Talk:Precession

Physics - first sentence

Precession is due to the fact that the resultant of the angular velocity of rotation and the angular velocity produced by the torque is an angular velocity about a line which makes an angle with the permanent rotation axis, and this angle lies in a plane at right angles to the plane of the couple producing the torque.

This sentence is quite confusing to me (and I believe many others). Could someone try to clarify it a bit? After reading it over several times and trying to think it through, I still don't believe that I have an adequate understanding to reword it myself.

I'd like to also make a nice diagram (like the one I made for Vortex ring), but first I've got to figure out the actual physical concept... ✈ James C. 05:48, 2004 Aug 22 (UTC)

Physics - first sentence revisited

Precession is an angular velocity produced by the resultant of the angular velocity of the rotating mass and the angular velocity generated by the torque. The axis of Precession lies at right angles to the permanent rotation axis (axis of the rotating mass) and the rotation axis resulting from the torque.

That is how I understand Precession. Is that correct?

The equation is also confusing me. Let me explain with an example; in a video at http://science.howstuffworks.com/gyroscope1.htm , I saw a bicycle wheel tied via one end of its axle to a string which was itself tied to the ceiling. Some person was holding the bicyle wheel such that the axle was horizontal (bicycle axle and string make a 90 degree angle), proceeds to spin the tire and let go.

Had the wheel not been spinning or spinning very slowly, intuition says the bicyle wheel would rotate such that the axle and string become parallel. However, because the bicyle wheel was rotating itself, instead of rotating such that axle and string align, the bicycle wheel instead begins to rotate about the string, axle remaining horizontal.

Back to the equation:

$T_{p}={\frac {4\pi ^{2}I_{s}}{QT_{s}}}$

In which I_s is the moment of inertia, T_s is the period of spin about the spin axis, and Q is the torque.

T_s is a measure of time defining a set rotation, say 360 degrees. Q is the Torque created by gravity pulling on the mass of the tire (approx mid axle) against the string (tied at one end of the axle).

Now, because of where T_s is located in the equation, keeping all other variables constant, increasing the duration of one 360 degree rotation decreases the duration of the precession spin. IE the precession spins faster about the string as the bicycle tire spins slower about its axle. That just doesn't make sense.

Where am I going wrong?

One way of interpreting that situation is to bear in mind that the faster the rate of rotation, the larger the angular momentum. The larger the angular momentum the smaller the response to a torque that is applied. If I hazard a guess I'd say that if the torque is increased proportional to the increase in angular momentum then the rate of precession remains the same. --Cleon Teunissen | Talk 22:50, 10 Mar 2005 (UTC)

Precession and Children of the Stones

The series Children of the Stones involves in part the prehistoric alignment of a stone circle with a black hole. The story is set in the present (well, 1977, though the series has not dated) - surely precession would have caused there to be a disparity of direction (for want of a better term)?

If this page can do no better than to define precession in the first paragraph in terms of Euler Angles....

Jeez, what is the point of this page if it cannot define precession without referring to Euler Angles?

This is yet another wiki page meant to serve wiki editors getting their phds then to serve any actual humans looking for an explanation.

I'd rate this page a D in terms of helpfulness, and yes, that actually is higher than the rating I give to most wiki pages. 107.3.134.101 (talk) 21:29, 10 September 2022 (UTC)