How Do Birds Fly?

Words to Know

Lift

The force that pushes a bird UP into the air

A bird's wing shape creates lift when air moves over it.

Thrust

The force that pushes a bird FORWARD

Birds get thrust by flapping their wings.

Gravity

The force that pulls everything down toward the ground

Birds must make enough lift to beat gravity.

Hollow bones

Bones that are mostly empty inside, making birds light

Hollow bones help birds stay light enough to fly.

Check What You Learned

Fun Facts

• Birds fly using four forces: lift (up), thrust (forward), gravity/weight (down), and drag (backward).

  Source: NASA

• A bird's wing has an airfoil shape — curved on top, flatter on the bottom. Air moving over the curved top travels faster, creating lower pressure above the wing, which generates lift.

  Source: Smithsonian National Air and Space Museum

• Thrust is generated by flapping wings. Each downward stroke pushes air backward and downward, propelling the bird forward and upward.

  Source: Cornell Lab of Ornithology

• Many birds have hollow bones (pneumatized bones) with internal strut-like structures, making them lightweight but strong.

  Source: American Museum of Natural History

• Hummingbirds can flap their wings up to 80 times per second, allowing them to hover in place.

  Source: National Audubon Society

• Soaring birds (hawks, eagles, vultures) use thermals — columns of rising warm air — to gain altitude without flapping.

  Source: Cornell Lab of Ornithology