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.

View More On Wikipedia.org
Recent contents Top users
  1. Bobs

    Quantum version of Larmor precession

    Homework Statement Homework Equations I didn't get what this actually means. The Attempt at a Solution I'm not sure whether it is correct. Could you take a look? Regards!
  2. P

    I Free Precession animation - body frame to space frame

    I'm creating an animation of free precession of a cuboid in GeoGebra. The axis of rotation is not one of the principal axes (but does go through center of mass). Since it's much easier to find the angular velocity and L in the body frame, I defined the e1, e2 and e3 axes (as opposed to the...
  3. G

    Why is the Gödel Universe Rotating

    Homework Statement Consider the Godel Metric in spherical coordinates as on page 6 here; ds^2=4a^2\left[-dt^2+dr^2+dz^2-(\sinh^{4}(r)-\sinh^{2}(r))d\phi^2+2\sqrt{2}\sinh^{2}(r)dt d\phi)\right] This is a solution to Einstein's Equations if we have ##a=\frac{1}{2\sqrt{2\pi\rho}}## and ##\Lambda...
  4. J

    Angular momentum direction for a spinning top

    Homework Statement Hi I'm having trouble with a question that's asking me to calculate the precession rate for a spinning top. The trouble that I'm having is that I don't understand how the angular momentum points along the axis of the spinning top (picture attached). When I use the formula...
  5. F

    I Lunar apsidal precession relative to equinox

    The period of the lunar apsidal precession is about 8.8506 years measured against fixed starts. How can I accurately convert this to the period between alignments with spring equinox? Thanks.
  6. SchroedingersLion

    Precession - why does the rotational axis change as L changes?

    Hi guys, while going through rotational energy levels of molecules, I found myself struggling with a very basic concept. The concept of precession, in terms of a torque induced rotation of the rotational axis of a spinning rigid body. Take a glance at the Wikipedia figure...
  7. riveay

    Euler angles in torque free precession of a symmetric top

    Is calculating the Euler angles analitically possible? I am trying to obtain the angles to transform the body-fixed reference frame to the inertial reference frame. I can get them without problems with numerical methods. But I would to validate them analitically, if possible. I followed the...
  8. L

    Gyroscope precession compensation questions

    Hello I was watching some videos about gyroscopes and inertial guidance. In one of the videos lecturer said that rotating gyroscope set in one direction on gimbal will be pointing one direction and stay like this virtually forever, so we can use it for guidance system. However I read more...
  9. JTC

    I Direct vs. Retrograde Precession

    (This is not about the motion of the planets.) If one takes a body in space (not outer space, necessarily) with only central forces, it may exhibit one of two types of precession: direct or retrograde. If the body is flat, the precession is retrograde: the spin and precession rates have...
  10. A

    Precession of Rotating Rigid Body from Two Different Frames

    Homework Statement A) Use Euler's equations to solve for the precession rate of a rapidly spinning gyroscope precessing uniformly (no nutation). Use I3 for the moment along the z axis along the axle. Beginning with Euler's equations, derive the coupled equations: ## \dot ω_1 + Ω ω_2 = \frac...
  11. P

    I Help with formula to calculate the precession rate change

    First time caller, I'm a newb so go easy on me. So I was trying to work through a calculation to figure out the precession rate variation in terms of the Precession of the Equinox. I came across the following formula from...
  12. S

    A Perihelion Precession in GR with Robertson Expansion

    In his book Gravitation and cosmology, Weinberg derives the perihelion precession of Mercury in the Robertson expansion. The final formula is \Delta\phi =\frac{6\pi M G}{L} \frac{2+2\gamma-\beta}{3} The second term is one for GR (β=γ=1). I have two questions regarding this formula: 1. The...
  13. G

    I Mercury's precession due to other planets

    Hi. I'm interested in how physicists in the mid-19th century such as Urbain Le Verrier were able to compute the gravitational influences of the other planets on the apsidal precession of Mercury's orbit, finding that they can only explain about 531" (per century!), not the observed 574". This...
  14. N

    I Kleppner & Kolenkow derivation error in free precession?

    Hi all. I ended up to this section in K&K (2nd edition, but with 1st is the same) when they derive the wobbling motion of a simple body in torque-free precession. [see the attached file] Equations 8.23 and 8.24 are integrated into 8.25[a|b], but I think signs are wrong. Shouldn't be negative...
  15. GhostLoveScore

    I Precession of a spinning wheel

    This is the experiment I am a bit confused about this part: There is a torque on the wheel from its own weight. That's the τ on the picture. In this perspective, τ points at the bottom of the page. I understand that that torque changes angular momentum of the wheel and the wheel starts...
  16. E

    B Gyroscopic precession force diagram

    Hi, I've been learning about gyroscopic precession recently and I feel like I get it. I understand that when the flywheel of a gyroscope is spinning its angular moment plus the angular moment created by the torque from the force of gravity makes it turn. But I were thinking about the forces in a...
  17. T

    A Understanding spin precession in a magnetic field

    I have some trouble understanding the concept of spin precession in an external field from a quantum mechanics viewpoint. Hopefully someone will be willing to enlighten me. Consider a single spin ½ particle. In the absence of an external field, the projection of the spin angular momentum on...
  18. T

