The Incredible Drinking , Bobbing Bird - An Operating Heat Engine

The term "Go soak your head" takes on a whole new meaning for the Incredible Drinking Bobbing Bird. Soaking it's head is what brings it to life, bobbing up and down incessantly. And as long as a full glass of water is placed so the bird can continually soak it's head, it will continue bobbing its head for another drink as long as it can reach the water. But what makes it work? Is it the elusive Perpetual Motion Machine? Magic? The solution to the incredible Drinking Bird's operation is neither of these two answers. It is a simple representative of an apparatus scientists call a heat engine.

The Bird's construction is quite simple. It consists of two glass globes connected by a clear glass tube. The lower globe is half filled with liquid. The tube between the globes extends below the level of the liquid in the lower globe. The upper globe is covered with felt. The legs of the bird allow the axle which holds the body of the bird to turn freely.

The heat engine uses the evaporation of water to provide the energy needed to operate it. Evaporating water removes heat from its surroundings as it evaporates. When the felt head of the bird is soaked in water, it begins to evaporated immediately, cooling the air in the globe which forms the head of the bird. When this cooling occurs, the pressure in the globe drops. The liquid in the lower globe is pulled by the lowering pressure into the upper globe.

As the liquid collects in the upper globe, it weights the upper globe until it is heavier than the lower globe. This causes the bird to tilt forward on the axle. When the bird tilts forward, the pressure equalizes between the two globes and the liquid returns to the lower globe causing the liquid to return to the lower globe. This causes the lower globe to be heavier, bringing the bird back upright. The device is called a heat engine because of the heat removal action of the evaporating water, which causes the device to operate.

As long as the glass in front of the bird is placed so the felt beak dips in it, and the water is kept replenished, the bird's head will stay wet, and the bird will continue to operate.

Sometimes a minor adjustment is needed when the bird is set up the first time. The metal strips on the side of the bird which form the axle may slightly forward of backward to balance the bird properly. That is about the only adjustment which needs to be made.

So, soak the birds head, put some drinking water in front of it, and watch it go! And who says science ain't fun.