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. G

    Precession: A picture using only forces

    Hi, If the axis of a spinning top isn't vertical, it starts to precess. I'm perfectly familiar with the explanation using torque, angular velocity and momentum vectors, then the direction of the precession comes out just by taking a vector product. However, to me it's absolutely not intuitive...
  2. goonking

    Precession Period: Calculate Speed

    Homework Statement Homework Equations this was a formula I just found on Wikipedia, but it seemed to be right for this problem. The Attempt at a Solution so we have the diameter of the of the wheel = 0.7 m mass of wheel = 0.25 kg distance of the rod attached = 0.2m angular velocity of...
  3. V

    Precession of Mercury and period of rotation

    HI - we know that the orbit of mercury precesses (I hope I am using the right terminology here). Which basically means that the orbit seems to undergo some sort of rotation in the ecliptic plane. Does this also mean that the period of Mercury's orbit as seen from the Earth is not uniform but...
  4. S

    Explanation of Torque in the precession of a top.

    Homework Statement I'm reading through Taylor's Classical Mechanics, and I am confused by one sentence in section 10.6 The image he is referencing is this while the text is here. Specifically the statement "the gravitational torque is clockwise" Using the right hand-rule, I run my...
  5. S

    Rate of precession caused by mountain on spherical earth

    Homework Statement R = 4000mi phi = 60 Me = 5.972E24 kg Mm = 5.972E16 kg distance of procession = 100 mi Homework Equations I know the answer is supposed to be ~1010 years. I also know what I am trying to do is have that e3 axis be pointing straight up, then when the mountain is placed on...
  6. T

    Why is the change in angle of precession equal to dL/L?

    If a rapidly rotating gyroscope attached to a perch is released in a horizontal position -- that is, so that the axis of the gyroscope is horizontal -- the gyroscope will precess around it's perch. Let L represent its angular momentum. Let dL represent a small change in that momentum. Let dA...
  7. H

    Precession of Earth's axis and alignment with stars

    I picked up a book about the pyramids at Cheops. (Relax, it wasn't a crackpot work.) It said that the pyramid was aligned with the star Polaris, and that Sirus and Orion may be sighted through some of the ventilation shafts. Now the pyramid is aligned with true north. It the time of the...
  8. M

    Why is a gyroscope's precession fastest at 45 degrees?

    I did an experiment in which I varied the starting angle of elevation of a gyroscope. I noticed that at 45 degrees, the precessional period (amount of time to perform one spin) is the lowest, while at 0 degrees and 75 degrees, the precessional period is higher. If I plotted this on a graph, it...
  9. H Smith 94

    Gyroscopic precession: What provides the centripetal force?

    Hi there! I've been searching the internet for hours trying to find a decent explanation to this question. I'm thinking particularly of the example of a precessing spinning top. (Note: I own this diagram. Please do not use it without direct and written permission.) So when the top is tilted...
  10. G

    Thomas precession Goldstein/Eisberg versus Taylor/Wheeler

    I've looked at Taylor and Wheeler's Spacetime Physics Example 103 on the Thomas Precession and also the discussion of Thomas precession in Eisberg and Goldstein (3rd edition). Both treat the rotation angle gotten by the addition of 2 non-collinear velocities. The answers they get are...
  11. kmm

    What is the source of additional energy in a precessing gyroscope?

    I'm trying to think about gyroscope precession in terms of energy, and I'm a little confused. If you hold the spinning gyroscope at some tilt so that it doesn't precess, it will have energy associated with it's rotation. When you let it go, it will now have additional energy due to the...
  12. G

    Initial Gyroscopic Precession Using Forces

    I think I more or less understand how a gyroscope precesses--at least mathematically and in terms of torque/angular momentum. My question here is: how does the gyroscope start precessing in the first place? The external forces on the center of mass are entirely vertical. Given that Newton's...
  13. C

    What is the value of k in the Moon's orbital precession?