    I Gyroscopic Precession: Understanding the Physics

    I was watching this and I get it that when you rotate the wheel, the torque due to its weight will cause it to revolve parallel to the ground instead of perpendicular to the ground. I know that the faster you spin the wheel, the less likely the lever from the wheel to the pivot will be slanted...
  19. U

    I Mercury Precession and the Hypothetical Oblate Sun Model

    I have a student who thinks he is smarter than me. When we calculate the precession the classical way we also account for the supposed oblate sun. If we model sun's oblateness by splitting the mass of the Sun into 2 masses and separate them by distance s, then the acceleration we get on point...
  20. Physics Dad

    Calculating Torque for Gyroscopes to Precess in Hubble Telescope

    Question 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 1.92×104 rpm . Although the structure of these gyroscopes is actually quite complex, we can model each of the gyroscopes as a thin-walled...
  21. E

    I Moment and the Larmor precession

    Hi, In the Larmor precession, we tend to define the magnetic moment as the current multiplied by the surface (for an electron rotating around a nucleus), sometimes this moment is defined (generally) as the sum of the vectoriel products of half of the position vector and the charge times the...
  22. Twigg

    I Where Does Larmor Precession Occur?

    I have been doing a lot of exercises out of Griffiths lately, and one thing I spent a lot of time thinking about was Larmor precession. It's a fun thing to work out, but where does it actually happen? I'm having a hard time to see where it would apply. The first condition for Larmor precession...
  23. B

    Insights Orbital Precession in the Schwarzschild and Kerr Metrics - Comments

    Bill_K submitted a new PF Insights post Orbital Precession in the Schwarzschild and Kerr Metrics Continue reading the Original PF Insights Post.
  24. N

    I GR & Mercury Precession: Explaining the Diff.

    Im curious what is it about space-time or Einsteins field equations which explains Mercurys precession correct while Newton's formula doesn't? So exactly what difference causes GR to explain it that Newton could not?
  25. B

    Insights Precession in Special and General Relativity - Comments

    Bill_K submitted a new PF Insights post https://www.physicsforums.com/insights/precession-special-general-relativity/ https://www.physicsforums.com/insights/precession-special-general-relativity/
  26. Tazerfish

    I Can every shape precess like a top (toy)?

    The main question is in the title. 1.I have wondered if a regular pencil would precess and rotate stable for multiple seconds if spun fast enough. [Coins, plates, bowls and similarly shaped objects can rotate in a stable way for extended periods of time. And a lot of other household objects...
  27. S

    A Relativistic orbital precession in practice

    I'm interested how was measured the famous Mercury's precession: 43'' / cy. How it has been measured? where is the angle 43'' - in this image: http://en.wikibooks.org/wiki/Astrodynamics/Classical_Orbit_Elements The preccesion is about the periapse, so it's defined wrt the node: therefore...
  28. S

    Proof derivative of a vector following precession motion

    I do not get some points of this proof about the time derivative of a unit vector $\hat{u}$ (costant magnitude) which is following a precession motion. The picture is the following. I want to prove that $$\frac{d\hat{u}}{dt}=\vec{\Omega}\wedge \hat{u}.$$ I'm ok with almost all the proof except...
  29. B

    Clarification about Earth's Precession

    I haven't a textbook where I can study Earth Precession and I'm not sure to have correctly understood... Could you tell me if I do mistakes? I consider two points P and Q on the equatorial bulge. The torques of the gravitation forces between P-sun and Q-sun (calculated wrt the Earth center) are...
  30. H

    Deriving Precession from First Principles

    I'm trying to figure out the effect of a force applied to a rotating body in 4+1 dimensions. A good place to start would be deriving the effect of forces in 3+1 dimensions. I have been looking around the Internet and even went to the local community college and checked out texts in the library...
  31. G

    Precession, Weight & Conservation of Angular Momentum

    Many of you might have seen veritasium's video on the "Anti-gravity wheel". Through one of the comments, I was introduced to the idea that the reason the apparatus is so easy to lift is because the energy to do so comes from the spin of the wheel, i.e. its rotation slows down as it is lifted and...
  32. G

    Translational approach to precession

    Hi. I'm trying to take a purely translational approach to precession (i.e. not using angular momentum and torque). I'm looking at a gyroscope that consists of four point masses on a cross and at a moment in time when one mass is at the topmost point (see sketch). I'm assuming a virtual...
  33. F

    A What is the cause of lunar nodal and apsidal precession?

    Over the last year or so I've been doing quite a bit of reading trying to find out what is actually causing lunar nodal precession. There seems to be a lot of handwaving but no definitive answer, which I find rather odd. Maybe I've just not found the right source. Google seems obsessed with...
  34. G

    What if I force a spinning wheel not to precede?

    Hi, If we apply a torque to a spinning wheel such that the torque vector lies in the plane of the wheel, it will precede around the axis perpendicular to the angular momentum and the torque. What happens if the wheel is mounted such that rotation around this axis is absolutely impossible and...
  35. H

    Does Jupiter have precession of the equinoxes?

