# Drinking bird (toy) physics **URL:** \ **Category:** Factual Questions\ **Created:** [January 1, 2014, 12:07am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601 "2014-01-01T00:07:32Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [January 1, 2014, 12:07am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/1 "2014-01-01T00:07:32Z")
Here is the toy in question ([Drinking bird - Wikipedia](http://en.m.wikipedia.org/wiki/Drinking_bird)) Given all the physical characteristics like toy dimensions, room temperature, fluid characteristics etc. what is (theta) as a function of time ? I am asking for the mathematical formulation (I have a fairly good idea of what theta will depend on). Assume theta is 0 when the toy is vertical. Bonus question : what’s the time interval between each dip of the beak ? ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [January 1, 2014, 12:14am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/2 "2014-01-01T00:14:11Z")
FYI - I am looking for the equations of motion. For example look at the equations of motion for an inverted pendulum here : [Inverted pendulum - Wikipedia](http://en.m.wikipedia.org/wiki/Inverted_pendulum) ---
**Author:** ![JBDivmstr](https://avatars.discourse-cdn.com/v4/letter/j/b4bc9f/32.png) [@JBDivmstr](https://boards.straightdope.com/u/JBDivmstr)\ **Post date:** [January 1, 2014, 5:22am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/3 "2014-01-01T05:22:53Z")
I may be wrong, but it sounds like someone needs ‘help with their homework’. 😛 ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [January 1, 2014, 5:42am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/4 "2014-01-01T05:42:39Z")
This is NOT a simple mechanics problem. You’ll need to model evaporative cooling, heat flow, thermal expansion, and fluid mechanics in addition to your inverted pendulum problem. Good luck with that! ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [January 1, 2014, 4:39pm UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/5 "2014-01-01T16:39:13Z")
Yeah - but most of the phenomenon have been modeled 50 years or more back. So there’s no models ? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [January 1, 2014, 5:19pm UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/6 "2014-01-01T17:19:21Z")
Of course there are models. And they all interact in a complicated fashion. You _could_ model it, with accurate models of all the effects. It would be far easier for you to buy one, set it up, video tape it, and then plot theta as a function of time. It will be a very complicated, non-periodic function. ETA: You could probably find videos on the web. Give that a try and see what you come up with. ---
**Author:** ![Anaglyph](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)\ **Post date:** [January 2, 2014, 8:00am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/7 "2014-01-02T08:00:08Z")
This Article seem to contain the answer to your questions: [J. Guemez et al. , Experiments with the drinking bird,Am. J. Phys., Vol. 71, No. 12, pp 1257-1263](http://nautilus.fis.uc.pt/personal/mfiolhais/artigosdid/did14.pdf) ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [January 2, 2014, 2:07pm UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/8 "2014-01-02T14:07:02Z")
Thank you **Anaglyph**. Superb!! that’s what I was looking for. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 3, 2014, 1:03am UTC](https://boards.straightdope.com/t/drinking-bird-toy-physics/677601/9 "2014-01-03T01:03:40Z")
> [@](#): > > Quoth **ZenBeam** : > > It will be a very complicated, non-periodic function. There will be non-periodic transients initially, but they’ll die out (probably exponentially) leaving a purely periodic motion in the long run.