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. E

    Hula Hoop Rotational Motion Problem

    Homework Statement In throwing a hulahoop with back spin, you toss the hoop to the right, and it (1) moves right with speed v0, but rotates ccw with speed ω0. At some point, O, (2) it will change direction, and at that point it will start moving to the, left, but still be sliding because it...
  2. C

    Dynamics of Rotational Motion: Quarry Crane Problem

    Homework Statement A quarry crane is used to lift massive rocks from a quarry pit. Consider the simplified model of such a crane shown in the figure. (Figure 1) The ends of two poles are anchored to the ground at the same point (point O). From this point, one pole rises vertically and the...
  3. B

    Solving a Rotational Motion Problem: Finding Acceleration of Two Blocks

    Hey guys, So, I'm kinda distraught over this problem because, by all accounts, I should be able to get the problem no sweat. However, it just hasn't been happening. If you could point out my flaw, I would truly appreciate it! In the problem, we are asked to find the magnitude of the...
  4. J

    Understanding Rotational Motion: Solving for Linear and Angular Acceleration

    Homework Statement Consider a sphere that is placed at a table. The coefficient of kinetic friction between the sphere and the table is μ. At time t = 0, the velocity of the center of mass of the sphere is Vo = 0, and the sphere is rotating with respect of the horizontal axis with angular...
  5. K

    Rotational motion inelastic collision

    Homework Statement A ball of clay of mass m travels with velocity v in a path tangent to a disk of radius R and mass M. The clay collides with the disk tangentially to its outer rim ( a totally inelastic collision) and the clay and disk begins to spin about the axis. a) What is the final...
  6. V

    Rotational motion problem, half solved, can't figure out other half.

    Edit: Nevermind, solved it. Homework Statement A ceiling fan with 80 cm-diameter blades is turning at 60rpm . Suppose the fan coasts to a stop 25 s after being turned off. What is the speed of the tip of the blade 10 seconds after being turned off? Through how many revolutions does the fan...
  7. L

    Mastering Physics: Rotational Motion Around Two Cylinders

    Homework Statement The ropes in the figure are each wrapped around a cylinder, and the two cylinders are fastened together. The smaller cylinder has a diameter of 10 cm and a mass of 5.0 kg; the larger cylinder has a diameter of 20 cm and a mass of 20 kg. What is the angular acceleration of...
  8. L

    Rotational Motion Around Two Cylinders

    Homework Statement The ropes in the figure are each wrapped around a cylinder, and the two cylinders are fastened together. The smaller cylinder has a diameter of 10 cm and a mass of 5.0 kg; the larger cylinder has a diameter of 20 cm and a mass of 20 kg. What is the angular acceleration of...
  9. D

    Friction force in rotational motion

    My textbook says, "for an object rolling without slipping down an incline, the frictional force fs is less than or equal to its maximum value. fs < μsFn Why is that? What happen it's greater than?? When do we have static friction in rotational motion? (for rolling object) Then in an example...
  10. E

    Question in rotational motion

    Homework Statement A vacuum cleaner belt is looped over a shaft of radius 0.45 cm and a wheel of radius 1.80 cm. The arrangement of the belt, shaft, and wheel is similar to that of the chain and sprockets in Fig. Q9.4. (Just like a bicycle).The motor turns the shaft at 60 rev/s, and the...
  11. E

    Rotational Motion: The Relationship Between Linear and Angular Displacement

    Suppose a mass attached to a rope which winds around a rim or a disk. If the mass attached to the string falls x meters, should the string also move thorugh x meters around the rim or the disk which we can relate by s = r theta?
  12. E

    Question in rotational motion

    In rotational motion what is the difference between angular acceleration, radial acceleration and tangential acceleration?? ... Now suppose a rotating disk about its center (axis) rotating and a mass attached to the string of the rotating disk. By what v does it move... Is it just like v-rW...
  13. K

    Conservation of linear momentum and rotational motion

    When you open a door you apply force in any particular direction and as a result you get rotational motion of the door. My question is how linear momentum is conserved in this case as linear momentum seems to have generated rotational motion? To clarify my question further, if we fix a rod from...
  14. B

    Why is torque perpendicular to the plane of rotation in rotational motion?