    I would think that precession of the equinoxes occurs only if the planet is at least partially rigid. Since Jupiter is gas and liquid, it would not experience precession of the equinoxes. Is this right?
  36. H

    Coriolus effect, precession in 4+1D?

    Here is a derivation of the Coriolus effect on an imaginary 4+1D planet. http://hi.gher.space/forum/viewtopic.php?f=27&t=2106 It seems wrong to me. I think that the planet is rigid, so the latitude of a point on the surface, ϑ, is a constant. It's derivative will always be zero. The first...
  37. nmsurobert

    Precession of 1/2 spin particle

    Homework Statement A beam of spin 1/2 particles with speed v passes through a series of SGz devices. The first SGz device transmits particles with Sz = ħ/2 and filters out particles with Sz=-ħ/2. The second SGz device transmits particles with Sz=-ħ/2 and filters out particles of Sz=ħ/2...
  38. I

    Earth's orbit & precession affected by Venus & Jupiter?

    I watched a program that said that some of Earth's past climate change was due to variations in Earth's orbit and precession due to the the gravitational perturbations caused by Venus and Jupiter. Why would that be so? I know that the orbits of the planets are eliiptical generally and they...
  39. jaketsi

    How Does Angular Momentum Affect the Behavior of a Rotating Drone System?

    Hi folks!First of all, English is not my native language so I hope there is not much misleading spelling mistakes, discrepancies and inaccuracy. I’m currently working with a hobby-project of a flying drone/UAV with two adjustable angled rotors. I’m able to make it fly more or less in a way it...
  40. J

    Precession of angular momentum in vector model

    Hey everyone, I just made an account because I have a problem concerning angular momentum and precession. In the picture below you see the vectors l1 and l2 that make up total orbital angular momentum L precess around L. I can get my head around why that is the case. The same for s1 and s2...
  41. DeathbyGreen

    Larmor precession and magnetic ordering

    Homework Statement When we speak about Larmor precession we refer to atomic magnetic moments precessing in a magnetic field. In ordered magnets, such as ferromagnets, I never hear about larmor precession anymore. Are the magnetic moments frozen due to interactions with the surrounding crystal...
  42. G

    Gyroscopeic Precession: How Does Angular Momentum Arise?

    Once the gyroscope starts to spin about the pivot it acquires an upward angular momentum. But since it did not have any angular momentum in this direction before, and the only torque is due to the gravitational force, how does this new angular momentum suddenly arise. Isn't this a violation of...
  43. J-dizzal

    How Does the Angle of Tilt Affect Gyroscope Precession Rate?

    Homework Statement A top spins at 33 rev/s about an axis that makes an angle of 26° with the vertical. The mass of the top is 0.47 kg, its rotational inertia about its central axis is 5.0 x 10-4 kg·m2, and its center of mass is 3.1 cm from the pivot point. The spin is clockwise from an overhead...
  44. 24forChromium

    When a gyroscope precesses, what is pushing it along?

    This is the kind of gyroscope that I am talking about: Where did the kinetic energy of precession come from? The gyroscope's spinning angular inertia? If so, how does it transfer into the precession? Is a torque applied horizontally (along the x-y plane) when the system is under the effect of...
  45. C

    Gyroscopic precession of a bicycle wheel

    Hello! I have recently been looking into the phenomenon of gyroscopic precession in my free time, and there is a scenario which I am not sure I have fully understood. Here it is: Imagine a bicycle wheel with a shaft running through it's center. The shaft is attached to a rope at one of it's...
  46. J

    Gyroscopic precession with dual counter rotation

    I watched an interesting video on YouTube by veratisirm where he had a meter long metal rod with a huge metal fly wheel on the end of it. Long story short he could barely lift the thing but under full spin he could just about swing the thing like a sword. the only thing was the precession wanted...
  47. WannabeNewton

    Calculating Differential Precession of Gyroscopes Due to Gravitational Waves

    To motivate the question, Andy Strominger recently put out a paper on calculating the Sagnac shift of counterrotating beams due to the angular momentum flux of a passing gravitational wave. See here: http://arxiv.org/abs/1502.06120. But consider now two nearby freely falling gyroscopes...
  48. S

    Gyroscopic Precession: Find Speed & Frequency of Nutation

    Hello, I am doing a project on a Gyroscopic Briefcase. What i want to know is that, if i add some additional mass to the rotating gyroscope ( which is in preceession ) what would be the result in the precession of gyroscope? Is there any numerical way to find the final result (i.e. speed...
  49. TCups

    Precession of an air rifle pellet in flight

    Unlike firearm projectiles, air rifle pellets have evolved to a generally typical diabolo configuration. For reference, see: http://www.photosbykev.com/wordpress/2009/01/20/air-rifle-pellet-database/ The initial shape was described as like that of a badminton shuttlecock, and "skirt" at the...
  50. naho

    How to calculate the precession

    This is the Anti gravity wheel video from Veritassium. I have a similar problem to calculate the forces on arm. How can I calculate the precession force pushing the arm vertically ? Lets assume that the angles between shaft and arm is 90° the angles between shaft and wheel is 90° The wheel...
Back
Top