The Drinking Bird Demonstration

In this short video, Paul Cook shows you the drinking bird demonstration, a captivating demonstration of several scientific principles and concepts in action, showcasing how changes in temperature, evaporation, condensation, and weight distribution can create a repetitive and seemingly mesmerising motion. It serves as a fun and educational tool to engage people’s curiosity and promote an understanding of basic thermodynamic concepts.

What is the Drinking Bird?

The drinking bird, also known as a sipping bird or a dunking bird, is a popular toy or novelty item that often fascinates people with its repetitive motion. It consists of a glass bird-shaped figure with a long beak, attached to a liquid-filled glass container. The bird is usually made of colourful felt or plastic.

The drinking bird operates based on a simple but clever scientific principle called the thermodynamic cycle. The glass container is partially filled with a volatile liquid, such as dichloromethane or methylene chloride. The bird’s head is made of a porous material that absorbs the liquid from the container when it dips into it.

Here’s how the drinking bird works:

1. Starting Position: The bird is positioned with its beak pointing downwards, and its head submerged in the liquid in the glass container.
2. Evaporation: The liquid in the head of the bird evaporates due to the ambient heat in the room, turning into a gas.
3. Condensation: As the vapour rises and cools in the bird’s head, it condenses back into a liquid.
4. Weight Shift: The condensation of the vapour in the head causes the centre of mass to shift towards the head, tilting the bird forward.
5. Dipping Motion: As the bird tilts forward, its beak lifts out of the liquid, breaking the liquid’s surface tension and allowing air to enter the beak.
6. Returning to Upright Position: The weight imbalance and the upward pressure of the air entering the beak cause the bird to pivot back to its original upright position.
7. Repeating the Cycle: As the bird returns to its starting position, the liquid in the bird’s head flows back into the glass container, ready to repeat the cycle.

The process continues as long as there is enough liquid in the container to provide the necessary evaporative cooling. The repetitive dipping motion gives the illusion of the bird continuously “drinking” from the container.

The drinking bird is a classic demonstration of several scientific principles and concepts, including:

Thermodynamics: The drinking bird operates based on the principles of heat transfer and the conversion of thermal energy. As the liquid in the bird’s head evaporates, it absorbs heat from its surroundings, causing the bird’s head to cool down.

Evaporation: The liquid in the bird’s head evaporates due to the ambient heat in the room. Evaporation is the process by which a liquid changes into a gas state, and it requires energy in the form of heat. As the liquid evaporates, it cools the bird’s head.

Condensation: As the vapour rises and reaches the cooler upper part of the bird’s head, it condenses back into a liquid state. Condensation is the opposite process of evaporation, where a gas changes into a liquid due to the release of heat energy.

Thermodynamic Cycle: The drinking bird operates using a thermodynamic cycle known as the Rankine cycle. It involves the cyclic processes of evaporation, condensation, and the movement of liquid between the bird’s head and the glass container. The weight shift caused by the condensation and evaporation drives the bird’s dipping motion, creating a repetitive cycle.

Centre of Mass and Weight Shifting: The condensation of the vapour in the bird’s head causes the centre of mass to shift towards the head. This weight imbalance tilts the bird forward. As the liquid flows back into the container, the centre of mass shifts back, causing the bird to return to its upright position.

The drinking bird is a captivating demonstration of these principles in action, showcasing how changes in temperature, evaporation, condensation, and weight distribution can create a repetitive and seemingly mesmerising motion. It serves as a fun and educational tool to engage people’s curiosity and promote an understanding of basic thermodynamic concepts.

You will need:

• • 400ml beaker
  • 400ml water
  • Drinking bird toy

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