    Hello, Of the different rotational quantities of motion--angular velocity, angular acceleration, torque, angular momentum, etc.--, which of them has their direction perpendicular to the plane of rotation (not sure if I worded that correctly)? I am pretty certain that torque has its...
  15. C

    Normal force in rotational motion

    Hi there, I've got a conceptual question about the normal force as applied to rotational motion. Suppose you have an object like a uniform disk. If the disk were set up so that its axis of rotation were about its centre of mass, it would just sit there and the normal force would be equal to...
  16. S

    Rotational Motion: Energy Conservation

    Homework Statement the sliding block has a mass of .850kg the counterweight has a mass of .420kg , and the pulley has a mass of .350kg with outer and inner radius .030m, .020m, the coefficient of friction is .250. the pulley turns the axle. the light cord does not stretch and does not slip on...
  17. G

    Using Newtons 2nd law for rotational motion

    I've attached an image explaining the problem. All pulleys are massless. Basically, they want me to show some relations between wire tensions, using Newtons 2nd law for rotational motion. This law is written in my book as: dL / dt = torque, where L is angular momentum. I'm not sure...
  18. T

    Conservation of energy with springs and rotational motion

    Homework Statement Homework Equations T1 + V1 = T2 + V2 T = kinetic energy V = potential energy The Attempt at a Solution I am only confused about how to get T2. Here is how the answer key gets T2: I don't get why Va = Vb = 0. The wheels have some velocity so it doesn't...
  19. T

    Conservation of energy with rotational motion problem

    Homework Statement Alright so I am confused about why the solution does not include the kinetic energy due to rotational energy from I_g2 as indicated in red in the following image. I don't understand why they would neglect it... I calculated the value and it makes a big difference.
  20. W

    Rotational Motion of Masses Problem

    Homework Statement Hey all - I'm doing a physics lab on rotational motion, and I can not make sense of the last part, the additional analysis. The question is: Since our masses are not actually point-masses, the theoretical model I = MR^2 is not very accurate, so for a better theoretical...
  21. I

    Which components of the force create Rotational motion?

    Which components of the force create Rotational motion?
  22. V

    How Do You Calculate Average Angular Acceleration?

    Homework Statement A rolling wheel moving to the right initially has an angular speed of 7.0 rad/s but after making 3 complete revolutions the wheel has a final angular speed of 11.0 rad/s. What is the magnitude and direction of the average angular acceleration of the wheel? Homework...
  23. M

    Rotational Motion Problem Help

    A solid, uniform disk of radius 0.250 m and mass 57.7 kg rolls down a ramp of length 3.70 m that makes an angle of 14° with the horizontal. The disk starts from rest from the top of the ramp. (a) Find the speed of the disk's center of mass when it reaches the bottom of the ramp. (b) Find the...
  24. J

    Rotational motion pendulum problem

    Homework Statement Homework Equations ƩF = ma The Attempt at a Solution I know how to break this problem up into the x and y direction Y Direction: Ft cosθ - Fg = 0 X Direction: Ft sinθ - Fg = mv2 / r The hint says to find the inward radial component. I'm guessing this...
  25. J

    Rotational motion roller coaster problem

    Homework Statement Homework Equations ƩF = ma = (mv2) / r The Attempt at a Solution For part A: Fn - Fg = (mv2) / r Fn = ((mv2) / r ) + mg Fn = (500x20^2) / 10 + 500x9.8 Fn = 24900 This seems too high to be true. But I'm unsure of what I did wrong. I know the normal force...
  26. C

    Rotational Motion to Linear Motion

    This is a question for a rather odd purpose. I came across a working LEGO model of a Russian tank and I'm trying to model it using CAD software. It has a motorized system to elevate and lower the main cannon. This is where putting it into words might get weird: It uses a small motor which...
  27. F

