The solution...
  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. 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...
  23. 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.
  24. 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...
  25. **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...
  26. 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...
  27. E

    Rotational motion-why are torques not in opposite directions

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  28. A

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    The attached file contains a question my brother asked me solve. But this problem might have some problem of its own. I feel like every position of the spanner is a probable one. Can someone please help. p.s. i know the answer but avoiding giving it to avoid getting biased.
  29. 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...
  30. 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...
  31. P

    Rotational motion - finding tangential acceleration

    1. The problem A 6 kg block is released from a height of 5 m on a frictionless track and goes into a half pipe with a radius of 2 m. Determine the tangential and radial components of the acceleration when the block reaches a height of 2 m.Homework Equations Ac= v^2/r. At = r*angular...
  32. L

    Relating SHM and Rotational Motion

    Homework Statement A spring of stiffness k is attached to a wall and to the axle of a wheel of mass m, radius R, and moment of inertia I = βmR^2 about its frictionless axle. The spring is stretched a distance A and the wheel is released from rest. Assume the wheel rolls without slipping. At...
  33. J

    How Do You Calculate Angular Acceleration from RPM?

    A 61 cm diameter wheel accelerated uniformly about its center from 120 rpm to 280 rpm in 4.0 seconds. Determine the Angular acceleration So I converted the 120 and 280 rev per min to radians per s with 45238.93 rad/s and 105557.51 rad/s and used them as angular velocity final and initial. then...
  34. L

    Centrifugal Force: Earth Rotation & Its Effects

    We know that the Earth is rotating, and its gravitational force is the centripetal force. So if I'm standing on the Earth, I'll feel 3 forces: Gravitational force, normal force and centrifugal force. However, the magnitude of the centrifugal force is equal to the gravitational force, so wouldn't...
  35. Y

    Moment of inertia and rotational motion

    Hello, I am currently attempting to cover rotational motion using Halliday's Fundamentals of Physics. I understand very well the concept of moment of inertia as defined as the sum Σmi*ri2. However, the textbook argues that if there are too many particles, the moment of inertia can be defined as...
  36. CaptCoonoor

    Rotational Motion - Disk-Disk Collision problem

    Hey Guys, Can you tell me how to solve this one, Need not give me direct answers but just take a look at this : Consider two disks A and B of equal radius, let m1 be the mass of disk A and m2 be the mass of disk B, Both are moving towards each other with Velocity v1 and v2 respectively, If they...
  37. M

    Rotational Spring Arbitrary Motion

    What I want to do is model the rotational behaviour of two bodies (1 and 2). They are connected by three virtual rotational springs (representing a link between them). For a normal (translational) spring the forces on body 1 in X, Y, and Z would be easily calculated as: $$ \mathbf{F}_1 =...
  38. S

    Rotational Motion - Conceptual

    Homework Statement The lightweight pivoted bar in the figure will be in rotational equilibrium when a 200N force acts (a) down at D (b) up at B (c) down at E or up at C (d) up at C only (e) none of these Homework Equations Torque = Force x Distance ∑Torque= 0 for rotational equilibriumThe...
  39. minimario

    Angular Momentum: Puck Spinning

    Homework Statement The puck in the figure shown below has a mass of 0.120 kg. Its original distance from the center of rotation is 40.0 cm, and it moves with a speed of 80.0 cm/s. The string is pulled downward 15.0 cm through the hole in the frictionless table. Determine the work done on the...
  40. H

    A wheel with rotational inertia I = 1/2MR^2

    Homework Statement [/B] A wheel with rotational inertia I = 1/2MR^2 about its horizontal central axle is set spinning with initial angular speed W0. It is then lowered, and at the instant its edge touches the ground the speed of the axle (and CM) is zero. Initially the wheel slips when it...
  41. H

    The 1100 kg mass of a car includes four tires

    Homework Statement The 1100 kg mass of a car includes four tires, each of mass (including wheels) 35 kg and diameter 0.80 m. Assume each tire and wheel combination acts as a solid cylinder. If the car is initially at rest and is then pulled by a tow truck with a force of 1500 N, what is the...
  42. J

    Introductory Rotational Motion Question

    I'm beginning the chapter of Rotational Motion and Angular Momentum and it says the following which got me confused: Source: http://cnx.org/contents/031da8d3-b525-429c-80cf-6c8ed997733a@8.32:68/College_Physics When I was introduced acceleration at the beginning, it was stated that an...
  43. K

    Rotational motion -- Energy stored in a flywheel

    Homework Statement Cylindrical shape pulley ( m = 6 kg, R = 0.18 m) is rotating at a frequency f = 10 s-1. Due to constant torque it stops. Calculate the work done by the breaking force. Homework Equations w = 2πf The Attempt at a Solution [/B] I can calculate the angular velocity: w = 2πf =...
  44. K

    How does rotational motion contribute to an object's total kinetic energy?

    Homework Statement Same mass sphere and cylinder are rolling on a horizontal plane. Which part of each objects kinetic energy does objects rotational energy make up? Homework Equations Erotational = 1/2 Iw2 Ekinetic = 1/2 mv2 The Attempt at a Solution [/B] I know, that moments of inertia...
  45. T

    What is the required torque for a spinning flywheel?

    Hello, I would like to know the amount of torque required when the flywheel starts? I know that once at speed the flywheel doesn't require torque. I would also like to know what size of slip ring induction motor to run as the below mentioned speed. The weight of the flywheel is= 6500 kg ( wt...
  46. L

    How Do Two Connected Discs with Masses Affect Angular Acceleration?

    Homework Statement Two discs of radius R and r are fixed to each other, i.e., they rotate together. Strings are wound around both discs and two equal masses M are connected to the ends of the strings (see Figure 1). Find the angular accelerations of the discs, the accelerations of the masses...
  47. B

    Angular Acceleration of a Wheel on a Turntable

    Homework Statement [/B] The axle of a wheel is mounted on supports that rest on a rotating turntable. the wheel has angular velocity ##\omega_1 = 44.0\; \frac{\textrm{rad}}{\textrm{s}}## about its axle, and the turntable has angular velocity ##\omega_2 = 35.0\; \frac{\textrm{rad}}{\textrm{s}}##...
  48. minimario

    Block Around a Track: Find Force & Coeff of Friction

    Homework Statement A small block of mass m = 0.50 kg is fired with an initial speed of v0 = 4.0 m/s along a horizontal section of frictionless track, as shown in the top portion of Figure P7.58. The block then moves along the frictionless, semicircular, vertical tracks of radius R = 1.5 m. (a)...
  49. O

    Rotational motion- potential and kinetic energy

    http://i.imgur.com/0RtN9Ui.png?1 I am trying to find the linear velocity of the sphere as it leaves the cliff. 2. Homework Equations : Moment of inertia of a sphere: I= 2/5 mr2 3. My attempt at a solution: I know that I am supposed to solve this through the conservation of energy, but would...
  50. W

    An experiment question: Rotational Motion

    Homework Statement I am doing the rotational motion experiment with a rotary disk that has three spindle sizes. A string goes around the spindle and is connected to a hanger. I calculated my ratio as a percentage of total final KE to decrease in potential energy and it comes out to be around...
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