The toy bird that rocks back and forth to sip water from a cup - how does it work?

Question

Can you tell me please? I'm curious :)

Answer 1

There is an excellent description on the link.

Basically the liquid inside the bird is the key. There is a fine balance between temperature and vapor pressure inside teh glass bulbs of the bird.

To start the moisture on the beak evaporates causing a cooling of the top bulb. At the vapor in the top buld cools it condenses and shrinks in size. This lowers the pressure in the top bulb which draws liquid from the bottom bulb. This shifs the balance and the bird tips. As the bird tips the tube connecting the upper and lower bulbs gets oriented so as to allow the pressures to equalize and lets the liquid drain back into the lower bulb. The bird straightens up and the whole cycle starts again.

Answer 2

The bird is covered with an absorbent material and of course it has more area on the back end. When it puts its beak into water the water is absorbed by the covering which gets heavier due to the water. since more water is absorbed by the back end the extra weight sets the bird upright. when the water evaporates the weight in the tail diminishes and the bird is overbalanced toward the front and and so it falls forward to get another sip of water.