    Work Energy Method for Rotational Motion

    Homework Statement I don't how how to work out for the Gravitational Energy "H". Info given is 1.5rev converting to 9.42rad/s S=rδ S=0.2x9.42 =1.884 *Should i multiply the axle radius or wheel? The Attempt at a Solution E1=K1+G1+S1 =1/2(8.5)202+(20)(9.81)(H)+0Thanks
  28. F

    Work Energy Method for Rotational Motion

    Homework Statement Reference to part C of the question, I would like to ask for work done U1to2, how come linear motion is not included? I thought both linear and rotational exist since the parcel "move downwards" (linear) and the wheel is rotating (rotational) Thanks...
  29. F

    Work Energy Method for Rotational Motion

    Homework Statement Hi guys, I would like to ask for this particular question, The GPE is 0 for all position is because I set datum as the original position, GPE = 0 and when the string got detached from the axle, there is no GPE for datum 2. Am I right? Thanks
  30. Saitama

    Solving Rotational Motion Homework: a2 = 5m/s^2

    Homework Statement http://i46.tinypic.com/548uox.pngHomework Equations The Attempt at a Solution My teacher said that we will take the axis at the point which is in contact with the ground (i don't get why we need to do so?). I followed the teacher's hint. Angular acceleration α=a/R, where a is...
  31. Saitama

    Rotational Motion Homework: Find Kinetic Energy of Rod

    Homework Statement A thin rod of length L and mass m is suspended freely from one end. It is pulled to one side and then allowed to swing like a pendulum, passing through its lowest position with angular speed ω. In terms of these symbols and g, and neglecting friction and air resistance, find...
  32. N

    Calc Centripetal Acceleration: Rotational Motion & Vinyl Record Player

    In the days before compact discs and MP3 players (ancient history!), music was recorded in scratches in the surface of vinyl-coated disks called records. In a typical record player, the record rotated with a period of 3.6 s. Find the centripetal acceleration of a point on the edge of the record...
  33. N

    Rotational Motion and speed of a disc

    A 36.5-cm diameter disk rotates with a constant angular acceleration of 2.00 rad/s2. It starts from rest at t = 0, and a line drawn from the center of the disk to a point P on the rim of the disk makes an angle of 57.3° with the positive x-axis at this time. (a) Find the angular speed of the...
  34. K

    Calculating Linear and Rotational Motion

    Homework Statement In this given pole, mass is "M" and length is "L" and it is on a frictionless surface as the picture describes. "G" is the center of gravity and "I" is the inertia. A ball with a mass of "m" comes as the picture and hits the pole with a velocity of "v" and turns the...
  35. E

    Rotational Motion- Parallel Axis Theorem?

    Homework Statement A meter stick is held to a wall by a nail passing through the 60-cm mark. The meter stick is free to swing about this nail, without friction. If the meter stick is released from an initial horizontal position, what angular velocity will it attain when it swings through the...
  36. F

    Troubleshooting Tension: A Closer Look at Rotational Motion Calculations

    Homework Statement The tension answer I got is different from the answer. Can someone help me take a look at my working? Really appreciate your time in doing this. Thanks alot.
  37. J

    Rotational Motion, angular velocity

    Homework Statement Two people are on a ride where the inside cars rotate at constant angular velocity three times the constant angular velocity of the outer cars. If the two cars are in line at t = 0, and moving at 3ω and ω respectively, at what time will they next pass each other? The...
  38. F

    Kinematics of Rotational Motion Part II

    Homework Statement I cannot get the answer for part c, -13.02rad/s^2 The Attempt at a Solution 52.08=260.42+α(10) -208.34=10α α= -20.83rad/s^2 (Correct) 0=52.08+α(10) -52.08=10α α=-5.208rad/s^2 (Wrong) Please help, thanks..
  39. F

