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. S

    Circular Motion, Center of Gravity, Rotational Motion Homework Help

    I was absent from school for 3 days and my teacher gave this worksheet to me. I have no idea what I'm doing on it. Can anyone please help me with this? Thanks.
  2. A

    Understanding Angular Momentum & Energy in Rotational Motion

    Suppose a man is holding his arms extended in with some masses in each hand. He is set rotating about a vertical axis . If he pulls his hands toward his stomach then according to law of conservation of angular momentum there is an increase in his angular velocity. Also there is a change in his...
  3. Wellesley

    Rotational Motion Find g - Inclined Plane

    Rotational Motion Find g - Galileo Inclined Plane Homework Statement Galileo measured the acceleration of gravity by rolling a sphere down an inclined plane. Suppose that, starting from rest, a sphere takes 1.6s to roll a distance distance of 3.00 m down a 20 degree inclined plane. What value...
  4. S

    Rotational Motion and linear accerlation

    Homework Statement A solid cylinder of weight 50 lb and radius 3.0 inches has a light thin tape wound around it. The tap passes over a light smooth fixed pulley to a 10 lb body hanging vertically in the air. If the plane on which the cylinder moves is inclined 30 degrees to the horizontal...
  5. R

    How Do You Calculate the Velocity of a Corner of a Falling Tilted Plate?

    Homework Statement A square plate is tilted on one of its corners as shown below. If the corner does not slip, and the plate is allowed to fall, determine the velocity of the moving corner before it hits the ground. The moving corner is point P, which is 45 degrees above the horizontal...
  6. Y

    Rotational motion and tangential speed?

    Homework Statement A 919 kg rollercoaster is about to go up a hill that acts as the top of a circle 16.21m in diameter. What is the fastest that car can move (in m/s) without leaving a track? known: mass: 919 kg diameter: 16.21 radius: 8.105 Homework Equations Vt=r\omega...
  7. J

    Rotational Motion - I have the answer but I don't know how to get there

    A torque of 1 N.m is applied to a bike wheel of radius 35 cm and mass 0.75 kg. Treating the wheel as a hoop (I=MR^2) A. What is it's angular acceleration? Answer - 10.9 rad/s^2 B. If the wheel starts from rest, what is its angular speed after 5 seconds? Answer - 54.4 rad/s C. How many turns...
  8. P

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  9. M

    Moment of inertia and Kinetic Energy (Rotational Motion)

    Homework Statement A skater spins with an angular speed of 8.3 rad/s with her arms outstretched. She lowers her arms, decreasing her moment of inertia by a factor of 8.9. Ignoring the friction on the skates, determine the percent of change in her kinetic energy. Answer in percent...
  10. M

    Kinematics of Rotational Motion

    Homework Statement A turntable that is initially at rest is set in motion with a constant angular acceleration α. What is the magnitude of the angular ve- locity of the turntable after it has made one complete revolution? Homework Equations w(omega)^2 = w(omegeInitial)^2 +2α(delta)θ...
  11. K

    Rotational motion question, can anyone check over this result please?

    Homework Statement An inextensible light string of length 2 m is fixed at one end A and carries at its other end B a particle of mass 3 kg, which is rotating in a horizontal circle whose centre is 1 m vertically below A. Find the angular velocity of the particle and the tension in the...
  12. G

    Rotational Motion: Meaning of ∫v(t)dt - ∫Rw(t)dt

    This is merely a simple, but conceptual, problem. Say we have a cue ball of mass M and Radius R rolling without slipping on the pool table. What is the the meaning of the ∫v(t)dt - ∫Rw(t)dt where w(t) is the angular speed of the pool ball. My guess is that this represents the length the ball...
  13. M

    How Do You Calculate Force and Work for a Suspended Spool in Rotational Motion?

