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Physics of Drinking Bird...
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Many of us have seen a toy looking like a bird standing near a cup of water and dipping its nose in the water again and again, and doing this forever. The bird does not seem to stop drinking the water for days and months together! Where does the energy come from to keep swinging the bird? Is there any thing wrong in the understanding of the law of thermodynamics, which states that the energy can never be created nor be destryed; it only changes its forms” ? Are we getting something for free without any input?
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The answer is NO. We are not getting anything free. The only thing is that the input is invisible and difficult to get noticed at first glance.
Here is the explanation of how the swinging continues non-stop.
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First let us undestand the parts of the bird. The bird is made of glass.The body, which is a tube, takes the shape of the head on the top end. The lower end of the body, tube, is dipped into a spherical ball shaped end at the bottom. The liquid which you see inside is a chemcial having very low boiling point close to normal room temperatures. When I had made one such bird long back, I had used Ether which has a boiling point of 34 degrees Celcius. The head is covered with a felt which
becomes wet when dipped into water. The felt retains the water in it. The red
ether and the water outside does not come in contact in any way. The space
above the red liquid is all vacuum. It is created while filling the ether in
the body of the bird.
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When the air above the red liquid is removed by vacuum pump, it gets filled with gaseous vapor of ether. Now, to begin with, let us make the head of the bird wet by tilting the body over the cup and allow the felt on the head to soak some water. When the bird’s body is allowed to stay upright the following things happen. a) The water in the felt starts evaporating into the surrounding b) This makes the temperature of the vaour inside
the bird’s body to fall. This is same as what happends in case of earthen pots used in c) When the temperature falls below the boiling point of the ether, it suddenly chnages its form from gaseous state to liquid state. d) Liquid being more dense than the vapour, it requires very little space. e) The partial vacuum created inside the tube pulls the liquid from the bob upwards. f) This rising liquid disturbs the centre of gravity of the bird’s body g) The body tilts over the cup of water and the felt gets soaked in water once again. h) The evaporation starts again and the process continues for ever.
What will
stop the motion? Only
the following things can stop the motion. a) The surrounding is too humid for evaporation to take place b)
The water level in the
cup goes down and the bird is no more able to dip the nose and make it wet. Food for
thought..... Can this mechanism be used, somehow, for generating usable and measurable power? Ether being
highly inflamable, it is very difficult to seal the glass tube near the nose
by a gas burner. When I made this long back in 1972, the lower end of the body
was kept in a pan filled with ice while carrying out sealing on top. Even
then, the ether had caught fire twice. Finally, the sealing was successful in
the third attempt. Can you
think of any other liquid which has a low boiling point but not inflamable? Do write to
me...
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