    Kinematics of Rotational Motion (Gears)

    Homework Statement Since Gear A -------- Vi=0 t=12s θ=40∏ as given in the question, can I assume that Vi=0 t=12s for Gear B/Drum C as well? If not why? Thanks..
  40. T

    The Physics of Fishing and Rotational Motion

    Homework Statement I am writing a large paper on the physics of fishing and would like to know what equation would prove the statement that a longer fishing pole would result in a higher velocity of the lure? My physics book gives me a gamut of equations for rotational motion but I can't...
  41. azizlwl

    Rotational motion, frictionless.

    http://img444.imageshack.us/img444/8148/rollwx.jpg A rope is wound around a cylinder of mass 4kg, and I=0.02kg.m2 about the cylinder axis. The frictional force between table and cylinder is negligible. Solution: a=20/4=5.0m/s2 α=ar is not applicable when slippage occurs. My...
  42. T

    Rotational Motion and Coefficient of Friction

    Hey guys! Ok, so I don't have that much to work with, and I am sorry for my lack of detail, but my memory is a bit fuzzy. I had to do a problem like this for my physics test yesturday: On the test we were given a problem involving a roller coaster (Rotating Drum of Death was its name)...
  43. F

    Solve Rotational Motion Homework: Pulleys A, B, C

    Homework Statement Attached 1st pic is the question, 2nd pic is the formula PS: I am sorry if i have posted on the wrong section. The Attempt at a Solution My understanding for this question is for compound pulley, angular velocity is the same, linear velocity is different. For pulleys in...
  44. F

    Solving Doubts on Rotational Motion

    Hi guys, I have a few doubts on Rotational Motion and hope someone can help me out. This 3 formula is for finding angular velocity, angular acceleration and angular displacement right? ω=ωi+αt ω²=ωi²+2αδ δ=ωit+1/2αt² And this 3 formula is for finding the linear...
  45. N

    Rotational motion of a spinning disk

    Homework Statement A spinning disk is rotating at a rate of 30 rad/s in the counterclockwise direction. The disk is slowing down at a rate of 6 rad/s2. Find the angle through which the disk has turned after 3 s in radians, degrees, and revolutions. Homework Equations θ=θi + ωi*t + αt^2...
  46. Y

    Mastering Physics 10.85 - Dynamics of Rotational Motion

    This is my first post on here; I hope it will be worth it. I haven't been able to find an adequate solution to this elsewhere. Homework Statement A 5.30 kg ball is dropped from a height of 11.5 m above one end of a uniform bar that pivots at its center. The bar has mass 8.50 kg and is 9.00 m...
  47. Z

    What is the angular acceleration of a falling rod with two attached balls?

    Homework Statement A thin, uniform 3.60kg bar has two balls glued on either end, each with a weight of 2.5kg. The length of the rod is 90cm and is balanced in the center. When one ball falls off calculate the angular acceleration just after this happens. (e.g the rod is falling in a...
  48. D

    Circular rotational motion (kinematics)

    Homework Statement A wheel starts from rest and accelerates uniformly to 200rpm in 6s. After it has been rotating for some time at this speed, the brakes are applied and it takes 5 minutes to stop the wheel. If the total number of revolutions is 3100, calculate the total time of rotation...
  49. B

    Analyzing Rotational Motion of Massless Rod and Object

    Homework Statement A mass-less rod of length, Ls, is rotating clockwise about a point, P1 in the horizontal plane. Attached by a cable of length, Ls, to the end of the rod and at angle θ is an object of mass, M. Starting at rest and then with the rod having and angular acceleration α, describe...
  50. E

    Rotational motion and moment of inertia-HELP

    rotational motion and moment of inertia---HELP! Homework Statement Two masses m1=2.00 kg and m2=1.00 kg are linked by a thread and thrown over a pulley whose mass is 1.00 kg. The radius of the pulley is 0.200 m. a) Find the acceleration a with which the weights move b) the tensions T1...
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