Talk:Pendulum/Archive 2

Solidus overkill
Why are there so many solidi (/) in the example diagram and it's explanation? Just call it a (frictionless) pivot, cord, and bob. The article text can go into the details of the variety of feasible implementations, etc.. --Belg4mit 18:35, 28 May 2007 (UTC)

Other types of Pendulums/Pendula
In my youth I experimented with pendulums which had fulcrums/fulcra/points of rotation somewhere along the length of the rod rather than at the top end. In addition most had an additional bob above the fulcrum as well as below. Such pendulums can have a very long period of oscillation and still be quite short. I can't find these mentioned anywhere and I have no idea what they might be called ! Velela 18:18, 8 March 2007 (UTC).

I have seen some old school metronome that have that use pendulums of this sort. I am not sure of myself but I beleive that many of them have wind up springs as well to keep the motion going similar to a clock.

Also I think some of the things listed as pendulums dont really qualify. Not every swinging object is a pendulum. A swinging object becomes a pendulum when it's rythmic swinging makes it stand out.Marcusyoder 23:43, 14 April 2007 (UTC)


 * "makes it stand out" what kind of physics standard is that? A pendulum is any (free) swinging mass, period. Dangling a pocket watch by its fob as a hypnotist might is using it as a pendulum. --Belg4mit 18:43, 28 May 2007 (UTC)


 * I came to the talk page because I didn't feel this page does enough to define the allowable dynamics of a pendulum system. Is a Tetherball a pendulum?  In a frictionless environment where the ball is tracking a perfect circle (what is the equilibrium point it "oscillates" around?)  MaxEnt 19:29, 26 July 2007 (UTC)
 * This type of pendulum is mentioned in the article as a conical pendulum, although it's easy to miss. The article could probably use more illustrations. -- Chetvorno TALK 13:10, 7 December 2007 (UTC)


 * The solid rod is a compound pendulum? Do we not have an article on this?  We do have Kater's pendulum. ''  d b f i r s   08:58, 12 April 2008 (UTC)

Revert 5 Nov 2007
If not vandalism this was almost pure Gibberish not English: A pendulum is an object it will go right down, when velocity is being zero--SilasW 08:29, 5 November 2007 (UTC)

I believe the acceleration vector shown in the animation is incorrect.
The acceleration experienced by the pendulum mass is vertical and, for all practical purposes constant, as it is from the graviatational field in which the pendulum is immersed. —Preceding unsigned comment added by Jrufener (talk • contribs) 00:58, 28 December 2007 (UTC)


 * It would be if it was falling free. The pendulum rod forces the mass to move in a circular arc. The acceleration is the vector sum of a component tangentially along the path toward the equilibrium position,  due to the changing velocity of the mass, and a component directed radially up toward the pivot due to the curvature of the path. -- Chetvorno TALK 19:57, 28 December 2007 (UTC)

$$Insert formula here$$

Driven Pendulum
Check out this site: http://monet.physik.unibas.ch/~elmer/pendulum/eqm1.htm

The equation seems to be slightly different.


 * The equation refers to the general case of oscillations with arbitrary amplitude. If the oscillations are small, sin x $$\simeq$$ x and we go back to the case discussed in the main article. I have added the solution for the general case --Tai89ch 19:36, 3 September 2007 (UTC)

Also, would someone explain the equations for a driven pendulum?

Did the pendulum originally define the meter?
The pendulum had a historical role in defining the meter unit of length. The 'seconds' pendulum, which has a period of 2 seconds, or 1 'beat' per second, is approximately 1 meter long. When the SI system of units was created in the 1790s, it was originally proposed that the meter be defined as the length of a pendulum that swings at 1 beat/second (see meter). This would make it easy for anyone with an accurate clock to recreate the meter standard. Although this definition lost out to a meridional one, pendulums were used by scientists of the era to measure length. This might be an interesting tidbit to add to the article, if someone can find a reference. --Chetvorno 22:32, 3 October 2007 (UTC)
 * See metre (History) for the reference.   D b f i r s   06:51, 8 May 2008 (UTC)
 * Thanks -- Chetvorno TALK 19:31, 27 June 2008 (UTC)

Pendulum Dowsing?
The section on religious practices is very weak. It mentions nothing of dowsing with pendulums at all. Perhaps someone could put in something about the use of pendulums in spiriutalism? 64.39.147.192 (talk) 04:15, 28 April 2008 (UTC)
 * I think these uses would be better recorded under dowsing and spiritualism.   D b f i r s   06:53, 8 May 2008 (UTC)
 * (later) Use mentioned in dowsing (but see "Possible explanations"). No mention in the article on Spiritualism.  Is it common to use a pendulum?    D b f i r s   06:59, 8 May 2008 (UTC)