    I want to compute the precession of the Moon's orbital plane, sometimes called as the precession of nodes. I assume simple harmonic motion; the Moon orbit lies in a plane X-Y, so it oscillates along z: z'' = -kz By definition k = w^2; and we know already: w = 2pi/18.6y; because the period of...
  14. T

    Gyroscope Precession: Understanding Angular Momentum & Energy

    Hello. I know there are quite a few threads about this, but I couldn't find what I was looking for. This topic has been driving me crazy over the last couple of days. I know the cause behind the precession. It's because the torque due to gravity about the pivot tends to rotate the already...
  15. D

    Understanding Torque in Gyroscopes: A Question of Reference Frames

    I am a college student currently working on a physics project involving gyroscopes. Using the equation below (taken from Wikipedia), am I correct in assuming that dL/dt is the torque of the flywheel and that ω x L is the torque of the gyroscope around the axis of precession?
  16. O

    Can Numerical Simulations Accurately Predict Orbital Precession?

    If we had a literal two body system (point masses M and m), with one orbiting the other according to Newton's Law of gravitation, would there be orbital precession? Or would they map out the same ellipse each time?
  17. R

    Precession of relativistic orbit in pure inverse-square force

    PROBLEM: Show that Special Relativity predicts a precession of π(GMm/cl)2 radians per orbit for any elliptic orbit under a pure inverse-square force. where G is gravitational constant, M is mass of larger body, m is mass of smaller orbiting body, c is speed of light and l is angular momentum...
  18. A

    Orbit Precession Angle: Find & Condition for Cycles

    the problem says: "consider a particle with orbit ##r(\phi)=\frac{r_0}{1-\epsilon \cos (\beta \phi)}## ##\epsilon \in ]0,1[## and ##\beta=cte## a) Find the precession angle. b) What is the condition to the trayectory is totally cyclic?? __________________ I don't understand why i calculare...
  19. S

    Chandler wobble: nutation or precession?

    Wikipedia claims that the Chandler wobble (a deviation of the angular velocity vector of the Earth with respect to the principal axis) is a nutation (see http://en.wikipedia.org/wiki/Chandler_wobble). But suppose we choose our inertial frame so that the Earth's angular momentum points in the +z...
  20. N

    Puzzling precession of the torque-free symmetric top

    Hello everyone, as I know the regular precession of torque-free symmetric top is such a cliche, I'll try to keep derivations short. The goal is, as I pointed out, to inspect a behaviour of the torque-free symmetric top in terms of precession rate, rotation rate and nutation angle. One way is to...
  21. 4

    Spin precession vs alignment in magnetic field

    The spin of an arbitrarily oriented electron precesses in the presence of a magnetic field (see Feyman lectures 10-7). The energy states also split due to magnetic fields (see Feynman lectures 12-4). I am trying to understand how to think about spin precession, spin flipping, and spin...
  22. M

    Astronomy; Precession data co-ordinate systems

    Homework Statement Use a coordinate conversion application to roughly map out the amount of precession in coordinate positions (R.A and Declination) in the sky between 1950 and 2000. Homework Equations I can easily find a converter on the internet The Attempt at a Solution I...
  23. D

    The Mystery of Thomas Precession in Weinberg's Book

    I am planning to start self studying GR and, before choosing a better book to use, I have been flipping through an old copy of Weinberg's book (Gravitation and Cosmology) and came upon something that is not making sense to me. I assume that I am missing something obvious. When he talks about...
  24. WannabeNewton

    Spin precession Killing fields

    Hello. I was going through the problems in the angular momentum chapter of the text "Problem Book in Relativity and Gravitation"-Lightman et al in preparation for a project and I came upon part (c) of problem 11.10. It basically starts with a family of observers with 4-velocity ##u^{\mu} =...
  25. W

    How do I calculate the torque of precession for a spinning wheel?

    Is it just equal to the external torque acting on the spinning wheel?
  26. L

    Gyroscopic Precession Question

    Veritasium posted a video on his YouTube channel called "Gyroscopic Precession." () In the video he explained how spinning the wheel caused the torque tho point toward "the camera" at 90° to the angular momentum. My first question is how and why does the torque point perpendicular to the wheel...
  27. W

    Epicyclic motion and precession

    Imagine I am standing but not moving forward/backward, but I am rotating my body about my own axis. Now imagine if I moved in a circular path as I was spinning on my own axis. Is this considered to be precessing (assuming the axis of rotations are always in the z direction)? My friend...
  28. Y

    Intuitive understanding of Thomas precession

    There are various explanations for Thomas precession in the literature and I would like to come to a deeper understanding of the cause for this precession, so that maybe I can understand better whether Thomas rotation is applicable to the precession of a gyroscope orbiting around a gravitational...
  29. S

    Hall's solution for Mercury's precession

    Hall showed that a slight increase in the radius exponent in Newton's equation would cause precession. What would the result be if the exponent was slightly less than 2.
  30. kmm

    Why does Larmor precession appear to go against the right hand rule?

    For some reason, I don't understand the direction of larmor precession. Torque is: \mathbf{\Gamma} = \frac{d \mathbf{L}}{d t} = \mathbf{r} \times \mathbf{F} As an example, I understand with a gyroscope, using the right hand rule and with angular momentum in the direction as shown in this...
  31. T

    Torque, produced by gyroscopic precession

    Hello All, When a spinning gyroscope with two degrees of freedom sits on the surface of the Earth, with its spin axis perpendicular to the Earth and its inner gimbal aligned east to west, it will precess. What I would like to know is, how much torque is produced about the east-west axis when...
  32. J

    Explaining gyroscopic precession with linear vectors?

    For example, an explanation as to why a gyroscope resists movement is because every point on the wheel has a linear velocity of a certain speed and it would take a sufficient amount of force to change its direction. So could you also explain gyroscopic PRECESSION using only the linear...
  33. U

    How did they get this precession frequency of this gyroscope?

    To summarize: 1. The solenoid is supplied with an AC voltage. 2. Produces an AC magnetic field out of the page 3. Exerts an AC magnetic force on the Nb-Plate that's placed just outside of one end of the solenoid 4. There is a fluid circulating in the torus, with angular momentum L in the...
  34. I

    Thomas Precession, Angular Momentum, and Rotating Reference Frames

    If any of you have the Third Edition of Classical Electrodynamics by John David Jackson, turn to section 11.8, as that's where I'm getting all this from. If not, you should still be able to follow along. In said section, Jackson gives us this equation that relates any physical vector G in a...
  35. T

    Question about precession in the case of frisbees

    So, I was trying to figure out the physics of frisbees. When you throw a frisbee at the ground at an angle (such that the side to the left of you, assuming you are right handed, hits the ground first), then it will suddenly skip up and fly upwards (Youtube has some great videos of it, for anyone...
  36. I

    Gyroscopic Precession (Relationship with ωspin and ωprecession)

    Homework Statement I am trying to find the relationship between the rate of precession(ωprecession) and the angular velocity of the wheel(ωspin). Here is a video that explains the problem well: http://www.youtube.com/watch?v=ty9QSiVC2g0 Homework Equations $$L = r X P = Iω$$ $$\tau = r X F$$...
  37. O

    Understanding Mercury's Precession

    I was recently given a lab to work at home but I am having trouble understanding the formulas that they have used. The link to this lab Assignment: http://classroom.sdmesa.edu/ssiegel/Physics%20197/labs/Mercury%20Precession.pdf My problem relies to Query #1 of the lab assignment, with the...
  38. A

    Correct approach for modeling the motion of a gyroscope?

