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. P

    Rotational exited states spin and parity

    Hi, If you have a even-even nuclei which is deformed, you get a rotational spectrum of 0+,2+,4+,... I don't understand why the parities are positive for even I and why all members of a rotational band must have the same parity. I read about this in Krane's book: an introduction to nuclear...
  2. H

    Barrel cam design, Torsion, Rotational Speed, Displacement

    Hello I'm a student and I have project making a harvesting tool which need barrel cam I need force to cut trunk of coconut tree (I don't know it in english, what I mean is the hard part of coconut leaf) I'm a bit confuse here from Robert L Norton book Cam Design and Manufacturing...
  3. V

    Rotational speed at axis of rotation?

    Hello everyone! This is probably the stupidest question that I've come up with, and I'm a little embarrassed asking it, but here goes: Is it only the tangential speed that is zero of a point at the axis of rotation in a rotating solid? If not, then I don't understand how the rotational...
  4. J

    Variable MOI: Rotational 2nd Law

    I'm having trouble finding any sources that discuss equations of motion that take into account a changing moment of inertia. Just looking at the scaler case, angular momentum is L = I\omega Then, according to the 2nd law, \tau = \frac{d}{dt}(L) = \dot{I}\omega + I\alpha Is this correct...
  5. T

    Can Rotational Dynamics be derived from Translational Dynamics?

    Torque, in particular, is always a concept that has confused me. Can the rules related to torque be derived or are they natural tendencies? (For lack of a better way to phrase this). For example, if I were trying to solve the problem of a ladder leaning against a frictionless wall, where I...
  6. PsychonautQQ

    Rotational Motion / Torque problem (what did i do wrong?)

    Homework Statement A thin, light wire is wrapped around the rim of a wheel,. The wheel rotates without friction about a stationary horizontal axis that passes through the center of the wheel. The wheel is a uniform disk with radius R = .280m. An object of mass m=4.2kg is suspended from the...
  7. P

    Calculating Rotational Inertia and Speed of a Square Plate

    Homework Statement A uniform square plate ABCD has mass 0.8 kg and side length .8 m. The square is pivoted at vertex D and initially held at rest so that sides AB and CD are horizontal (see the diagram). After it is released, the plate swings downward, rotating about the pivot point...
  8. L

    Simulation of rotational spectra of a symmetric top

    Hello fellow physicists, I have a query about a practical matter. I'm trying to simulate the rotational spectrum of a symmetric top and so far I've been able to produce a stick spectrum of it. My first problem is that the lines do not exactly match the positions of the peaks but my biggest...
  9. A

    Solve Rotational Problem 3: Max Angle for Rod+Clay

    Homework Statement A 75 g 30 cm long rod hangs vertically on a frictionless, horizontal axle passing through its center. A 10g ball of clay traveling horizontally at 2.5 m/s hits and stick to the very bottom tip of the rod. To what maximum angle measured from the vertical, does the rod with...
  10. A

    Max Angle of Rod w/ Clay Ball: Rotational Problem 2

    Homework Statement A 75 kg , 34 cm long rod hangs vertically on a frictionless , horizontal axle passing through its cener. A 15 g ball of clay traelling horizontally at 2.2m/s hits and sticks to the very bottom tip of the rod. To what maximum angle , measured from vertical , does the rod (...
  11. A

    Simulating opposing rotational forces at different points on structure

    Hi, I am trying to simulate a tangential force acting on a point on a structure and the corresponding opposing force caused by the moment of inertia of a mass at a different position. In this image the structure rotates around point c and there is a vector out of mass m opposing the...
  12. A

    Solving Rotational Problem: Satellite Elliptical Orbit, Torque & Speed

    Homework Statement A satellite follows an elliptical orbit. The only force on the satellite is the gravity atraction from the planet. The satellites speed at point A is 8000m/s, and it is 6000km away, Point B is 24000km east of the planet, and Point C is component vector 9000ikm+12000jkm...
  13. A

    Rotational Dynamics / Moment of Inertia Question

    Homework Statement An oxygen molecule consists of two oxygen atoms whose total mass is 5.3x10^-26 kg and whose moment of inertia about an axis perpendicular to the line joining the two atoms, midway between them, is 1.9 x 10^-46 kg*m^2. From this data, estimate the effective distance between...
  14. Eagle9

    Upper limit for black hole’s rotational speed

    From wikipedia: Rotating black hole So, the black holes have got the upper limit for rotating? Could somebody explain me why? I can understand one reason: due to special theory of relativity the event’s horizon’s circular/linear speed cannot be more than speed of light, right? Or maybe there...
  15. P

    Translational and rotational forces in a vehicle moving along a string

    Hi. I've been working on a project of angle stabilization for a vehicle moving along a string, looking like this: The propulsion system is connected to the central wheel, while the outer two wheels are used for support. I've observed that during acceleration the vehicle rotates. I...
  16. Femme_physics

    Converting a screw's linear speed to rotational

    Suppose I have a screw that makes some sort of frictionless ball bearing move at 0.3 m/sec That means that to find the RPM of the screw I do pi x mean diameter of the screw x rotation per minutes / 60000 and I get the answer?
  17. S

    Rotational Intertia of a rotating Space Station

    Homework Statement Four rockets attached to a (wheel) space station exert a force of 65.5N to rotate it . The space station's angular velocity is increased at a constant acceleration of 3.63 x 10-3 rads-2. Each rocket is 11.2m away from the centre. Calculate the rotational inertia of the...
  18. C

    Rotational Kinetic Energy of Disks

    Homework Statement A disk with a mass of 4kg and a radius of 2m is free to rotate around an axis that passes through the center of the disk and perpendicular to the plane of the disk. The rotational kinetic energy of the disk is increasing at a constant rate of 20 J/rad; that is, the energy...
  19. D

    Rotational energy conservation

    Hi, I am a little confused about the energy conservation of a pin ended free falling rod. When i try to derive energy conservation equation i am not sure including angular and linear velocity at the same time. I try to visualize the problem in the attached picture and put my derivation also...
  20. D

    How many different velocities for this rotational mechanical system?

    Homework Statement I need to write the equations of motion for the mechanical system below. So I need to know how many velocities there are in the system, the answer key says there's only 4 but shouldn't there be 5? I am unsure if the J3 mass has it's own velocity from the point between K_2 and...
  21. B

    Kinetic rotational energy of a bar hooked to a coil

    I have solved an exercise and I'd like to know if my proceeding about finding kinetic energy is correct or not, because this is the first time that I "meet" a situation like this. "A bar has mass M and length l. Its extremity A is hooked to a coil (with length at rest l0), its extremity B is...
  22. howabout1337

    Do the Large Hadron Collider take earth's rotational speed?

    so according to wiki: protons have a Lorentz factor of about 7,500 and move at about 0.999999991 c, or about 3 metres per second slower than the speed of light (c) If we consider speed of Earth's rotation or speed at which two galaxies approach each other (collision or otherwise)?
  23. R

    Rotational Equilibrium Homework Help

    Homework Statement Answers were told to us to be F = 2.91 N Ft1 = 13.32 N Ft2 = 3.36 N Homework Equations Fx = Ft2 cos(θ) - F = 0 Fy = Ft2 sin(θ) + Ft1 - Fg = 0 Torque equation -FgDg - Ft2D1x cos(θ) + Ft2D1y sin(θ) = 0 The Attempt at a Solution I plugged in all of the information i had...
  24. A

    Problem on rotational dynamics

    Homework Statement Given a rod of length 'l' placed upright on a smooth floor.A slight disturbance causes it to fall.Now required is the velocity with which the COM falls down when the rod makes angle θ with horizontal. The Attempt at a Solution now let the middle portion of the rod be...
  25. B

    What Happens to Angular Velocity When a Disc is Dropped onto a Rotating Hoop?

    1. A hoop with mass 2.0 kg and radius 1.5 m is rotating with initial angular velocity of 5.4 s-1. A disc with the same mass and radius is dropped on top of the hoop so that the centers coincide. What conservation law applies here? What assumptions must you make to apply it? What is the final...
  26. J

    Rotational Kinetic Energy of Body in another body reference frame

    I have two rigid bodies floating in space that are kinematically constrained by a joint (think of a 2 dof link mechanism floating in space). I have a body fixed reference frame on each rigid body plus the global space-fixed reference frame. The first rigid body is in the space-fixed...
  27. P

    How Does Friction Affect Energy Conservation in Rotational Motion Experiments?

    Homework Statement We performed a small experiment in class which had us attach a mass to a string which hung on a pulley which led to a rotating object. We were then told to write down a conservation of energy equation stating that the initial energy is equal to the final energy. We were...
  28. Y

    Rotational Motion Question with Work Energy Theorem

    Homework Statement A 392-N wheel comes off a moving truck and rolls without slipping along a highway. At the bottom of a hill, it is rotating at 25.0rad/s. The radius of the wheel is .6m and its moment of inertia about its rotation axis is 0.800MR2. Friction does work on the wheel as it...
  29. L

    Rotational motion problems involving radians

    Homework Statement The professor gives us an exam preview where he hints at the types of problems via the picture. Attached is the preview. I have a question about pictures 1 and 2. It's probably a problem that involves rotational and translational energy, conservation of energy. If it's...
  30. F

    How Does Rotational Momentum Apply in a Combined Linear and Angular System?

