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

    Capa Assignment- Rotational Motion

    Hello, If anyone out there could help me with this problem it would be much appreciated. The problem is on rotational motion and it states: A proposed space station includes living quarters in a circular ring 52.0 m in diameter. At what angular speed should the ring rotate so the occupants...
  2. M

    How Can Angular Velocity Be Expressed as a Function of Theta for a Falling Rod?

    Question: "A uniform rod of mass m and length 2a stands vertically on a rough horizontal floor and is allowed to fall. Assuming that slipping has no occured, write the angular velocity of the rod as a function of the angle Theta the rod makes with the vertical." WORK DONE: Ic = (ml^2)/3...
  3. H

    Rotational Motion and Moment of Inertia Questions

    :confused: 1.) A uniform rod of mass 0.93 kg is 17 m long. The rod is pivoted about a horizontal, fric- tionless pin at the end of a thin extension (of negligible mass) a distance 17 m from the cen- ter of mass of the rod. Initially the rod makes an angle of 70 degrees with the...
  4. R

    How Does Angular Acceleration Affect Rotational Motion?

    Hey all, thought I should ask about a couple problems... 1 - A rotating door is made from four rectangular glass panes, as shown in the drawing. The mass of each pane is 95 kg. A person pushes on the outer edge of one pane with a force of F = 80 N that is directed perpendicular to the pane...
  5. J

    Some problems with rotational motion

    1) A .65 kg on the end of thin light rod is rotated in a horizontial circle of a radius 1.2 m. (a) Calculate the moment of inertia of the ball about the center of the circle, and (b) the torgue needed to keep the ball rotating at constant angular velocity if air resistence exerts a force of .020...
  6. P

    Rotational motion of a spool of wire

    A spool of thin wire rotates without friction about its axis. A man pulls down on a wire connected to an inner radius with force of 16.3 N. How long does it take to increase the angular velocity of the spool from 15.0 rad/s to 33.0 rad/s? Icm = 0.550 kgm2 Inner radius, r = 0.300 m Outer radius...
  7. S

    Rotational Motion Questions from 1st year university help

    I don't know if I'm suppose to put this in this forum because it's for 1st year university physicz..wasn't sure if it was intro or not but anyways...I need some help doing the following questions... 1.A wheel (like one of those wooden ones like they had in the oldern days) has 8 equally...
  8. K

    Rotational Motion and Equilibrium Problems, Work Checking

    I have a few Rotational Motion and Equilibrium problems that I hav been working on but I am not sure if I completed them correctly. I will show what I have done so far and if anyone could point me in the right direction I would appreciate it. Please, numerical explanations are easier for me to...
  9. W

    How Long Does It Take a Rolling Spool to Hit the Floor?

    "A string is wound around a solid cylindrical spool of mass 9.4 kg and radius .11 m. Assume the acceleration of gravity to be 9.8 m/s^2. If the spool is released from rest and rolls along the string and the distance to the floor is 9.06 meters, then how long in seconds will it take the spool...
  10. J

    Rotational Motion: Calculating Angular Speed of Disk and Neutron Star Spin Rate

    A solid cylinder, a solid sphere, and a hoop all of the same mass but different radii, roll without sliding down an inclined plane. The body that gets to the bottom first will invariably be: the cylinder the sphere they all arrive together not enough information the hoop...
  11. C

    Rotational motion -angular energy+angular acceleration

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  12. W

    Need help with a qn on rotational motion.

    A hoop pf radius r and mass m is rolling without slipping with velocity v towards a step of height h on a horizontal surface. Assume that it does not rebound and no slipping occur at the point of contact when the hoop roll up, what is the minimum velocity needed for the hoop to roll up...
  13. W

    Calculating Distance Traveled by a Point on a Rotating Wheel

    If I know a distance the center of a wheel travels and what the radius of that wheel is, in what manner can I figure out how far some point on the rim of the wheel travels?
  14. I

    How Does a Cube Exhibit Rotational Motion?

    rotational motion I have a problem with describe rotational motion for the cube, i met the rotational motion for the circle shapes but cube is somthing new, so if u know any sources, exampels or solution and book where i can find descirbe of rotational motion for cube pliss give me a sign or...
  15. D

    Rotational Motion of a Rigid Body

    hi! i've been pondering about rotational motion (of a rigid body). I've been doing some internet research on it, but i have some trouble putting things together... i want to apply forces on the particle parts of a body. one website told me that when you know the axis of rotation, you...
  16. P

    Why Does the Denominator Include mR^2 in the Angular Acceleration Formula?

    A mass (m) is connected to a pulley (rotational inertia I and radius R) which sits atop an incline with angle theta find an expression for angular acceleration in terms of M I R and theta... incline is frictionless using T= aI i get Rmgsin(theta) = aI so a...
  17. P

    Need some expertice on rotational motion

    Q) a 250kg roller coaster travels on along track as shown*** at point A and B the coaster is traveling along circular paths. the speed at point A is 20m/s what is the max speed the coaster can have at B and still remain on the track. *** ill do my best to describe this track...basically...
  18. D

    Solving Rotational Motion: Find Force on Disc Axis (4m+m)

    Can anyone help me with this question? A uniform circular disc has mass 4m and radius r. A particle of mass m is attached to the end of the disc at point A of its circumference. The loaded disc is free to rotate about a horizontal axis which is tangential to the disc at the point B, where AB...
  19. N

    Another rotational motion problem

    A spherical ball of radius r and mass m colides with a plank og mass M on a smooth horizontal surface.Before impact, the centre of the ball has a velocity vo( v knot) and angular velocity wo( omega knot) as I've shown in the figure.The norm velocity is reversed with same magnitude and the ball...
  20. N

    How Does Conservation of Momentum Affect the Motion of a Boy and a Plank on Ice?

    A boy of mass m runs on ice with velocity v and steps on the end of a plank of length l and mass M perpendicular to his path. Describe quantitatively the motion of the sytem.Neglect friction One point on the plank is at rest immediately after the collision.Where is it?
  21. J

    Speed of Tip Calc: Rotor Diam 7.6m, 450 rev/min

    have a question. diameter of a rotor is 7.60m and rotational speed of 450 rev/min. calculate speed of tip. anywell would be welcomed
  22. U

    Rotational motion - billiard ball problem

    rotational motion -- billiard ball problem I've been struggling with an AP physics free resposne problem. I have what I hope to be the right answer, but I'm not sure. Heres the question: A billiard ball has mass M, radius R, and moment of inertia about the center of mass Ic = 2/5 * M *...
  23. N

    What will happen to the rotational motion

    if a body is rotating forward towards a wall,colides with the wall ofcourse the direction of motion will be reversed,,but what will happen to the rotational motion,if it is given that the infinitely rough
  24. C

    Rotational motion about a fixed axis

    A CD has a mass of 17 g and a radius of 6.0 cm. When inserted into a player, the CD starts from rest and accelerates to an angular velocity of 20 rad/s in 0.65 s. Assuming the CD is a uniform solid disk, determine the net torque acting on it. I thought to use: torque = I * alpha...
  25. D

    Rotational Motion - Help me out GUYS

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  26. I

    How Do You Calculate Centripetal Forces on a Merry-Go-Round?

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  27. N

    Lost on rotational motion problems

    We have recently started studying rotational and rolling motion, I've struggled with this more than anything, I am pretty lost on these problems: 1) Consider a thin rod of mass 3.4 kg, length 6.8m, and uniform density. The rod is pivoted at one end on a frictionless horizontal pin. The rod...
  28. I

    Question about rotational motion and another about man on a beam

    :mad: #1. Consider the following mass distribution where the xy coordinates are given in meters: 5 kg at (0.0, 0.0) m, 3 kg at (0.0, 4.0) m, and 4 kg at (3.0, 0.0) m. Where should a fourth object of 8 kg be placed so the center of gravity of the four-object arrangement will be at (0.0, 0.0) m...
  29. P

    Calculating Rotational Motion: Proving Velocity is Perpendicular to Radius

    I calculated the equations for circlular motion as fallows... \vec{r}= p \hat{e_p} + z \hat{e_z} where e_p = unit vector in the radial direction, and so on \frac{\partial{\vec{r}}}{\partial{t}} = \dot{p}\hat{e_p} + p\dot{\theta}\hat{e_{\theta}} + \dot{z}\hat{e_z} how do i show that...
  30. V

    Simple Rotational Motion Problem

    Ok, this problem has been driving me crazy. I was thinking that the force is zero since the magnitude of the angular acceleration is zero, however that is not the case. Please help :)
  31. P

    Rectilinear and Rotational Motion

    Landing Gear of an aircraft can be modeled as a wheel with damper and spring attached horizontally. I have to show that the equation of motion is given by (I+mr^2)a + cr^2v + kr^2x = 0 where a= acceleration, v= velocity, x= displacement and spring stiffness = k and damping coefficient =...
  32. B

    Rotational Motion. Apparently, I have no idea what I'm doing.

    ok... We were given the following question... (I apologize for it's length... please bear with me) A thin long cylindrical rod (mass M radius R and length l) is initially rotating about its long axis with angular momentum L. There are no external forces or torques however interestingly Ke is...
  33. P

    Rotational Motion of a disc of mass

    I'm stuck on a miniquestion in my HW that is hindering the entire problem, so here it is. A disc of mass M, radius R, Icm =1/2MR^2 is rolling down an incline dragging a mass M attached with a light rod to a bearing at the center of the disc. The friction coefficients are the same for both...
  34. T

    Solve Rotational Motion: Show Tension = 1/3 Disk Weight

    I have a diagram for this at http://snipurl.com/diagr There is a uniform disk with radius R, mass M, it has a string wrapped around it and is attached to a fixed rod. Part 1: Show the tension in the string is 1/3 the weight of the disk what i have done for this is Torque=Fd and...
  35. D