    Homework Statement A narrow but solid spool of thread has radius R and mass M. If you pull up on the thread so that the CM of the spool remains suspended in the air at the same place as it unwinds, (a) what force must you exert on the thread? (B) how much work have you done by the time the...
  14. S

    Solving Rotational Motion of Wheel with 3.21 kg Block

    Homework Statement A wheel of radius 0.358 m is mounted on a frictionless horizontal axis. The rotational inertia of the wheel about the axis is 0.0421 kg·m2. A massless cord wrapped around the wheel is attached to a 3.21 kg block that slides on a horizontal frictionless surface. If a...
  15. I

    Rotational Motion of a Hanging Mass

    Homework Statement Consider a ball of mass m on the end of a string of length l. It hangs from a frictionless pivot. The ball is pulled out so that the string makes an angle thetai with the vertical and is then released. a. Find w (angular velocity) as a function of the angle the strings...
  16. P

    Rotational Motion / Torque Question

    Homework Statement A wheel has a radius of 0.40 m and is mounted on frictionless bearings. A block is suspended from a rope that is wound on the wheel and attached to it. The wheel is released from rest and the block descends 1.5 m in 2.00 s while the wheel rotates clockwise. The tension in...
  17. N

    Solving Rotational Motion: Min Force Required for Incline of 30 Degrees

    Having a problem figuring this out; it appears extremely easy but I would understand if rotational motion comes into play. I'm just not sure where. A cylinder of mass 2kg is rolled up an incline by means of a string arranged as shown in the figure. (incline with angle theta and a cylinder...
  18. S

    Minimum Velocity for Cube to Fall Off Table - Rotational Motion Question

    Solid cube of side 2a and mass M is sliding on a frictionless table with velocity v. It hits a small obstacle at the end of the table causing it to tilt. What is the minimum velocity to cause the cube to fall off the table? Totally no clue where to start I don't even know what's the condition...
  19. T

    Rubber ball Rotational Motion Question

    Note: I refrained from using any of the latex references, so bear with me. Homework Statement A rubber ball with a radius of 3.2 cm rolls along the horizontal surface of a table with a constant linear speed v. When the ball rolls off the edge of the table, it falls 0.66 m to the floor below...
  20. A

    Child on swing (rotational motion, forces) question

    Homework Statement A high school buddy exerts a horizontal force on a swing that is suspended by a rope that is 5.0 meters long, holding at an angle of 30 degrees with the vertical. The child in the swing has a mass of 30kg and dimensions that are negligible compared to the length of the...
  21. C

    Calculating Angular Speed of a Shaft with Given Angular Acceleration

    Homework Statement A shaft is turning at 73.8 rad/s at time zero. Thereafter, its angular acceleration is given by a = -10.1 rad/s2 - 4.44 t rad/s3. where t is the elapsed time. Calculate its angular speed at t = 2.58 s Homework Equations 1/2(Angular accel formula)+ 73.8t+0= theta...
  22. B

    How Long Can a Flywheel-Powered Car Run on Stored Kinetic Energy?

    Homework Statement A car is designed to get its energy from a rotating flywheel with a radius of 1.85 m and a mass of 678 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 3610 rev/min. Find the kinetic energy stored in the...
  23. B

    Rotational motion, using torque to find power

    Homework Statement An electric motor can accelerate a Ferris wheel of moment of inertia 19200kgm2 from rest to 9.11 rev/min in 10.7s. When the motor is turned off, friction causes the wheel to slow down from 9.11 rev/min to 7.36 rev/min in 9.55s. Determine the torque generated by the motor to...
  24. L

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    1. Mass m_1 on the frictionless table of the figure is connected by a string through a hole in the table to a hanging mass m_2. With what speed must m_1 rotate in a circle of radius r if m_2 is to remain hanging at rest...
  25. S

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  26. S

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  27. L

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    Homework Statement A thin rod of mass M and length L rests on a frictionless table and is struck L/4 from its CM by a clay ball of mass m moving at speed v. The ball sticks to the rod. Determine the translational and rotational motion. Homework Equations Irod=1/12*M*R^2 I=mR^2 L=Iw or L=r*m*v...
  28. T

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    ok I am not sure what this kind of motion is called but it is caused when a cylinder, a AA battery let's say, is liying on a flat smooth surface and a torque is applied to one end which causes the battery to stand up and spin on one of its ends. I've been looking for a name or a few details...
  29. S

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    Here are a couple of questions I'm having trouble with. 1) Can a magnet have 3 poles? [Note: I've been told that a magnet might develop two north poles at the centre and two south poles at either end if it is faultily magnetised, but I'd much appreciate some explanation=)] 2) If the...
  30. P

    Conceptual Rotational Motion Question

    Homework Statement Two objects of equal mass are on a turning wheel. Mass 1 is located at the rim of the wheel while mass 2 is located halfway between the rim and the axis of rotation. The wheel is rotating with a non-zero angular acceleration. For each of the following statements select the...
  31. M

    Rotational motion begining with kinetic friction.