    1. Problem statement 2. Related equations I = bmr^2 Energy equations (linear and rotational) 3. Attempt Part a) I know that the distance or height traveled by the box is [h - d] because center of the mass of box is just d. Initial kinetic energy of the box and cylinder is 0 and if only...
  31. F

    Rotational and angular speed problem

    Homework Statement A constant force of 50 N is applied tangentially to the rim of a solid disc with a 60cm radius. The wheel has a moment of inertia of 40 kg m^2 a) what is the mass of the disc? b) 4 seconds after starting from rest, what angular speed does it have? c) How many...
  32. G

    Rotational energy and flywheels

    Homework Statement Hey guys I have two questions. The first one I'm not sure, while the second one, I have some idea but don't know how to proceed with answering the question. 1. A rapidly spinning flywheel has been suggested as an energy storage mechanism for cars. Let's consider a 300kg...
  33. S

    Rotational Motion of a toy airplane

    Homework Statement We were given a video...I'm not sure if you can post video links otherwise I would...but it's a video of an airplane on a string flying in a circular motion. On the top of the string you can see that the tension of the string is 6.5N. and it is flying at an angle of 50°...
  34. M

    Rotational Energy and momentum help

    Homework Statement A uniform rod of length L1 and mass M = 0.75 kg is supported by a hinge at one end and is free to rotate in the vertical plane (Figure). The rod is released from rest in the position shown. A particle of mass m = 0.5 kg is supported by a thin string of length L2 from the...
  35. C

    Rotational Mechanics-Symmetric body goes up an incline.

    Homework Statement Find the velocity with which a symmetric body of radius "R" starts to roll up an inclined plane if it was rolling without slipping on a horizontal plane with velocity "v1" and reached the incline. Angle of inclination of plane with horizontal=θ Radius of gyration of the...
  36. J

    Terminology in rotational kinematics: distance vs displacement

    I'm trying to learn some physics on my own, using the internet as my main source of information. Now, I'm a bit confused about some terminology, and I can't find anything about it... Distance vs displacement in rotational kinematics! Is there a similar difference as in linear kinematics...
  37. N

    Rotational motion on pulley system

    Homework Statement A string passing over a pulley has a 3.80-kg mass hanging from one end and a 3.15-kg mass hanging from the other end. The pulley is a uniform solid cylinder of radius 4.0 cm and mass 0.80 kg. If the bearings of they pulley were frictionless, what would be the acceleration...
  38. X

    Prove rotational invariance leads to conservation of ang. momentum

    Homework Statement Noether's theorem asserts a connection between invariance principles and conservation laws. In section 7.8 we saw that translational invariance of the Lagrangian implies conservation of total linear momentum. Here you will prove that rotational invariance of L implies...
  39. Sneakatone

    Find watts from rotational kinetic energy

    a)I used the equation KE=1/2Iw^2 I=mR^2 ---> 1.5x10^30*20000^2 w=2.1*2pi KE=1/2(1.5x10^30*20000^2)(2.1*2pi)^2=5.2x10^40 J t=2.1 rev/s / 1.4x10^-15 rev/s^2=1.5x10^15 seconds 5.2x10^40 J/1.5*10^15 seconds =3.4x10^25 watts B)1.15*10^15 s=1.1*10^18 years I feel like this method is...
  40. sankalpmittal

    Rotational Mechanics - Question

    Homework Statement A uniform rod of length "L" is kept vertically on a smooth horizontal surface at a point "O". If it is rotated slightly and released, it falls down on the horizontal surface. To what distance will the lower end of the rod "shift" from point "O" ? Note : The answer in the...
  41. H

    The concept of rotational equilibrium

    Here is a text from my Physics Book : The net external torque on the object about any axis must be zero for it to be in rotational equilibrium. I divide the torques into two categories, anticlockwise and clockwise. (This approach works fine for 2-D objects but will it work for 3-D objects...
  42. 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...
  43. D

    Conservation of energy (and rotational kinetic engery)

    This is not a homework question. An adult exerts a horizontal force on a swing that is suspended by a rope of length L, holding it at an angle θ with the vertical. The child in the swing has a weight W and dimensions that are negligible compared to L. The weights of the rope and of the seat...
  44. 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...
  45. 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...
  46. 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...
  47. L

    Rotational invariance and degeneracy (quantum mechanics)

    Homework Statement Show that if a Hamiltonian H is invariant under all rotations, then the eigenstates of H are also eigenstates of L^{2} and they have a degeneracy of 2l+1. Homework Equations The professor told us to recall that J: \vec{L}=(L_x,L_y,L_z)...
  48. M

    How Is the Driving Torque Calculated for a Hoist Drum in Rotational Dynamics?

    A mine cage of mass 4 tonne is to be raised with an acceleration of 1.5m/s^2 using a hoist drum of 1.5m diameter. The drum’s mass is 750kg and its radius of gyration is 600mm.The effect of bearing friction is equivalent to a torque of 3kNm at the hoist drum. What isthe driving torque required...
  49. 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...
  50. 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...
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