Summer is meant for swimming, barbecues, and yes, flying kites. The warm weather is the perfect time to take advantage of a breezy summer evening at the park – and you can even slip a little bit of science into your kids’ subconscious, by explaining just how a kite manages to fly!
There are actually several bits of physics at play here and, interestingly, they’re the pretty much the same physics that help lift an airplane off of the ground. These are also known as the four forces of flight.
The first, of course, is lift. Basically, the wind blows on your kite – some of it hits the kite directly, some goes over the kite, and some goes under it. The wind that goes underneath helps lift the kite off the ground, just like the wind beneath an airplane’s wings helps lift it off the ground. Sometimes, when there is not enough wind to lift a kite, you need to run with it, creating your own bit of wind behind you.
The flip side of lift is drag (they go together like peas and carrots). Lift is the force that, well, lifts an object up; drag is the pressure of the wind against that object that keeps it aloft. The purpose of aerodynamics is to reduce drag, but a kite is designed to offer just enough lift and drag to get it – and keep it – in the air.
On the way home from the park, roll down the window and have your kidlet point his hand outside, elbow resting on the windowsill, arm at a 90 degree angle. The push he feels on the fingertips of his flat hand is drag. The pressure he feels lifting his hand up and backward is lift.
Weight defines the force of gravity holding your kite to the ground. Kites are generally lightweight, so that the wind can easily overcome gravity and lift the kite into the air. Ask your kiddo what she thinks would happen if the kite weighed, say, as much as a puppy.
Thrust is the force that pushes your kite in a forward direction. Thrust is created either by the wind driving the kite forward or by your child pulling the kite forward with the string.
To get your kite into the air, the force of the lift must overcome the force of gravity holding the kite down; to keep it in the air, the force of thrust must be equal to the force of drag.
Although not one of the four forces of flying, directionality is also important when flying a kite. Have your child face the wind and try for lift off – odds are, the kite will just toss and tumble behind her. Now, have your child turn her back to the wind and watch as the wind rushing at the kite surrounds and lifts it off the ground.
Stability is another key piece of kite flying physics. Point out to your fearless flyers that the kite’s string is attached at three different points on the kite – the center, and both sides, probably near the rear of the kite’s body. This helps keep the kite from flapping, twisting, and turning in the wind. It helps keep the kite stable. The tail of the kite also helps provide stability by keeping the kite in line with the wind. Ask your kiddo what he thinks would happen if the kite were attached at just one point or if it didn’t have a tail.
Lift, drag, thrust, and weight. Stability and directionality. Important physics concepts that are easy to demonstrate with your kite. So what are you waiting for? Let’s go fly a kite, up to the highest heights…