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. A

    Precession and its everyday applications

    Consider a top spinning. From experience we know that it's harder to tip over if it's spinning. I believe that is due to precession but I'm not sure why. I can see when I draw torque and angular momentum vectors, that the angular momentum vector just gets "shifted" a little to the right (or...
  2. J

    Understanding Gyroscopic Precession

    Hi, I'm having some trouble understanding how this works. I'm trying to put the pieces together but I'm hoping people here can help me. Specifically I'm wondering about a gyroscope positioned so that its axis lies in the horizontal plane and one end sits on top of a rod. So far what I've got...
  3. C

    NMR Theory, Relaxation and Precession

    Hello everyone, I'm having a really confusing time trying to get my head around these concepts, so I will try to explain what I can... So, in proton NMR we have nuclei that can be in either spin-up or spin-down states. Nuclei align with an external magnetic field but precess. (This precession...
  4. D

    Precession Tilt Angle: Exploring Physics of Spinning Top

    Im trying to understand the physics of the precession of a spinning top. What determines the tilt angle (the angle the top is tilted off the vertical axis)?
  5. grav-universe

    Precession of Mercury: Understanding Direction & Newtonian Gravity

    I am having trouble understanding something about the precession of Mercury. The precession takes place in the same direction of motion as the orbit of the planet, so that the ellipse of the orbit becomes angled slightly more forward over time, right? In a gravity simulator, this amounts to an...
  6. V

    How to use S-metric to periastron precession of binary stars

    The Schwarzschild metric allows to calculate the precession of an elliptic orbit of a particle around a large central mass, provided the mass of the particle is much smaller than the central mass M. This condition is not met in the case of binary stars m1 and m2 revolving around each other...
  7. B

    How to calculate perihelion precession

    Let’s say that a space probe orbiting the Sun in an elliptical orbit prove would emit heat towards the motion direction., and hence causing resistance against motion. Let’s say it would happen only when it was moving from aphelion towards perihelion, - and that the motion resistance is 1E-9...
  8. O

    The angular speed of precession for a gyroscope is given by

    The angular speed of precession for a gyroscope is given by ω_{p} = T/ω_{g}. So that the rate of precession increases as the gyroscope, top, or wheel slows down. This agrees with observations of a top, which wobbles around very quickly as it slows down. If I hold a bicycle wheel in my...
  9. E

    Torque-Free Precession in Classical & Quantum Mechanics

    In classical mechanics, an asymmetric rotating object will generally precess. Expressed in the body-fixed normal system of the object, we have I_i \dot{\omega_i}=(\vec{L}\times \vec{\omega})_i where L_i=I_i\omega_i. Choosing a simple example where I_1=I_2, we obtain \dot{\omega_3}=0 and, for...
  10. S

    Anomalous Precession of Mercury's Orbit: Facts & Theories

    There is so much confusion regarding the anomalous precession of Mercury's orbit. Mercury's orbit precesses at 575 arc-secs a century. Classical mechanics accounts for all except the anomalous 43 arc-secs. General relativity (curved space-time) accounts for the 43 secs. There are other theories...
  11. O

    Precession at LOW angular velocity

    So I've been working on understanding precession better. I had a whole other thread where it was explained to me how a torque applied to an object with angular momentum can result in precession. But this is sort of a different question, so I'd like to start a new thread for it. In my physics...
  12. S

    Does anyone recognize this precession matrix?

    Anyone know who was the originator of the matrix in the jpg file?
  13. D

    Decoding Mercury's Anomalous Precession: Discovering Pre-GR Explanations | [url]

    Does anyone know if anybody had successfully explained mercury’s anomalous precession before GR? The reason I ask is that I recently ran across this paper online. It seems to easy to not have been done after SR but prior to GR. Link: [url]http://toe.sytes.net:65333/planetary%20precession.pdf
  14. B

    Understanding Precession, Nutation, and Spin in Rotating Objects

    Hi guys ! Im trying to get my head round precession, nutation and spin. Suppose I have a cylinder of height L, base radius R. Initially it is just spinning about its central axis (i.e. line joining cone tip to the centre of base). In this scenario, centripetal acceleration experienced by say...
  15. A

    Could you help to calculate precession analytically?

    Hello. I have a formula for gravitational acceleration http://www.part.lt/img/eb4c24f748f6e9a2797ed354bfbe6051663.png And I have tested it by numerical integration. It looks it gives perfect results. For example 0.104 arc seconds per revolution for the Mercury precession. But I have no an idea...
  16. L

    Spin dynamics and Larmor precession

    Homework Statement Consider an electron with spin, which should be in a homogenous magnetic field B=B0ez. This situation is described by the Hamiltonian of the shape \hat{H}=g\frac{\mu_B}{\hbar}\textbf{BS}. Consider now the time dependent state |\psi(t)> of the electron in spin space. The...
  17. R

    Larmor Precession and Force on a Magnetic Dipole

    Homework Statement I have two questions. Both involve derivations from textbooks, not end-of-the-chapter problems. The two textbooks are Quantum Mechanics by Griffiths, and A Modern Approach to Quantum Mechanics by John Townsend. My first question is about the discussion of Larmor...
  18. T

    Precession of a Rotating Wheel

    Homework Statement Hi. I have: A 3 kg bicycle wheel rotating at a 2484 rev/min angular velocity has its shaft supported on one side. 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...
  19. U

    What is the observed precession of Mercury?

    The precession of Mercury is presented as one of the threshold moments for general relativity. Are there any publicly available summaries of the classical anomaly? Most refer to a 1947 paper that uses an outdated reference frame. Clemence, G. M. (1947). "The Relativity Effect in Planetary...
  20. P

    Gyroscopes and the torque required for precession

    Homework Statement The Hubble Space Telescope is stabilized to within an angle of about 2 millionths of a degree by means of a series of gyroscopes that spin at 1.92×10^4 rpm. Although the structure of these gyroscopes is actually quite complex, we can model each of the gyroscopes as a...
  21. G

    Lamor precession and diamagnetism

    i have some troubles to understand the lamor precession properly and i need your help to correct my errors: so in order to get the lamor precession: afaik you need something that causes a magnetic moment, e.g. an electron with spin or angular momentum. then you need a homogenous magnetic field...
  22. E

    Gravity Probe B / precession question

    I've been reading up on gravity probe B and the results, but I have a question about precession in general - I've heard it said that since the gyroscopes are in free fall there is no classical precession to be expected. So then, what explanation was there for Earth's precession before...
  23. U

    Precession of the LRL Vector in SR

    This is a continuation of https://www.physicsforums.com/showthread.php?t=526249", now that my confusion on Thomas precession has been clarified and my root question has been shown to not stem from this effect. In classical mechanics for any inverse square force, \vec{F}=-\frac{C}{r^2}\hat{r}...
  24. U

    Exploring Thomas Precession Magnitude and Direction

    I have been reading about Thomas precession and have encountered many papers that appear to give conflicting accounts of its magnitude and direction. In particular I am considering the portion of the DeSitter precession that is accounted for by the Thomas precession. I have found values...
  25. stevmg

    Einstein's Explanation of Mercury's Precession

    Einstein used General Relativity to explain the aberrant precession of the planet mercury in its orbit around the Sun and was shown to be correct. What the dickens , in 10th grade English, does the "precession of mercury" mean?
  26. M

    What is retrograde planetary perihelion precession?

    I know what each word mean independently, I'm just confused as to what sort of motion is trying to be described as a whole.
  27. R

    Connection between precession and resonance frequencies?

    I'm brushing up on my knowledge behind the physics of NMR. Turns out there was a lot I had misconceptions about; I thought it was very similar to absorbance/transmittance spectroscopy. I read some material about it which threw that idea out the window. I'm now looking at a video that shows a...
  28. B

    Understanding the Relativity-Induced Precession of Mercury's Orbit

    Can someone explain the cause of the Precession of Mercury’s Orbit in a "language" so simple that my grandmother can understand it? I mean only the part (43 arc second) that is due to relativity.
  29. B

    The perihelion precession of Jupiter

    One complete orbit of perihelion precession of Earth takes about 100,000 years How long time take one complete orbit of the perihelion precession Jupiter ?
  30. L

    Perihelion precession of Mercury

    Hi, It's found it Carroll that r=\frac{L^2}{GM(1+e\cos{((1-\alpha)\phi)}} . He states that this means we've found that during each orbit the perihelion advances by \Delta\phi=2\pi\alpha, I'm not sure that I follow this. Perihelion is the min value of r, and thus should correspond to whenever...
  31. L

    Need help figuring out precession rate

    Hi. I am working on a little project involving precession and I'm having a hard time figuring this one out. I am sitting on a chair hold a spinning bycicle wheel in my arms. When I twist the wheel to the side I will start to spin. What governs how fast I will spin? What is the equation...
  32. N

    Confused by wikipedia on (torque-free) precession

    Hello, I quote http://en.wikipedia.org/wiki/Precession from the first paragraph from the first section ("Torque-free precession"): But isn't the matrix product L = Iωs relative to the moving frame (that's how we did it in our course anyway), meaning L and omega are indeed the vectors as...
  33. T

    Precession of a football in flight

    I'm interested in the change of orientation of a football as it travels through the air Really quickly, I'm going to define a reference frame as such: x-axis: from one touchdown to the other, and in this case, also the line from quarterback to receiver. y: along the turf from sideline to...
  34. A

    Spinning Bycle wheel on string (precession)

    Trying to analyze all the dynamics of gyroscopic type motion. Assume the Z axis is vertical (which the wheel precesses about) Have a spinning bicyle wheel, that is held up via string on one end, the biycle wheel begins to precess about the vertical axes via torque induced from gravity...
  35. GRB 080319B

    Origin of gyroscopic precession

    Is precession caused by uneven mass distribution in the gyroscope, or by an uneven supporting surface, causing a couple to form (i.e., normal force and gravitation force start to have non-zero cross products)? Is precession analogous to circular motion, the angular momentum vector is having its...
  36. G

    Two precession rates for a spinning top (forced precession)

    When you have a spinning top undergoing forced precession (due to the torque created by its weight trying to tip it), you seem to get two precession rates. Why? I get this result from using Euler's equations, specifically that the sum of moments tipping the top is (in the case of steady...
  37. Pengwuino

    Mercury precession with naive GR

    The problem is to calculate the precession of Mercury using a naive approach: {{d(\gamma m \vec v)} \over {dt}} = {-GmM \over {r^2}} So apparently a Lagrangian of the form - mc^2 \sqrt {c^2 - \dot r^2 - r^2 \dot \theta ^2 } - {{Gmm} \over r} gives us a Lagrangian that obeys the previous...
  38. N

    Precession of the Sun's rotation axis

    Hi all, As the sun is an oblate spheroid and is rotating, should not the axis of rotation be precessing, much like the Earth does? What is the axial tilt angle and what is the precession period in years? Also, what is the amplitude and period of the nutation? Are there are equations for...
  39. DocZaius

    Would a specific change in earth's rate of precession mean no seasons?

    This is not a homework question. This is the result of trying to think of a way to remove seasons. Imagine a case where the Earth's axial precession had a period of exactly one year (instead of about 26,000 years) and that such a precession was counter clockwise (matching the direction of the...
  40. N

    Geodetic precession and parallel transport

    Could anyone give me a descriptive picture on WHY geodetic precession occurs? I understand the equations from which it follows, so I can derive it algebraically, but I would like to get an intuitive feeling of why it occurs too. My problem is the following: parallel transport of vectors along...
  41. TrickyDicky

    Explaining Mercury's Precession: Understanding the Role of General Relativity

    When applying GR to calculate Mercury's precession, the result is 43 arcseconds which coincides with the part of observed precession unexplained by Newtonian theory . My question is: why the formula from GR gives precisely this unexpained 43 arcseconds and not the total observed precession of...
  42. A

    Derivation of Thomas Precession formula

    I am looking for a derivation of Thomas Precession formula in special relativity. can anybody please suggest any online source (or book) for this?
  43. C

    How Does Precession Keep a Spinning Bicycle Wheel Upright?

    I am trying to understand how a rotating bicycle wheel doesn't fall over when you hold it on one side of the axle . I read a thing and it says , the top of the wheel wants to go to the left and the bottom of the wheel want to go right but when the wheel rotates these forces appose because...
  44. Z

    Mercury Precession & GR Calculation Impact

    When calculation GR, the component due to other planets is removed. In that calculation outer planets are assumed to be rings of mass and the effect of that mass is seen to have an effect on mercury precession ...
  45. Amith2006

    Why does a bicycle wheel precess when suspended from a string?

    Almost everything is clear to me as far as the reason for the precession of a bicycle wheel suspended by a string from a rigid support is concerned. But I don't understand one thing about it. There are 2 forces acting on the system- one is the downward force of gravity at the center of mass of...
  46. P

    Gyroscope Precession - Cause? - From Feynman

    I ran a search for gyroscopes looking for a definitive solution to the "What causes Precession?" and found no good clear answers. I think the Feynman lectures come close to the solution and followed that thought process, all the pieces point to the solution, I had to put my theory to the test on...
  47. G

    Derivation of Earth's Precession: Sun's Torque & Causes

    Hi, anybody knows of a book/article/source of any kind where I could check an actual rigorous derivation of the Sun's torque acting upon Earth? There's a couple of things I don't fully comprehend, maybe someone here could help me. 1- Why is it that if Earth would be a perfect sphere there...
  48. S

    Thomas Precession in Curved Spacetime - Giroscope Motion

    Hi guys, Is there a Thomas precession for a motion along a geodesic line in a curved spacetime? If yes, consider a little giroscope moving along a circular orbit in the Schwarzschild metric. What is the precession after a full cycle?
  49. C

    Calculating Precession Rates in 4C and 4D

    In the following question: http://phstudy.technion.ac.il/~wn114101/hw/wn2010_hw12.pdf How Do I caculate the precession rate in 4C? And also in 4D?
  50. B

    Mercury's Orbital Precession Anomaly

    The perihelion of Mercury precesses by 5600 arc-seconds per century, which is 43 arc-seconds per century more than Newtonian physics alone would predict Albert Einstein proposed a second-order correction to Mercury's orbit, based on his general theory of relativity. Which equation had...
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