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# Birds in Flight: How Birds' Wings Enable Them to Fly (page 2)

By Pam Walker | Elaine Wood
John Wiley & Sons, Inc.

Birds' wings, like airplane wings, have a specific shape that makes them perfect for flight. Air travels faster around the upper curved surface of the wing than it does around the lower flat surface. This reduces the air pressure on top of the wing. The greater air pressure below the wing lifts the bird upward in flight. The differences in air pressure above and below a wing are explained by Bernoulli's Principle, which states that as air speed increases, air pressure decreases. This activity will demonstrate how Bernoulli's Principle allows birds to fly.

### Materials

Two empty soda cans

### Activity

1. Place two empty soda cans on their sides on a table so that the bottoms of the cans are facing you. Position both cans with only a small space between them.
2. Predict what will happen if you blow in the space between the cans.
3. Blow in the space between the cans so the stream of air travels along the length of the cans. Notice what happens to the cans.

### Follow-Up Questions

1. What did you predict would happen if you blew in the space between the cans?
2. What actually happened when you blew between the cans?
3. How does this activity demonstrate what happens to air that travels around the bird's wings when it is in flight?
4. What are the similarities between an airplane's wings and a bird's wings?

1. Answers will vary, but most students predict that the cans will separate.
2. The cans moved together.
3. An increase in velocity between the cans reduces air pressure and the cans come together, rather than fly apart. The upper curve of the wing makes air travel faster around the top surface than it does around the lower surface. This reduces the air pressure on top of the wing. The greater air pressure below the wing lifts the bird upward in flight. The differences in air pressure above and below a wing are explained by Bernoulli's Principle, which states that as air speed increases, air pressure decreases.
4. Both are successful based on Bernoulli's Principle.

### Extension

Not all birds are able to fly. Do some research and find out why some birds can fly, but other birds cannot. Base your explanation on Bernoulli's principle.

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