Pendulums and The Cycloid
I can find nothing here on pendulums altered to follow a cycloidal arc. Could some information be added or a link provided?

pendulum
this is spo funy it makes me laugh hard hehehehehehehehe

pendulum c,/f o
this is spo funy it makes me laugh hard hehehehehehehehe PISS —Preceding unsigned comment added by 198.237.134.3 (talk) 20:52, 2 March 2009 (UTC)

pendulum c,/rf6ii6t6if o
this is spo funy it makes me laugh hard hehehehehehehehe —Preceding unsigned comment added by 207.190.176.254 (talk) 17:27, 26 February 2009 (UTC)

Baffling
Pendelums. In the third para I read: "The presence of g in the periodicity equation..."

The presence of what in the what?

I read below a lot of people talking mathematics. Has it got anything to do with the article it is supposed to be discussing?

150.203.224.165 (talk) 02:30, 23 January 2009 (UTC) - Pepper

Acceleration vector
Anon editor 134.121.110.201 removed the GIF, claiming that the acceleration vector was incorrect. I have restored the animation because I cannot see anything wrong with it. Can anyone else see a flaw?  D b f i r s   00:06, 27 February 2009 (UTC)


 * It looks correct to me. I think that editor mistook acceleration for force.  Glad you put it back. -- Chetvorno TALK 17:45, 18 March 2009 (UTC)


 * In the image http://upload.wikimedia.org/wikipedia/commons/2/21/Pendulum_animation.gif the acceleration vector seems to be messed up. In my opinion the acceleration vector can only be tangential to the circle of motion (likewise the overall force vector which is a superposition of the gravitational force and the force exerted by the string). For the overall force vector I got the following:
 * $$F=(\ -mg *\sin(\theta)*\cos(\theta) \, \ -mg*\sin^2 (\theta)\ )$$


 * with the positional vector being $$x=(\ l*\sin(\theta)\ ,\ -l*cos(\theta)\ ) $$


 * The dot product of the two yields 0 and thus the force vector (and also the acceleration vector F=ma) is perpendicular to the position vector. 94.79.180.77 (talk) 21:31, 18 November 2009 (UTC)


 * OK, I see. The above equation for F is only true for the stationary case. If the pendulum is in motion the centrifugal force accounts for the somewhat puzzling behavior seen in the animation. But it is correct. 94.79.180.77 (talk) 19:39, 19 November 2009 (UTC)
 * Yeah, the acceleration consists of two perpendicular components, a tangential component due to the linear acceleration that is maximum at the ends of the swing and zero at the center, and a radial centripetal component proportional to velocity that is zero at the ends and maximum at the center. -- Chetvorno TALK 20:21, 19 November 2009 (UTC)


 * ... there is no such thing as a 'centrifugal force'...
 * BravoNovemberGolf (talk) 12:28, 25 March 2011 (UTC)

Rewrite
Did an extensive rewrite of the article which addressed some of the above criticisms. I plan to add supporting citations to some of the later sections that don't have them. -- Chetvorno TALK 22:04, 3 March 2009 (UTC)
 * Congratulations on an impressive rewrite. We now have a much-improved article.    D b f i r s   08:15, 7 March 2009 (UTC)

Torture and execution
Is there any source for the 'torture and execution' section? The method is described in The Pit and the Pendulum (by Edgar Allen Poe I think), but is there any evidence it was ever really used? The mechanism to drop a pendulum with each swing would probably be unduly complex.

Atmospheric pressure
This is a nice article. I've been looking into the effects of atmospheric presssure quite carefully. I think it's wrong to say that air resistance has a negligible effect on the period. See http://www.trin.cam.ac.uk/clock/theory/pendulum.pdf where it is found that the reduction in amplitude due to drag causes the going to increase. For the Trinity College clock I'd expect buoyancy and added mass to cause -12 ms/day per mbar, but it's more like -8ms/day per mbar (recent low pressure makes this clear, see http://www.trin.cam.ac.uk/clock/viewlong.php?from=-30days&to=today&channel=going&channel2=pressure&type=xy&scale=auto ) It's hard to quantify the drag on the pendulum (though I think it's form drag, not viscous). My guess is that the drag effect on going is about 50% as big as the buoyancy+added mass effect, but in the opposite direction. While I'm at it, is this article an appropriate place to talk about this: http://www.trin.cam.ac.uk/clock/viewlong.php?from=03%2F05%2F2009&to=04%2F05%2F2009&channel=going&channel2=amp&type=xy&scale=auto which shows experimentally how the period of swing varies with amplitude - and how beautifully it agrees with the theory? —Preceding unsigned comment added by Hughhunt (talk • contribs) 22:54, 4 November 2009 (UTC)

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