What is Precession: Definition and 258 Discussions

Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis. A motion in which the second Euler angle changes is called nutation. In physics, there are two types of precession: torque-free and torque-induced.
In astronomy, precession refers to any of several slow changes in an astronomical body's rotational or orbital parameters. An important example is the steady change in the orientation of the axis of rotation of the Earth, known as the precession of the equinoxes.

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  1. I

    Angular frequency precession of spinning top

    Homework Statement im doing a sipnnig top question and i have got an answer for the precession angular velocity this site shows a good example of what i did: http://hyperphysics.phy-astr.gsu.edu/hbase/top.html and so i have gr/K2w if i sub in I=mK2 but i need to find the angular...
  2. M

    Continuous application of Lense-Thirring precession: flyby anomalies

    Not sure where to put this, but if it's wrong, sorry... I just looked at the Nieto, Anderson paper on arXiv: arXiv:0907.3418 "Earth Flyby Anomalies" Funnily enough, it's about anomalies in the velocity of probes doing Earth flybys! This has hit the scientific news (New Scientist this...
  3. B

    Direction of vector precession

    Not a homework question! Consider a proton and coordinate system immersed in an upward pointing external B-field. If the orbital magnetic number m (sub l) is a positive hbar then the vector precesses counter-clockwise about the positive z axis. 1. If m (sub l) is a negative hbar then...
  4. K

    Precession: Explaining the Linear Motion of a Spinning Wheel

    Probably an easy one... So, I understand the idea of precession on a gyroscope: we've got the angular velocity vector, the angular momentum vector (same direction but times the inertia tensor), then a torque is applied => change in L in the direction of torque. I'm thinking of the example...
  5. T

    Bike wheels forced precession

    Homework Statement Bike has leaned, passing via corner. Centrifugal forces ( m*(V*V/R)*sin(alpha) ) are trying to upright the bike, gravity forces ( m*g*cos(alpha) ) to lean it further, so the balance lean angle comes tg(alpha) = V*V/R/g, where V is bike speed, R is curve radius, g is...
  6. snoopies622

    About rotation and precession

    I was just reading about torque-free precession and having difficulty seeing how an object's angular velocity vector could at any moment point in a direction that is different than the direction of its angular momentum vector, since that is not possible for an isolated particle \vec...
  7. J

    Two Types of Precession: Are They Both Examples of the Same Phenomenon?

    It occurred to me recently that there are two forms of precession. If you hold a spinning bicycle wheel and force the axis of rotation to tilt on its side, this will induce a torque tending to spin the wheel about a vertical axis. This is in accord with the fact that the change in angular...
  8. E

    Effect of gravity on the precession rate of a gyroscope

    Homework Statement A certain gyroscope precesses at a rate of 0.60 rad/s when used on earth. If it were taken to a lunar base, where the acceleration due to gravity is 0.165 g, what would be its precession rate? Homework Equations Is the precession rate directly proportional to the...
  9. C

    Solve Gyroscopic Precession Homework: Find Time for 1 Precession

    Homework Statement A gyroscope consists of a rotating disk with a 48.7cm radius suitably mounted at the midpoint of a 12.2cm long axle so that it can spin and precess freely. Its spin rate is 975 rev/min. The mass of the disk is 1.14kg and the mass of the axle is 130g. Find the time required...
  10. M

    What Torque Causes Earth's Precessional Cycle?

    Homework Statement The Earth's axis of spin precesses just like that of a top or a gyroscope. (This is why the North Star moves away from the north over many centuries.) The cause is the torque on the Earth due to the gravitational pull of the moon and the sun on the Earth's equatorial...
  11. N

    Explaining Mercury's Precession: Layman Terms

    Could someone explain in layman terms the current thinking on why the orbit of Mercury precesses? Presumably, it is not precessing in a gyroscope sense but the perihelion of the orbit just advances in the same plane.
  12. H

    Spin Precession in a Magnetic Field

    I'm having a mental block on this and I was hoping that someone could help me. A little background Consider a spin-1/2 particle in static, homogeneous magnetic field, \vec{B}=B \hat{k} The Hamiltonian is H=-\vec{\mu}\cdot\vec{B}=-\gamma B S_{z} where \gamma is the gyromagnetic...
  13. R

    Eccentricity & GR precession; Mercury vs. GPB

    Eccentricity & GR precession; Mercury vs. GP-B How big a factor is the Eccentricity of Mercury orbit in contributing to its precession? GR precession has been confirmed in the Gravity Probe B orbit even though it has an eccentricity of zero. The GP-B used a gyroscope to take the place of a...
  14. J

    Gyroscope- Angular Speed, Rotational Kinematics, Precession

    Gyroscope-- Angular Speed, Rotational Kinematics, Precession Homework Statement A Gyro Stabilizer. The stabilizing gyroscope of a ship is a solid disk with a mass of 6.50×10^4 kg; its radius is 2.30m, and it rotates about a vertical axis with an angular speed of 500 rev/min. 1) How much...
  15. F

    Precession angle per orbit of perhelion precession mercury

    Many derivations of mercury precession angle per orbit \Delta\Phi, equate this to extra angle per orbit \delta in excess of 2\pi that is \delta = \Delta\Phi But I am getting this relation \sqrt{4\pi\delta}= \Delta\Phi from arc length of helix and circular orbit. What am I doing...
  16. J

    Correct definition of planetary precession

    Hello. Can anyone please provide me with an authoritative definition of planetary precession? Any link to an authoritative source would be best. I did do my googling first. I tried to provide my search results but an ostensibly spam-blocking feature does not allow me to post the links because I...
  17. X

    Electron Precession versus Proton Precession in a Magnetometer?

    Hello, Why is it that electron precession is not used in addition to proton precession in a proton precession magnetometer? It seems to me that when the frequencies are emitted as the protons precess that the electrons would do precessing at the same time and provide a secondary frequency to...
  18. S

    Why does symmetry lead to a restoring force in precessional rotation?

    I know it's just a mental block - for some reason I can't get the phrase "restoring force" out of the ongoing debate in my noggin. But this is a question about symmetry specifically, and the notion of a force appearing because of an asymmetry, or "symmetry-breaking". The simplest notion I...
  19. J

    Why Does Neutron Precess Despite q=0?

    We all know that the magnetic moment is (gq/2m)J, so then why does a neutron precess in a magnetic field if q=0? This should cause the Hamiltonian to be 0.
  20. B

    Larmor Precession: Understand Charge Orbitting Fixed Charge

    i'm familiar with terminology used to denote rates of change in inertial and rotational frames, and the equation that links the two quantities, but working through a derivation/thought experiment to describe charge orbitting around another fixed charge in a weak magnetic field, it results in...
  21. B

    Gyroscope precession derivation

    alrite I am new on this forum...just discovered it...pretty awesome ok, I am looking over notes from a classical physics course i did, and I've just covered rigid bodies, and literally just got through the inertia tensor, principal axes and all that good stuff. theres a step in the...
  22. D

    Does Thomas Precession violate angular momentum conservation?

    Suppose we have an accelerated rigid body that possesses angular momentum. Then the body will undergo Thomas precession, and if the angular momentum vector of the body is not aligned with the axis of the Thomas precession, the angular momentum vector of the body will precess when viewed in an...
  23. U

    Precession of the earth's axis

    I remember an analogy with a child's spinning top, that does not rotate in a fixed axis but the axis makes a precessional movement. But the spinning top is sitting on something, it's getting a force from below that's not aligned with its weight, so this force has a torque, etc etc (can't...
  24. D

    What Determines the Precession Angle of an Electron in a Magnetic Field?

    Hi again, It is well known the precession frequency of a free electron under a magnetic field, know as the Larmor frequency. However, i have not found any mention to the angle between the spin magnetic moment and the magnetic field. If the angle changes, to keep the same frequency the rotation...
  25. J

    Precession: Deriation of formula

    Please see this link first: http://en.wikipedia.org/wiki/Precession#Classical_.28Newtonian.29" How do they get to the formula \textbf{wp} = \frac{Q}{I*w} I also note that I*w = L (angular momentum). How do they get to that equation? I've thought and though, I just don't know how. I really...
  26. K

    Wat are the units of angular velocity of precession?

    Homework Statement What are the units of angular velocity of precession? I've looked evrywhere and can't find out. Homework Equations The Attempt at a Solution In my answer to a question, by putting units into the equation i think I am getting units as rad^-1 s^-1 but not sure...
  27. O

    Schwarzchild solution and orbit precession

    In the Schwarzschild geometry of a static spacetime, elliptical test-particle orbits precess at a rate that (famously) agrees with observations of the inner solar system. Yet the model system considered is isolated, spherically symmetric with only the radial coordinate non-Euclidean. I...
  28. L

    Heisenberg Equations of Motion, Solving for S(t) in Spin Precession problem

    Problem Consider the spin precession problem in the Heisenberg picture. Using the Hamiltonian H=-\omega S_{z} where \omega=\frac{eB}{mc} write the Heisenberg equations of motion for the time dependent operators S_{x}(t), S_{y}(t), and S_{z}(t). Solve them to obtain \vec{S} as a function...
  29. N

    Precession in a central potential

    Homework Statement Consider the following parametrization of an orbit in polar form, \ell u = 1 + e \cos[(\phi -\phi_0)\Gamma] where u = 1/r. I'm trying to find the shift in the angular position of the periapsis after one complete orbit. The Attempt at a Solution Choose axes so that the...
  30. T

    Precession of ellipsoid Question

    Homework Statement A uniform symmetric ellipsoid (Mass M) has a large semi axis c and small semi axis a. A particle of mass m<<M is moving along a straight line parallel to the x-axis with speed v(i). Its y-coordinate is a/2 and its z-coordinate it c/2. After an inelastic collision, it sticks...
  31. MathematicalPhysicist

    How Does Frictionless Surface Affect Gyroscope Precession?

    1)i have this problem, we have a toy gyroscope, which its pricnipal moments of inertia are known, spins around its axis of symmetry with angular velocity w, and it's tilt with angle a from the vertical on a smooth table (i.e frictionless table). i need to find the precession frequency? im given...
  32. H

    Free-floating top; relation of precession angle and precession and spin rates

    Does anyone know of a formula describing the relationship between precession rate, precession angle, and spin rate for a top (or gyroscope, or any hard, non-spherical object) spinning freely, in zero gravity? All the analyses I've been able to find are for tops under constant torque (gravity)...
  33. R

    All spun out by the precession of tops

    hey anyone have any light to shed on the following: trying to revise a bit of the old classical mechanics this week and stumbled on a question about spinning tops that i couldn't do.. the question gives you the dimensions of the top and asks you do sketch the subsequent motion of the top...
  34. W

    Don't quite understand precession

    I don't quite understand WHY a gyroscope precesses the way it does. I'll set up an example in order to ask the questions I need. Lets say you have a spinning bicycle wheel suspended at one end of its hub by a string. Due to the angular momentum of the spinning wheel, the wheel will precess...
  35. R

    How Is the Direction of Gyroscope Precession Determined?

