Huygens' Clock Puzzle Solved

PhotoGuy writes "Okay, I haven't heard of this puzzle either until now, but it sounds like a fascinating phenomenon. According to this article:Huygens had two clocks side by side and he found that even when they began out of sync, they soon got into a rhythm where the pendulum on one moved as if it were a mirror image of the other.The article is pretty light on the explanation, noting only the conditions required (small relative mass of the pendulums [pendula?], relatively close speed of the clocks), and not really addressing the physics behind it. " There's a great site at Georgia Tech that explains the puzzle in more detail.

Comments

the article from wired about it

[itsnotme]

The GA tech column had an link to a picture of the wired article about it, I dug into Wired and found the text so it's more readable.. the link is: http://www.wired.com/wired/archive/9.03/eword.html ?pg=6

A better article...

[LordSah]

http://www.sciencenews.org/20001007/mathtrek.asp

Re:Periods

[ender81b]

That's called the Harem effect (or something like that). Basically you get any number of women, greater than 1, put them into close contact with each other and they all have their period at the (nearly) same time. Well documented phenomeon(sp?).

Harem, because a man could impregnate his entire Harem in a single day since they all became fertile on the same day.

Re:trivial?

[Hammerself]

In this (Huygens') case they start out in phase and move to 180 degrees out of phase.

Re:Periods

[Tha_Zanthrax]

What you're explaining is pretty common for women who spend a lot of time together. It's being caused by pheromones and why it happens... I forget.

Unless someone discovers clocks with pheremones these things aren't related.

No similarity

[Jetson]

The synchronizing of the female reproductive cycle is thought to be the result of pheremones. I suppose it's some prehistoric competitive thing that ensures the male never has to resort to the less dominant females.

That has nothing to do with pendulums. The key point of the phenomenon is that the two clocks must be on a base which is wobbly enough to transmit the "equal and opposite reaction" of the pendulum from one clock to the other while being strong enough to prevent the pendulum from swinging the clock.

Phenomonon observed directly

[paulwomack]

This whacky guy observed and measured the effect in his own clocks.

BugBear

Massive Huygens entrainment.

[Richard Kirk]

I one had a posting from an old steam train worker on Africa somwhere. They used to have pairs of back-to-back steam engines for pulling heavy trains. The drive wheels used to have a random scatter in the diameter, and people in the engine shed used to try and match up sets of driving wheels with the same diameter, because that made the enginges 'run more smoothly'. From his account, it seems that on long, straight sections of track, the two engines would lock into step, but only if the wheels were a near match on both engines.

You get it with piano strings too. Where two or more are tuned to the same note. The delta in tuning has an important on the sustain-decay profile of the notes.

Huygens figured out the general principle. If you have two things that are matched in frequency, and capable of influencing each other, then any influence, however tiny, will eventually drag them into some preferred phase relationship. If there is some difference in frequency, then this may destroy the coupling effect, if it is too small. You get it with piano strings too. Where two or more are tuned to the same note. The delta in tuning has an important on the sustain-decay profile of the notes. Arguing that entrainment must exist to some degree between two clocks is easy. Showing exactly what causes it is a lot harder. That is what the recent paper was about.

Re:Massive Huygens entrainment.

[gwernol]

I one had a posting from an old steam train worker on Africa somwhere. They used to have pairs of back-to-back steam engines for pulling heavy trains. The drive wheels used to have a random scatter in the diameter, and people in the engine shed used to try and match up sets of driving wheels with the same diameter, because that made the enginges 'run more smoothly'. From his account, it seems that on long, straight sections of track, the two engines would lock into step, but only if the wheels were a near match on both engines.

This is a relatively well-known phenomenon on steam railways. A good example if the Ffestiniog Railway in Wales which runs the (now) unique Fairlie double engines. These locomotives have two boilers and two mechanically separate engine units that swively independently on pivots under the main frames. You can see this on the photograph here. Effectively these are two back-to-back locomotives joined together.

The two engine units will synchronize when the locomotives run on relatively straight sections of track. Again the prevailing theory is that the synchronization occurs because of vibrations transmitted through the main frame.

The Ffestiniog also has a pair of near-identical Hunslet locomotives that are sometimes run double-headed. These will also synchronize to each other, again presumably synching through the vibrations transmitted between them. Its interesting that the locos have to be of similar types for the synchronization to occur: it doesn't happen when dissimilar locos double-head. Going back to clocks, I would guess that the phenomenon does not happen when the pendulum lengths or other characteristics of the clocks are different.

Re:Mainly luck?

[jstott]

t seems that the main reason this happens is that the synchronus movement causes less vibration in the system as a whole, and therefore conserves more energy. A path-of-least-resistance sort of thing.

Perhaps there's a physics major out there who could explain better...

That's basically it. The proper term is mode-locking. It's also the reason why one side of the moon always faces the earth and why there's a 3/2 ratio in the time of the orbits of Uranus to Neptune. You can also make some really cool high-power lasers if you mode-lock the period to the cavity length (Ti:Sapphires are the most common).

-JS

Re:Periods

[chad_r]

Is it true the menstrual cycles of women living together tend to synchronize?

... This amazing phenomenon was first described in 1971 by researcher Martha McClintock, now with the University of Chicago. Having asked around a bit, I'd say it's common knowledge among women, but I'll bet not one male in 50 has ever heard of it. Women do have their little secrets....

...Later research has suggested that synchrony is caused by some sort of scent cue, or pheromone.

Scientists at the Sonoma State Hospital Brain Behavior Research Center in California identified several women who were believed to be menstrual pacesetters--they made other women conform to their cycles.

The scientists placed cotton pads under the dominant women's arms for a day, and then wiped the pads on the upper lips of five female subjects three times a week. (One wonders how much the subjects got paid for this.)

Within five months, four of the recipients were menstruating at the same time as their donors.

Interestingly, men also have an effect on women's menstrual cycles--and not just because they make women pregnant. Women who associate with males frequently find that their periods become shorter and more regular....