The Drinking Bird

Is the Drinking Bird a perpetual motion machine?

Depending on what type of perpetual motion machine is being described, all perpetual motion machines violate either the First or Second Law of Thermodynamics, so the answer is no, the Drinking Bird is not a perpetual motion machine.

So what powers the Drinking Bird? If it is moving it must have kinetic energy and the Principle of the Conservation of Energy says that this kinetic energy must have come from somewhere. It does not come from the water as, despite what you might have read about “water powered cars”*, water is not a fuel and does not store or transfer energy.

The correct answer is that the Drinking Bird is powered by the ambient heat of the room it is placed in. The process that occurs is as follows:

  1. The head of the bird is placed in the water and the cloth material of its head soaks up some of this water.
  2. The water evaporates from the cloth head, lowering the temperature of the vapour trapped inside it. The movement of the head through the air as the bird oscillates back and forth helps speed up this evaporation. (The red fluid is dyed dichloromethane and the bird is evacuated during construction so that only dichloromethane and dichloromethane vapour is present in the central column.)
  3. As the temperature of the vapour decreases it turns back into a liquid, lowering the pressure inside the central column.
  4. This lowered pressure draws dichloromethane from the reservoir at the base of the bird up the central column.
  5. The fluid being drawn up the central column of the bird raises its centre of gravity and causes it to tip over.
  6. As the bird tips over, the central column becomes open to the reservoir at the base of the bird, causing pressures to equalise and the fluid to drain back out into the reservoir. At the same time the head is resubmerged into the water and the process repeats.

The Drinking Bird is a heat engine that uses the difference in temperature between the head and the base of bird to perform work, transferring thermal energy to kinetic energy. This temperature difference is created by evaporation that is powered by a room’s ambient heat. If you were able to perfectly insulate a room so that no thermal energy could enter or leave then you could cool the room down by leaving a drinking bird running.†

* “Water powered cars” are actually being powered by hydrogen fuel cells. The hydrogen comes from the water and is extracted using electricity, making “water powered cars” actually powered (indirectly) by electricity.

† Friction between the air and the bird, and between the bird and its bearings would transfer some of the bird’s kinetic energy into thermal energy, heating the room back up.

6 thoughts on “The Drinking Bird

  1. what if it was a disc shape instead of a bird, and used magnetic bearings? where would the heat go?

  2. I’m not sure how a disc-shaped drinking bird would work, but there’s always going to be some air resistance and other frictional forces that will dissipate heat.

  3. i have a bit of a beef with this seemingly constant penchant for dismissing perpetual motion with a cursory wave of the ‘thermodynamics’ hand.
    and that beef mainly stems from newtons first law which states:-
    ‘an object that is stationary will remain stationary and an object that is in motion will stay in motion at the same speed and in the same direction unless acted upon by an unbalanced force’
    so it would seem to me that newtons first defines perpetual motion as being the standard in a balanced system, and not an impossibility as thermodynamics proponents claim.

    the two ‘laws’ seem to be at odds with one another which can only mean that one of them is not a law at all, but is flawed and incorrect.

    which one is it?

    i look up at the planets and although science states that they are indeed slowing down, several other indicators appear to suggest that they are not slowing down at all.

    the Antikythera machine still accurately predicts eclipses, which after 2000 years or more should be out of synch by a notable factor?
    and other astrological methods still seem to accurately predict the position of a planet to the Nth degree

    something is wrong somewhere, my money is on the ‘law’ of thermodynamics, afterall something so complex with so many moving parts is prone to failure surely?

  4. some secondary thoughts having read this article again….

    water cannot store nor transfer energy? how is the kinetic energy from falling water transferred in a hydropower station?

    water is not a fuel? water is hydrogen and oxygen, both combustible gases, water can be split into hydrogen and oxygen by either electrolysis or sonic cavitation into browns gas, highly combustible

    and lastly, cars cannot run on water?…..once split into hydrogen hey presto, the hydrogen powered car, a reality and a fact, so yes, cars can be run on water, modified water maybe, but water none the less

  5. water cannot store nor transfer energy? how is the kinetic energy from falling water transferred in a hydropower station?

    This is nothing to do with the water. It is to do with the position of the water. It would work just the same if it were Coca Cola or petrol; the fact that it’s water is immaterial.

    water is not a fuel? water is hydrogen and oxygen, both combustible gases, water can be split into hydrogen and oxygen by either electrolysis or sonic cavitation into browns gas, highly combustible

    Water is not a fuel. The amount of energy required to separate water into hydrogen and oxygen is greater than the amount of energy returned (either by burning the hydrogen in the oxygen or using them in fuel cells) and thus it is not a fuel. If you’re going to use electricity to create a fuel, the energy of the electricity needs to be included in your calculation.

    and lastly, cars cannot run on water?…..once split into hydrogen hey presto, the hydrogen powered car, a reality and a fact, so yes, cars can be run on water, modified water maybe, but water none the less

    LOL. “Once split into hydrogen” is the important one there. Once converted into oil, plankton is a good way to power a car. Once converted into coal, dead trees are a good way to heat your house. “Modified water” is hilarious. There is no way, in any sense, that a car can run on water. I can fill up your “water-powered” car with hydrogen from anywhere, and it will still run just fine, so it is categorically not being powered by the water.

    I would – honestly – love it if we could run cars on water. But we can’t.

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