Every day we get to see the magic of flight. When you stop and think, it’s truly remarkable that even the smallest of birds gets to see the world from above as they swoop and dive through the air. It’s a perfectly logical question from a young child to ask, “how do birds fly?”. Do you know the answer?
When birds fly, they are achieving two things at the same time; lift and thrust. Lift is the term for rising upward in the air, while thrust refers to moving forward. Unsurprisingly, it is the bird’s wings which enable it to achieve both of these feat.
The wings of a bird and an airplane work in the same way to lift off the ground. They share a similar shape; thicker on the leading edge, tapering to a point on the opposite side. They are also slightly curved, with the rear point finishing lower than the front edge. This shape is called an air foil. An airplane’s wing does not move because it uses its engines to generate thrust instead. This makes it a bit simpler to understand how lift is generated from a plane wing, but remember that it’s the same physics for a bird too.
When a plane is going to take off, it starts to roll along the runway at increasing speed. As it does so, the wing moves forward through the air, forcing the air to move around it. Some of the air goes over the top of the wing, traveling over the convex edge and the rest moves under the wing, following the upward curving concave edge. The air which travels across the top of the wind is squashed into less space, making it flow faster. By flowing faster, less air is able to be in contact with the top of the wing, so less force is pushing downward. In contrast, the shape underneath the wing means that the air actually has more space and so flows more slowly. This causes more air to be in contact with the underside of the wing, increasing the force which is exerted upwards. With a greater force pushing up than pushing down, the wing is lifted upwards, taking the plane/bird with it. This video explains this concept really clearly:
By moving its wing, a bird is able to increase the amount of lift it generates, helping it to take off or rise higher in the sky. This movement also adjusts the angle that their wing is positioned. It means that rather than pushing upward at 90 degrees, the lift they generate pushes up at an angle, moving them forward as well as up. This is how a bird generates thrust.
The Children’s Answer
To explain how birds fly to young children, you will need to break the answer down into logical steps which can each be clearly demonstrated. Begin with the most simple principle – if forces are pushing into one another, the strongest force wins. You can demonstrate this idea in all sorts of ways; ask a child to put their hand against yours and push as hard as they can. Show that if you push hard, you are stronger and can move them, but if you push more gently, they win. Explain that a bird’s wing is shaped in such a way that it makes the air push harder upwards that downwards.
Demonstrating to children that when air moves fast over the top of a birds wing, it pushes down more gently is surprisingly easy. Hand each child a single piece of paper, and ask them to hold it by the short edge. Take your own piece of paper and hold the short edge in front of your lips. Position yourself side on to the group and blow gently across the top of the paper. The sheet will flutter and then curve upwards. Explain to the children that by blowing the air across the top, you are making it move faster and therefore press down more gently. Because the air pushing up is stronger, the paper moves up. Encourage the children to try this for themselves.
Complete your simplified explanation by telling the children that by flapping their wings, birds make the air move quickly over the top, lifting them up into the air. There are all sorts of ways you can build on children’s interest in birds and flight: