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. J

    Rotational Inertia: Calculate & Plot Function w/ Sinus Decay

    Hi, I would like to calculate the function of a rotating disc that has 2 spring slowing it down. (look at my pictures to understand) Let say I turn my disc 90 degrees clockwise and release it, it is going to oscillate a certain moment than stop. I want to plot that function and to have a...
  2. L

    Calculating Rotational Inertia (A Bit of Confusion)

    Hey all, Perhaps this is a bit stupid... I'm familiar with the normal procedure of calculating rotational inertia (using integration, parallel axis theorem, etc.). However, I had a confusing thought: if the center of mass of a body is the point at which you can treat as all of the mass being...
  3. S

    How Much Energy is Stored in a Hurricane's Rotation?

    Rotational Motion Question -- please help Homework Statement Estimate the energy stored in the rotational motion of a hurricane. Model the hurricane as a uniform cylinder 300 km and 5 km high, made of air whose mass is 1.3 kg/m^3. Estimate the outer edge of the hurricane to move at a speed...
  4. I

    Rotational Physics: Stopping a Wheel in .3 sec

    Homework Statement A kid turns his bike upside down and spins the tire at 2 revolutions per second. The spoked wheel measures 26 inches in diameter and weighs 5 lbs. The kid presses a piece of metal against the rubber tire to bring it to a halt. About how long will it take to bring the wheel...
  5. P

    Finding the angular velocity and rotational kinetic energy

    Homework Statement A solid cylinder is rolling along a horizontal plane and is friction less around its symmetric axis. The cylinder is pulled by a constant force, F and travels the distance, d. The cylinder does not glide and has a friction force, f on the ground. Known values: Mass: M...
  6. W

    How to Calculate Time and Angular Acceleration of a Slowing Disc

    The mass of the disc is M and the radius is R. The problem states: A disc completes 44 revolutions as it slows from an angular speed of 1.5 rad/sec to a complete stop. 1)W/ acceleration constant, what times is required for it to come to rest? 2) what is the angular acceleration...
  7. P

    Rotational and Translational Forces

    I am having a hard time proving this to myself: Given some object with a known inertial moment and center of mass, with r = distance from COM, do forces of equal magnitude along some line L perpendicular to R all yield the same F_t (translational force) and F_r(rotational force), and how can...
  8. NATURE.M

    Linear acceleration and rotational motion

    Homework Statement You are the technical consultant for an action-adventure film in which a stunt calls for the hero to drop off a 20.0-m-tall building and land on the ground safely at a final vertical speed of 4.00 m/s. At the edge of the building’s roof, there is a 100-kg drum that is...
  9. G

    Rotational Kinetic Energy: Pole Balanced Vertically

    Homework Statement A 1.80m long pole is balanced vertically with its tip on the ground. It starts to fall and its lower end does not slip. What will be the speed of the upper end of the pole just before it hits the ground? [hint: Use conservation of energy] l=1.890m Homework...
  10. A

    Frictional force (static) = 6 NSolved: Rotational Mechanics Homework

    Homework Statement A plank having mass 3.7 kg rides on top of two identical solid cylindrical rollers each having radius 5.5 cm and mass 2.9 kg. The plank is pulled by a constant horizontal force of 6 N applied to its end and perpendicular to the axes of the cylinders(which are parallel)...
  11. E

    How does rotational kinetic energy increase in rolling downhill?

    Homework Statement This is not a homework problem. Okay, it is -- but I have solved it correctly already, so the question is not there. I'm just not sure about a detail in one of many solutions. We have a hollow cylinder with a uniform mass distribution rolling down an incline with some...
  12. Q

    Planet and Car rotational movement

    Homework Statement A newly discovered planet has a mean radius of 1230 km. A vehicle on the planet's surface is moving in the same direction as the planet's rotation, and its speedometer reads 130 km/h. If the angular velocity of the vehicle about the planet's center is 6.18 times as large...
  13. J

    What fraction of its total kinetic energy is rotational kinetic energy

    Homework Statement A spherical object with moment of inertia 0.57mr2 rolls without slipping down an incline. At the bottom of the incline. Homework Equations For a sphere (or cylinder) rolling without slipping ω = v/r. Rotational KE = ½Iω² The translational kinetic energy = ½mv²...
  14. NATURE.M

    Rotational motion: Expression for Angular Velocity

    Homework Statement A solid flywheel of radius R and mass M is mounted on a light shaft of radius r so that the axis of rotation is horizontal. A light, inelastic rope is wound around the drive shaft and is connected, via a light, frictionless pulley to a mass m, which is suspended a height h...
  15. A

    Rotational Mechanics: Plank Acceleration and Frictional Force Calculation

    Homework Statement A plank having mass 3.7 kg rides on top of two identical solid cylindrical rollers each having radius 5.5 cm and mass 2.9 kg. The plank is pulled by a constant horizontal force of 6 N applied to its end and perpendicular to the axes of the cylinders(which are parallel)...
  16. N

    Rotational Kinematics - Angular Acceleration

    Homework Statement A phonograph turntable with an initial angular velocity of 78 rpm continues turning for 40 rotations after being switched off. What is the angular deceleration of the turntable? Assume constant angular deceleration. Homework Equations \alpha=(\omega-\omega0)/t...
  17. H

    Help with rotational motion work

    Homework Statement A billiards ball of mass M is initially motionless on a table when it is hit by a cue projecting it forward with speed V and no angular velocity. Find the speed of the ball when it eventually begins to roll. Assume the ball does not slip when it begins to roll. What...
  18. N

    Rotational Motion Conceptual Question

    Homework Statement A spool of wire rests on a horizontal surface as in Figure P10.87. As the wire is pulled, the spool does not slip at the contact point P. On separate trials, each one of the forces F1, F2, F3, and F4 is applied to the spool. For each one of these forces, determine the...
  19. P

    How is torque calculated for rotational motion involving a winch system?

    1. Homework Statement This question is about forces and rotational motion. (a) Figure 1.1 illustrates a force of 180 N acting at a perpendicular distance of 0.40 m from a point O. Calculate the torque about O. (b) Figure 1.2 illustrates a circular drum of radius 0.080 m around which a...
  20. B

    Question regarding rotational measurements

    Hi, This isn't my field at all so please excuse my ignorance. Let's say I have a pipe positioned at 30 degrees to the horizontal and an inclinometer attached to the pipe in a vertical position. Now I rotate the pipe some amount about it's long axis. The inclinometer reads 15 (or...
  21. M

    What Determines the Minimum Height for a Marble to Complete a Loop-the-Loop?

    A solid marble starts from rest and rolls without slipping on the loop-the-loop track in Fig. 10.30. Find the minimum starting height from which the marble will remain on the track through the loop. Assume the marble’s radius is small compared with R. Solution: In the question, why is the...
  22. M

    Calculate Rotational Energy of Ship's Anchor: 5000 N Weight

    60. A ship’s anchor weighs 5000 N. Its cable passes over a roller of negligible mass and is wound around a hollow cylindrical drum of mass 380 kg and radius 1.1 m, mounted on a frictionless axle. The anchor is released and drops 16 m to the water. Use energy considerations to determine the...
  23. M

    Interpreting force in rotational motion

    56. A motor is connected to a solid cylindrical drum with diameter 1.2 m and mass 51 kg. A massless rope is attached to the drum and tied at the other end to a 38-kg weight, so the rope will wind onto the drum as it turns. What torque must the motor apply if the weight is to be lifted with...
  24. L

    K of Rotation vs Rotational Momentum

    Homework Statement A space station has the form of a hoop of radius R = 15 m, with mass M = 1000 kg. Initially its center of mass is not moving, but it is spinning with angular speed ωi = 4 rad/s. A small package of mass m = 22 kg is thrown at high velocity by a spring-loaded gun at an angle θ...
  25. R

    Rotational Kinetic Energy of Planet

    Homework Statement This question has two parts; the first part I understand but the second part I do not. Part 1: What is the rotational energy of a planet about its spin axis? Model the planet as a uniform sphere of radius 6420 km, and mass 5.59x10^24 kg. Assume it has a rotational period...
  26. A

    Rotational Energy and Linear Momentum Problem

    Homework Statement In the figure here, a small, solid, uniform ball is to be shot from point P so that it rolls smoothly along a horizontal path, up along a ramp, and onto a plateau. Then it leaves the plateau horizontally to land on a game board, at a horizontal distance d from the right edge...
  27. A

    Rotational Dynamics: Analyzing Frictional Force Direction

    When I am browsing through my rotational dynamics chapter, I raise myself a question on the direction of frictional force under all kinds of possible circumstances: 1. Pure rolling For pure rolling, the frictional force will always be 0; 2. Non-pure rolling For this situation, I...
  28. Glenstr

    Layperson's question regarding earth's rotational wobble

    Our carpool conversation this time of year usually involves the shortening daylight hours, which are quite noticeable given that we are between the 54th and 55th parallel. After each new year arrives we start watching the horizon as we're leaving work (at 5pm) waiting for the day when we start...
  29. P

    What is the Kinetic Energy of a Rotating Square Mass-Spring System?

    Homework Statement Four masses M in deep space are connected by four identical light springs with spring constant k and equilibrium length L. The four mass, four spring assembly is square and lies in a plane; all four masses are rotating with ω =√(k/M), in uniform circular motion about an axis...
  30. hb20007

    Rotational Kinematics: Slowing Down Turntable

    Homework Statement A turntable is a uniform disc of mass m and radius R. The turntable is initially spinning clockwise when looked down on from above at a constant frequency f_0. The motor is turned off at t=0 and the turntable slows to a stop in time t with constant angular deceleration...
  31. P

    Rotational mechanical systems and electrical analogs.

    Hi, Homework Statement Upon converting rotational mechanical components into their electrical analogs, one thing in particular baffles me. When is a rotational component converted into two sets of dependent sources and when is it converted into a single set? Let me try and clarify my question...
  32. J

    Rotational Torque, Forces, Tipping

    Homework Statement A refrigerator has a vertical center of mass .5m above the floor, and a horizontal center of mass of .5m which is in the horizontal center, the mass of the fridge is 200kg. What is the maximum initial horizontal force a machine can apply to the fridge which is at rest for...
  33. Crusader711

    Translational and rotational kinetic energy-Mass Unknown

    A hollow, thin-walled sphere (ICM = 2MR2/3) of mass 20 kg is completely filled with a liquid of unknown mass. The sphere is released at the top of a plane inclined at 30° to the horizontal, and it rolls 20 m to the bottom in 3.6 s. What is the mass of the liquid? 2.My approach is...
  34. PhysicsKid0123

    Sphere vs Cube: Rotational Inertia

    Which would have more rotational inertia? A sphere or cube? Suppose they have the same mass, the side of the cube has the same length as the diameter of the sphere, the cube's rotation axis is perpendicular to two of its faces. Which one would have more rotational inertia about an axis through...
  35. N

    Rotational Dynamics of two disks

    Homework Statement Two disks are spinning freely about axes that run through their respective centres (see figure below). The larger disk (R1 = 1.42 m) has a moment of inertia of 1070 kg · m2 and an angular speed of 4.2 rad/s. The smaller disk (R2 = 0.60 m) has a moment of inertia of...
  36. K

    MHB Decomposition formulas for rotational symmetries of a cube

    I have a problem that I would like to check my work on. I am also stuck on the verifications for $E$ and $F$. Any help would be greatly appreciated. Thanks in advance. **Problem statement:** Let $G$ be the group of rotational symmetries of a cube, let $G_v, G_e, G_f$ be the stabilizers of a...
  37. T

    Rotational Kinematics of two masses

    Homework Statement Consider a system of two masses joined by a massless string with the string passing over a massless frictionless pulley with a radius of 5.0 cm. The mass of the left is 9.00 kg and the mass on the right is 1.60 kg. Find the angular acceleration of the pulley when the...
  38. L