    Its a long time since I have done any mechanics and today I thought I would like to work out the equations of motion for a gyroscope. So I tried to put up a Lagrangian for a simple system (on the picture) of a rod of length L that is free to rotate about a pivot which has a flywheel (the red...
  39. S

    Precession Period of A Gyroscope?

    Hi I am doing my geodesy lab and don't really know how to calculate period of gyro? How the Precession Period of A Gyroscope is calculated? given D= diameter of gyro, f= spinng freq w= weight , g =9.8 and distance d= distance between center of gyro and for example Sun Assumption...
  40. K

    Nodal Precession Rates of Solar System Planets

    Good Day Everyone, I am trying to find out the rates at which the inclinations of the Solar System's planets change. E.g. Earth's inclination to the invariable plane cycles every 70,000 years. I believe its called the Draconitic Period or Nodal Precession Period. I'm trying to find out...
  41. N

    Understanding Precession in B Field: Torque and Electron Motion Explained

    There is a problem about precession in general that I am trying to understand, and it can be exampled by electron orbiting around nucleus in external \vec{B} field. We could consider electron motion as loop current which is characterized by the magnetic moment \vec{μ}...
  42. Low-Q

    Precession - the cause. Gyros.

    I have a question about precession. I have seen a few videos on youtube. A bicycle wheel that is attached to a thread on one side. The wheel is aligned upright, and spun by hand. The "experimentist" release the wheel, and precession starts right away due to the vertical torque applied by...
  43. WannabeNewton

    Thomas Precession references

    Hello! I was wondering if anyone knew of any good references (texts or whatever) to learn about the Thomas Precession. None of the current textbooks I own talk about it (maybe there is a chapter on it in Wald? I can't seem to find anything). In particular, I am dealing with a calculation...
  44. B

    Gyroscope Precession Explained: Simple Explanation

    I wanted to know if someone could explain how gyroscopic precession works. Preferably in normal physics terms and in laymens terms. Thanks :)
  45. R

    Magnetic field seen by electron in thomas precession

    According to Larmor's theorem, the magnetic field seen by a rotating frame is changed. In a frame that rotates at the Larmor frequency, the magnetic field appears nonexistent. In the treatment of thomas precession, the magnetic field in the instantaneous resting frame (which is rotating to...
  46. A

    Can you give some examples of vector precession equation dS/dz=ΩxS?

    Hi All, I know that vector precession equations such as mdV/dt=qBxV (Newton's Second Law written for the magnetic part of the Lorentz force) exist. In the last equation magnetic field B=(B1,B2,B3) acts as an effective torque and the speed V=(V1,V2,V3) is the “pseudo-spin vector”. These...
  47. A

    Kinetic Energy in Classical treatment of Larmor Precession

    This question pertains to the classical treatment of Larmor precession.I don't know whether to put it in the Classical Physics forum or this so I am putting it here. In the treatment we assume that the potential energy of the dipole-magnetic field system remains constant because there is no...
  48. edguy99

    Electron precession and flip contridiction?

    In a Leonard Susskind video lecture at http://www.youtube.com/watch?v=VtBRKw1Ab7E&feature=relmfu at 8:30 minutes he talks about an electron entering a strong magnetic field will precess, in fact does a demo of the precession with a stick. He states that the precession will end with radiated...
  49. H

    Larmor precession pi/2 out of phase

    Homework Statement I was going over the solution where it says \s_x, s_y are out of phase by pi/2. They first wrote equation of motion for \s_x, s_y and then did something to the matrix and now the have equation of motion for \s_+, s_- They rewrite \s_x, s_y in terms of \s_+, s_- to see that...
  50. amylase

    Phase-Locking Proton Precession with 90° RF at Lamour Frequency

    As title. Thank you. In the context of MRI, why/how does applying 90 degree radiofrequency at Lamour frequency put proton precessions into phase? I understand 90 degree RF minimises net magnetic moment, such that there is least difference between number of protons in parallel (with...
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