    Hi, It asks me to state whether the direction of the gyroscope precession is clockwise or counterclockwise (see attachment). I am confused as to how they determined from the top view (on the left) that the direction of angular velocity and angular momentum were pointing towards the left...
  36. T

    Precession of the perihelion - Schwarzschild metric

    Hi everyone! I was trying to solve this question following the Hartle's book (Gravity: an introduction to Einstein’s general relativity) , exercise 9.15, but I don't know how to do the expansion of (1-2GM/c^2r) in powers of 1/c^2... I know this sounds easy, but I couldn't get the expression...
  37. L

    Change in the precession angle

    Hi. I have: A 3 kg bicycle wheel rotating at a 2484 rev/min angular velocity has its shaft supported on one side, as show in the figure. When viewing from the left (from the positive x-axes), one sees that the wheel is rotating in a clockwise manner. The distance from the center of the wheel to...
  38. T

    Precession axis of a spinning top

    Hi, I have a little question The precession axis of a spinning top is represented vertical in every pages I have seen. Why is that? Isn't that axis just a virtual (resulting from spinning of the precession axis) precession axis, because the precession axis must be perpendicular to momentum...
  39. N

    Exploring Precession and its Role in Hindu Scripture

    i was just finishing my project and i got a idea maybe it is valid maybe not could ya'll judge it and opine on it thank you here it is: i heard that there is something know as preccession and that in another 14000 years the Earth shall point towards vega that is we have crossed 12000 years, so...
  40. T

    Tidal force, torque and precession

    imagine a sun and a planet, both rigid and perfectly spherical. the distance between the center of mass of these two bodies is much greater than the radius of both bodies. considering Newton's inverse square law of gravity: now, due to the non-uniform nature of this gravity, different parts...
  41. P

    Gyroscope precession - WHY? (What's the cause?)

    «(...) a torque τ applied perpendicular to the axis of rotation, and therefore perpendicular to L, results in a motion perpendicular to both τ and L. This motion is called precession.»(http://en.wikipedia.org/wiki/Gyroscope) Why does this happen? Assumpting this makes all further calculus...
  42. T

    Vector math for precession?

    Trying to find the vector math for gyroscopic precession - all web sites I've seen that deal with analysis don't include direction of rotation as a vector and I can't find a discussion in my texts on the subject. The question I'm trying to answer is whether two opposite rotating discs of...
  43. A

    Torque Free Precession: What, Why & How

    What is torque free precession, and why does it occur? I'm surprised that it predicts that a solid cylinder rotating in space would "wobble" a bit. Why is it not possible to have a cylinder rotating around a constant axis? I understand how it comes from Euler's equations, but I'm not too sure...
  44. R

    How is the Precession of Mercury's Perihelion Calculated and Explained?

    precession of perihelion for Mercury (arc s/century) 5025".6 Coordinate 531".4 Gravitational tugs of the other planets 43".0 General relativity The first two were well known with the unexplained 43” a problem until it was explained by GR...
  45. fargoth

    Magnetic Precession and Photon Absorption

    In my understanding, when a nuclei absorbes a photon with the right freq it changes its spin... now, if this atom is in a magnetic field B on the Z direction, its magnetization vector is precessing around the Z direction, and after absorbing a photon it changes its angle relative to the Z axis...
  46. P

    Gravity Probe B: Gyroscope Orientation and Precession

    I was looking at some web sites about the Gravity Probe B. Some show the spin axes of the gyroscopes oriented perpendicular to the Earth or else in the direction of movement of the satelite. Wouldn't these orientations cause lots of precession? I'd expect the gyroscopes' axes of rotation to...
  47. I

    Help with precession experiment

    I want to produce precession by the use of a bycicle wheel and a spinning chair. Whats the best position of the wheel both with respect to the vertical and horizontal to cause the maximum precession?
  48. I

    Is the force produce by precession reactionless?

    Some studies point so. Besides i suposse it´s not against classical physics since nobody important said that spinning forces had reaction
  49. I

    Is Precession Timeless in Cosmology or Earth Science?

    I read it somewhere and it would make sense if you considered time as spin. What do you think?
  50. P

    Torque-Free Precession of Spinning Plates

    I am trying to figure out which way a spinning dinner plate (idealized as a disk) precesses when you toss it in the air. I can figure out the rate of precession in terms of the spin rate and the angle the spin axis makes with the precession axis. I believe it is \Omega_{pr} \cos{\theta} = 2...
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