    Angular Momentum and Rotational Energy

    Homework Statement Figure: http://i.imgur.com/E2D1hkW.png A massless rod of length 2R is attached at the middle to a pivot point that allows it to rotate in the vertical plane. Masses m and 2m are attached to the rod at the locations depicted in the figure. Initially the rod makes an angle of...
  39. K

    MHB Orders of elements for rotational symmetries of cube

    I am having lots of trouble doing this problem because I have particularly poor visualization skills. (Or maybe haven't developed them well yet). I would appreciate any help on this math problem. Here is the question: Suppose a cube is oriented before you so that from your point of view there...
  40. E

    Rotational Kinetic Energy and Frictionless Surfaces

    What happens if a ball goes from rolling on a surface to a frictionless surface? I know friction is required for the ball to roll, so would the rotational energy be transformed into translational energy (the ball goes faster without rolling), or does something else happen? Thanks!
  41. W

    Linear and Rotational Kinetic Energy

    Homework Statement A solid cylinder is rolling without slipping. What fraction of its kinetic energy is linear? Homework Equations Ke=\frac{mv^2}{2}+\frac{I(v/r)^2}{2} The Attempt at a SolutionKe=\frac{mv^2}{2}+\frac{(v/r)^2}{2}*\frac{(mr)^2}{2} Ke=\frac{3(mv)^2}{4} Linear Ke...
  42. X

    Understanding Rotational Inertia: A Homework Challenge

    Homework Statement in Attachment Homework Equations I = .5*mr^2 The Attempt at a Solution I have no idea what is going on. This is a pre section quiz and I guessed on one and got it right. I don't know what is meant by the equations not giving I. I googled and noticed I has...
  43. R

    Effect of Rotational Direction on a Football.

    While learning about angular momentum in class my professor posed the question, "Why are their less left handed quarterbacks in the NFL than right handed?". He goes on to explain that in the case of a right handed quarterback the ball is given a clockwise rotation giving it angular momentum in...
  44. T

    Rotational motion of rear wheels

    A 1500 kg car is driven onto a pair of ramps so that it fronts wheels have been raised 0.3 m above the rear wheels. The wheel base of the car is 2.4m and it center of gravity is located at the midpoint between the front and rear wheels. How much of the car's weight is supported by the rear...
  45. A

    Rotational Spectroscopy Question

    Which of the following molecules can be studied by purely rotational spectroscopy? a) NH3 b) N2 c) CH4 d) SF6 e) CS f) CS2 The attempt at a solution[/b] To my understanding, using only rotational spectroscopy could be used to study b) N2 and e) CS but I am not sure about my answer...
  46. W

    Circular Motion Rotational Axis

    Homework Statement Child P happens to be at a greater distance from the rotation axis than Child M. Which child has the greatest angular velocity? 2. The attempt at a solution Do they have the same angular velocity, and if they do can you please explain. Thank you.
  47. L

    Problem with rotational torque and angular acceleration

    I've attached a screenshot of this particular question. I was able to figure out part A but I'm having some difficulty with part B. Relevant equations: T = I*alpha I = .5mr^2 (for a solid cylinder like the grinding wheel) F = ma Attempt at solution: I've gotten as far as setting up...
  48. U

    Torque, rotational inertia and angular acceleartion

    Homework Statement In order to link these into a logical sequence, how do they fit together Homework Equations I = rotational inertia a = angular acceleration (I know a different symbol is usually used) τ= force x moment arm distance The Attempt at a Solution so...to...
  49. 0

    Work–kinetic energy theorem for rotational motion. need to be symetri?

    Why it need to be symetric From the book Physics - Serway Thanks Edit: I'm bringing just the statement from Serway's Physics 9th p 313
  50. N

    A simple rotational motion question

    Homework Statement A solid cylinder of mass M =1kg and radius 0.5m is pivoted at its centre and has three particles of mass m=0.1 mounted at its perimeter on the curved surface.The system is initially at rest.Find the angular speed of the cylinder,when it is swung through 900 in anticlockwise...
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