    Calculating Arc Length for a Circling Airplane

    Hey been working on this problem for an hour. An airplane circles the airport control tower 1.0 times while 4.5 km away. Calculate the length of arc through which the plane travels. The only formula i can think of that remotely resembles something to be use on this is F=mv^2/r please...
  36. S

    Equilibrium and Rotational Motion

    Two identical signs, each of mass M, are held aloft in adjacent archways. Following wind, several ropes holding the sign snap, leaving only those below. If each sign is in translational equilibrium, find the tensions of the remaining ropes in terms of its mass and gravity g. Pics...
  37. S

    Rotational Motion: Speed of 13kg Cylinder on 30° & 60° Inclines

    A 13 kg cylinder with a .54 m diameter rolls without slipping down a 30 degree incline from a height of 1.25 m. a. If the cylinder has I = (mr^2)/2, what will its speed be at the incline's base? After using the conservation of mechanical energy I got v = sqrt[(4/3)gh], which is 4.04 m/s...
  38. V

    Free falling rotational motion

    There is a post with length L and it is being cut down from its lowest point. So the post starts a free fall with circular trajector. The question is that what is the v of upper part of post when it hits the ground? I used energetic method and mvL= 0,5mv^2 plus or minus something... i have a...
  39. S

    Flywheels and Rotational Motion

    One possibility for a low-pollution automobile is for it to use energy stored in a heavy rotating flywheel of mass 240 kg, and should be able to travel 300 km (300,000 m) without needing a flywheel "spinup." Make reasonable assumptions (avg. frictional retarding force 500 N, 20 acceleration...
  40. S

    Bicycles and Rotational Motion

    How is the angular speed of the rear wheel (w_R) of a bicycle related to that of the pedals and front sprocket (w_F) ? To show this relationship, I have to derive a formula for w_R/w_F. N_F and N_R are the number of teeth on the front and rear sprockets , respectively. The teeth are spaced...
  41. P

    Solving Rotational Motion: Coin Rolling Up Inclined Plane

    I'm having a problem with the following question: A coin with radius R rolls up a plane which is inclined at an 25 degrees above the horizontal. The coin starts up the incline with an initial angular velocity of 70 rad/s and rolls in a straight line without slipping. How far will the coin...
  42. J

    Calculating Linear Acceleration on a Rotating Record

    Q: What is the linear acceleration of a point on the rim of a 30-cm-diameter record rotating at a constant angular speed of 33.5 rev/min? I seem to have all the variables and equations in hand - r = .15m and \omega = 3.49 radians/second; v = \omega r ; (radial component of linear...
  43. J

    Rotational Motion: Who Reaches Bottom First?

    Two hoops of identical radii roll without slipping down identical inclined planes under the influence of gravity. Hoop 1 is identical to Hoop 2 except for some massive spokes which are fixed to the rim. If the two hoops are released at the same time from the same height, which hoop makes it...
  44. P

    Rotational Motion Questions -

    I have been stuck on these forever...but here goes: 1st question: A tire placed on a balancing machine in a service station starts from rest and turns through 5.5 revs in 1.0 s before reaching its final angular speed. Assuming that the angular acceleration of the wheel is constant...
  45. B

    Rotational Motion About a Fixed Axis

    Hello again. I thought I had this problem figured out but once again, I did not. Here's the problem: A solid circular disk has a mass of 1.2kg and a radius of 0.12m. Each of three identical thin rods has a mass of 0.12kg. The rods are attached perpendicularly to the plane of the disk at...
  46. S

    Rotational Motion of a long pole

    A 3.3m long pole is balanced vertically on its tip. It is given a tiny push. What will be the speed of the upper end of the pole just before it hits the ground? Assume the lower end does not slip. mgh=.5mv^2 + .5Iw^2 Initial PE = final KE translation + final KE rotational v=rw, I=.33mr^2...
  47. BobG

    Kinetic Energy due to rotational motion

    The kinetic energy of a body due to rotational motion is a scalar using the following equation: E=\frac{1}{2}I\omega^2 Except, the moment of inertia is nomally expressed as a matrix and the angular velocity as a vector, as in the equation for angular momentum: \vec{H}=[I]\vec{\omega}...
  48. S

    Rotational Motion FInding the total ENergy

    Particulars: ball has a radius of 2.5 cm a mass of .125 and is rolling across a table with a speed of .547 m/s, this table is 1.04 m off the ground. It rolls to the edge and down a ramp How fast will it be rolling across the floor? First I found the Gravitational Potential Energy: Ep=mgh...
  49. E

    Solving a Rotational Motion Problem: Determining Angular Velocity & Speed

    Hello, I need to confirm my solution to this problem: A thin rod of length l stands vertically on a table. The rod begins to fall, but its lower end does not slide. (a) Determine the angular velocity of the rod as a function of the angle \phi it makes with the tabletop. (b) What is the speed...
  50. R

    Rotational motion of a car's tires

    A car accelerates uniformly from rest and reaches a speed of 19.0 m/s in 7.00 s. The diameter of a tire is 64.0 cm. (a) Find the number of revolutions the tire makes during this motion, assuming no slipping. (b) What is the final rotational speed of a tire in revolutions per second...
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