    Homework Statement A ball is suddenly kicked across a floor. It initial will have a linear velocity, but no initial angular velocity. The object will slide for a distance "d" until perfect rolling kicks in. all are in terms of variables and not specific numbers A.) derive an equation...
  32. B

    Calculating Tire Revolutions and Angular Speed in a Braking Car

    Homework Statement A car initially traveling at 25.9 m/s undergoes a constant negative acceleration of magnitude 2.10 m/s2 after its brakes are applied. (a) How many revolutions does each tire make before the car comes to a stop, assuming the car does not skid and the tires have radii of...
  33. T

    Rotating governor (rotational motion)

    Homework Statement A rotating governator is designed as shown. A 8.66 lb collar at the bottom can slide freely along the shaft (no friction). Initially the collar is 2.00ft from the top. As the governor rotates, the collar is pulled upwards, and when it reaches a distance of 1.732 from the...
  34. D

    How Far is an Object Orbiting Earth if Its Period is 32 Days?

    Homework Statement An object of mass 7.1x1023 circles the Earth and is attracted to it with a force whose magnitude is given be Gmem/r2. If the period of rotation is 32 days, what is the distance from the Earth to the object? Here G=6.67x10-11 Nm2/kg2, me=6x1024 kg. Homework Equations...
  35. K

    Cylinder Rotational Motion Question

    A sphere of radius a rests on top of a fixed rough circular cylinder of radius R which is lying with its principal axis horizontal. The sphere is disturbed and rolls, without any slipping, around the surface of the cylinder. Show from energy considerations that, if theta is the angle to the...
  36. W

    Rotational motion and law of gravity

    Homework Statement Neutron stars are extremely dense objects that are formed from the remnants of supernova explosions. many rotate very rapidly. suppose that the mass of a certain spherical neutron star is twice the mass of the sun and its radius is 10.0 km. determine the greatest possible...
  37. E

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  38. K

    Rotational Motion: Disc Movement

    Homework Statement A 750 gram grinding wheel 25.0 cm in diameter is in the shape of a uniform solid disc. When it is in use it turns at a constant 220 rpm about an axis perpendicular to its face through its center. When the power is switched off the wheel stops in 45.0 s with constant angular...
  39. F

    Rotational motion homework question

    Homework Statement A disk with a radial line painted on it is mounted on an axle perpendicular to it and running through its center. It is initially at rest, with the line at q0 = -90°. The disk then undergoes constant angular acceleration. After accelerating for 3.1 s, the reference line has...
  40. B

    U Texas Physics Rotational Motion

    This is not a traditional homework question: Anyone familiar with the the U texas homework will understand: Does anyone have the answer key to the utexas physics homework on rotational motion? Our teacher hasn't taught us anything on rotation. We are desperate to know how to do these...
  41. K

    Rotational motion of belt drive

    Homework Statement I'm just working through a few past mechanics papers and this question came up: A belt drives the circumference of a cylindrical wheel of radius R and mass M with no slipping. The tension in the belt is T. Friction in the wheel bearing causes an effective torque N...
  42. B

    Rotational Motion Homework: Angular Momentum and Tension

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  43. N

    When Should You Launch Your Rocket to Mars?

    Homework Statement You are working on a project with NASA to launch a rocket to Mars, with the rocket blasting off from Earth when Earth and Mars are just aligned along a straight line from the sun. As a first step in doing the calculation, assume circular orbits for both planets. If Mars...
  44. I

    Rotational motion and angular displacement

    Homework Statement A baton twirler throws a spinning baton directly upward. As it goes up and returns to the twirlers hands, the baton turns through four revolutions. Ignoring air resistance and assuming that the average angular speed is 1.80 rev/s, determine the height to which the center...
  45. S

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  46. A

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  47. H

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    Homework Statement The sliding block has a mass of 0.800 kg, the counterweight has a mass of 0.460 kg, and the pulley is a hollow cylinder with a mass of 0.350 kg, an inner radius of 0.020 m, and an outer radius of 0.030 m. The coefficient of kinetic friction between the block and the...
  48. G

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  49. W

    Factor label method with rotational motion

    Suppose you are riding a stationary exercise bicycle, and the electronic meter indicates that the wheel is rotating at 8.4 rad/s. The wheel has a radius of 0.40 m. If you ride the bike for 2090 s, how far would you have gone if the bike could move? w= rad/ sec 2 pi= rev v= m/s 2pi x r=...
  50. I

    Coefficient of restitution in rotational motion

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