
A nice puzzle that you can easily setup yourself with a candle and a few bits and bobs.
Any ideas?
( , Sat 12 Jan 2013, 11:49, Reply)

Actually, if you light the third end of the candle then it opens a wormhole. It's just generally frowned upon in the Physics community.
( , Sat 12 Jan 2013, 12:00, Reply)

( , Sat 12 Jan 2013, 12:16, Reply)

( , Sat 12 Jan 2013, 15:50, Reply)

As it drips off one end, the weight reduces tipping the balance and that jolt causes the other end to drip, ad infinitum.
OR SUMTIN.
( , Sat 12 Jan 2013, 12:05, Reply)

It's acting as a mass balance. You can see the amplitude of oscillation jump as the wax drips off the low end. This loss of mass moves the centre of mass above the pivot and therefore accelerating the rotation. The oscillation then decays away before the next drip.
Level balance is maintained as the heavier end will be lower on average, therefore experiencing a higher melting rate.
( , Sat 12 Jan 2013, 12:56, Reply)

[edit] The wobbles are caused by the wax dripping off.
( , Sat 12 Jan 2013, 12:10, Reply)

For the sake of your well being I seriously hope that your exrement is not like plasma.
( , Sat 12 Jan 2013, 12:34, Reply)

My first explanation would go something like this:
The change in mass caused by wax melting off the ends is what causes the candle to oscillate, and it is the rate at which the wax melts from either end which limits the size/speed of the oscillations.
The lower end will lose wax more rapidly than the higher end, as it is exposed to more flame, thus shifting the weight to the other side of the pivot point, i.e., the higher end.
( , Sat 12 Jan 2013, 12:16, Reply)

Not for the mild-mannered trick, but for how excited you get about the smoke and its shadow.
( , Sat 12 Jan 2013, 12:21, Reply)

since they'll never burn at precisely the same rate, you'll get a situation where one side (A) drops, and so the other (B) is heavier.
B will then cause the system to rotate (I'm guessing very slowly at first) but this will bring the flame in to closer proximity with the wax, causing B to drip and lose weight; A will then be heavier and the process repeats. This will build up over time to create the fairly large motion you see in the video.
Any other ideas?
Edit: So yeah, what everyone else has already said.
( , Sat 12 Jan 2013, 12:41, Reply)

I reckon that there *could* also be a second effect that would cause oscillation, to do with the change in air pressure above and below the candle created by the difference of cold and warm air. Hot air expands and so the bit of hot air above the candle would provide a *lower* pressure and therefore push less down on a given side of the candle than the cold air below it would push up.
If you imagine that somehow side A has dipped down a little into the cold air below it, it will (initially) now have colder air on both sides, whereas side B that has moved up a little will have moved into the hot air above it, and so will have warmer air below it. So overall I'd think that maybe this would cause a greater push UP on the displaced side A, than the push UP that you get on the displaced side B, and so the candle would correct itself, most likely overshooting the level-position and continuting this cycle.
I haven't really thought about it hard enough to decide if that's really an effect though (for example, whether you would expect it to cause the candle to continue to oscillate or to quickly settle down). Needs testing. It's a shame you can't get a candle to burn in a vacuum, as sucking the air out of the vicinity would be a good test!
If it is indeed a factor then I'd reckon it wouldn't be nearly as important as the loss of mass that you rightly suggest.
( , Sat 12 Jan 2013, 14:06, Reply)

hadn't considered it, I assume it would have some effect, but I'm guessing the flame would provide some pretty fast heating action to the air in the vicinity so I don't know how transient this effect would be each time it oscillates.
( , Sat 12 Jan 2013, 14:23, Reply)

...too early and the system hasn't reached equilibrium and is still looping round the B end, that magic moss will have grown all over your eggs!
Or something similarly prime like.
( , Fri 18 Jan 2013, 22:36, Reply)

If there were a change of pressure then, according to Boyle's Law, the operator would be overcome by an uncontrollable urge to yawn in order to equalise the pressure in his ears.
As this didn't happen I can't see how it ca be an atmospheric pressure thing.
( , Sat 19 Jan 2013, 5:32, Reply)

PS: regarding the loss of mass due to the wax melting, I think that an important factor is also that when side A tips down, this allows the wax to drip off the recess that the flame has hollowed out, whereas side B is held up and so wax collects in its recess. Thus B is heavier than A and so we get a rotation. And then the situation is reversed.
A bit like if you had two buckets on the edges being filled with water from a non-spillable source - they empty each time they get tipped down.
( , Sat 12 Jan 2013, 14:09, Reply)

And your excitement would make it the best video ever. ~clicks~
( , Sat 12 Jan 2013, 12:44, Reply)

which can only be expressed through the dancing of the candle?
( , Sat 12 Jan 2013, 13:08, Reply)

Though, strictly speaking, the candle is not dancing: the movement is caused by disturbances in the 4th dimensional hyper-cube controlled by the the lizard people/royal family from within the hollow earth.
( , Sat 12 Jan 2013, 13:18, Reply)

Jesus, let it go already.
3.bp.blogspot.com/-wJ9M7EeZT5s/UPCEuYwzuMI/AAAAAAAAawg/9kMS0qM2pgA/s1600/541982_4136319418422_1985362037_n.jpg
( , Sat 12 Jan 2013, 13:24, Reply)

Yeah, sorry 'bout that. Perhaps a bit less hippy though? Besides, double rainbows are pre-school. THIS is a 'rainbow'* worth getting excited about...
upload.wikimedia.org/wikipedia/commons/3/30/HALO-S_south_pole.jpg
*It's actually a number of optical effects that are created by ice crystals as opposed to raindrops and that are seen centered around the sun as opposed to on the opposite side of the sky from the sun. But still rainbow-esque.
( , Sat 12 Jan 2013, 13:32, Reply)

the wax drips off one end making the other end heavier which results in the oscillations.
( , Sat 12 Jan 2013, 13:18, Reply)

I can't believe none of you have realised this.
( , Sat 12 Jan 2013, 13:28, Reply)

what your saying is that a candle some where will get excited about it?
( , Sat 12 Jan 2013, 15:54, Reply)

Perhaps its like one of those ducks that appears to sip water? The weight is changing at each end and upsetting the equilibrium?
( , Fri 18 Jan 2013, 18:52, Reply)

It's just smoke!! Sod the wobbly candle.
( , Fri 18 Jan 2013, 19:59, Reply)

I vaguely remember Jon Miller on Jack Hargreaves TV show How! doing something like this and I couldn't remember how it worked out so it was really nice to see. One of his top tips was to make firelighters out of dried orange peel
( , Wed 23 Jan 2013, 22:53, Reply)