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Bill Nye Demonstration:  Dunking Bird

Bill Nye Demonstration: Dunking Bird

Author: Bill Nye

This lesson explores the mystery of one of my favorite science toys, the Dunking Bird. 

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The Dunking Bird

Why would a bird with a blue hat be so thirsty? It's not the hat, it's SCIENCE!

How it Works

When the bird is manufactured, most of the air is removed from the inside. The gas that remains is largely the vapor from the red liquid, which vaporizes very easily. When the fuzzy coating on the bird's head is wet, water evaporates and cools the vapor inside the bird's head. This condenses the vapor back to red liquid and reduces the pressure in the bird's head. When the fuzzy coating on the bird's head is wet, water evaporates and cools the vapor inside the bird's head. This condenses the vapor back to liquid and reduces the pressure in the bird's head. The bird's head keeps moving.

Since the pressure of the vapor in the bird's body is now higher than the pressure in its head, liquid is forced from the bottom up the tube toward the head. As the liquid moves up the tube, the center of gravity of the bird is raised, and the bird begins to tip around its fulcrum. When the bird finally dips into the water, a clear passage is opened between the head and the body, allowing the pressures to equalize and the liquid to fall back down to the body. The bird returns to the upright position and the whole process repeats.

Each time the bird's beak dips into the water, the fuzzy material absorbs a little water to replace any that has evaporated. This prevents the bird's head from drying out. The bird will continue its cycle until the head dries out, and evaporation can no longer cool it.

In summary, here are the basic steps of the cycle.

  1. The Dunking Bird's head gets wet. 
  2. When water evaporates from the fuzz on the Dunking Bird's head, the head is cooled.
  3. The temperature decrease in the head condenses the methylene chloride vapor, decreasing the vapor pressure in the head relative to the vapor pressure in the abdomen.
  4. The greater vapor pressure in the abdomen forces fluid up through the neck and into the head.
  5. As fluid enters the head, it makes the Dippy Bird top-heavy.
  6. The bird tips. Liquid travels to the head. The bottom of the tube is no longer submerged in liquid.
  7. Vapor bubbles travel through the tube and into the head. Liquid drains from the head, displaced by the bubbles.
  8. Fluid drains back into the abdomen, making the bird bottom-heavy.
  9. The bird tips back up.
  10. It all starts again!

How Cool is That?

Daniel Reynolds giant drinking birds, 6.5 feet tall. Created in 1998, these guys are truly impressive.

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Check out more explanations and extensions!


What Else is There?

If you're interested in watching more of my demonstrations, checkout my playlist,

Science Demonstrations by Me, Bill Nye


Your Turn!

Have cool science demonstrations you show your classes regularly? Save time and materials by making a quick video tutorial of your own for students. By using demonstrations and lab investigations regularly, students not only will know science, they can apply it!

Check out some resources on doing it yourself: