22 February 2011

The Drinking Bird – Scientific Toy for the Ages

He looks a little ridiculous, a fuzzy headed bird with a top hat and a big bottom.  Yet in the 55 years since it was patented generations of children (not to mention those who refer to themselves as grownups) have laughed at his bobbling, dipping and nodding.  Yet behind the chortles and chuckles there is some serious science – this drinking bird seems to violate the laws of physics.

Seeming to do something and doing something are, of course, entirely different things and the drinking bird, also known as the dipping, dippy or even bobble bird is not, as some have suggested, a perpetual motion machine.  The bird ducks, takes a sip of water and bobs right back upright, rocking gently.  However, instead of becoming still the rocking becomes progressively wilder until he dips down and takes another drink.  This seems to go on and on – perpetually as it were. So what exactly is going on here?

The intervention of feline saboteurs aside, as with almost any invention of genius, the design of the dipping bird is deceptively simple. Basically the dipping bird is a glass tube and at each end there is a bulb, it’s as uncomplicated as that.  You can tell the top from the bottom easily.  The tube does not extend in to the top bulb but goes almost completely inside the lower bulb.

All the air is removed from the device when it is manufactured so the space inside is crammed with vapor, evaporated from the liquid, usually Methylene chloride.  A beak is placed on to the upper bulb and the head is covered with felt or a similar material.  Over the years variations on a theme have appeared but generally you get the beak, eyes, some tail feathers and that gloriously silly top hat.  The finishing touch to the contraption is the adjustable crosspiece upon which the glass shape pivots.

When the dipping bird seems to contradict the laws of physics it is in fact obeying them but the almost tromp l’oeil effect is what attracts us to it.  Perpetual motion machines do not (yet?) exist because in order to do so they would have to break the second law of thermodynamics.  The law insists that that the entropy of an isolated macroscopic system never decreases – to put it simply, you can’t break even.

One can only wonder if the inventor of the dipping bird, Miles V Sullivan broke even from his invention.  The idea began years before the patent and originally, as you might suspect, it had nothing to do with the bird.  Sullivan was an inventor-scientist at Bell Labs but as a young man he enjoyed evenings out.

It wasn’t the music or the lights but the bubbles in the tube at the sides of a juke box that grabbed his attention (see left, image credit Dawn Perry).  He noticed that the energy wasn’t going anywhere and the inventor determined that something could be done with them.  What he wanted to do was to harness motion- the idea of the bird came along later to make it more entertaining.  Of course, while it is simply for fun it is the science behind it which makes it work.

The contraption is what is known as a heat engine.     This is something that can be built when there are temperature differences that create energy.  To start the bobbing the head of the bird must be unceremoniously dunked in water.  The bottom bulb is room temperature.  The heat there raises the vapor pressure of the liquid inside to a higher degree than it is up in the head.

The liquid inevitably rises, making it top heavy – then it tips.  When it dips in to the water the temperature drops down.  It cools the vapour, the liquid drops back down to the bottom and the bird straightens up.  As long as there is water it can go – seemingly forever.  Time for a dipping bird face off.

Many assume that the liquid is colored water but it is Dichloromethane, an industrial paint stripper, degreaser and solvent. This organic compound is used since it has an accelerated rate of evaporation. Methylene chloride will irritate the skin and lungs but as long as the glass does not break, you are safe.  If it does spill, ventilate the room well and it will soon evaporate.

The bird, selling in its millions, ended up out of Sullivan’s hands.  He was in it simply for the fun – but he was at least named inventor of the year in 1979.  For a toy, however, it displays several physical laws and is a great tool with which to teach children something about chemistry and physics.

Among the laws it exhibits are the combined gas law, the ideal gas law and Maxwell-Bolztmann distribution, which is perhaps the most interesting.  It shows that molecules in a given space can vary in energy level and so can exist in more than one phase at a single temperature – in other words that they can be liquid or gas at the same temperature.

It also demonstrates enthalpy of vaporization, which shows that substances can give off or absorb heat when they undergo Maxwell-Bolztmann distribution.  Additionally, the dipping bird also shows torque, which the tendency of a force to rotate an object about an axis, not to mention center of mass, the position of the center of mass is fixed in relation to the body.

All in all, for a toy – it’s pretty clever.  It must be right up there in the pantheon of best toys of all time. Admit it, you want one – again.

On a final note, here at Kuriositas we would normally be the first to encourage the don’t dream it, be it mentality.  However, any maxim, those valuable principles that an individual uses to make decisions, can be taken to extremes.  In this case we think we might stick to don’t dream it, buy it instead!