Flight

Air has weight and it is made out of molecules that are constantly moving, which creates air pressure. The movement of air allows kites and balloons to move up and down. The air is made up of a mixture of gases such as oxygen, carbon dioxide, and nitrogen. Everything that flies needs the power from air to pull and push, whether it's an airplane, kite, balloon, or bird. Because of the weight of air, it is possible for airplanes, kites, and balloons take flight.

Hot air is lighter than cool air, and this is how a hot air balloon can fly. When hot air expands and spreads out, like in the hot air balloon, it becomes lighter than the cool air and begins to rise. When the hot air becomes cool, it is let out of the balloon and the balloon begins to fall or come back down.

When a hot air balloon needs to rise, propane gas is used to heat up the air inside the balloon. Once the air is warmer than the outside air, the balloon will begin its ascent, rising into the air. When the balloon needs to start its descent, or come back down, the pilot of the balloon releases some of the hot air from the balloon. The cooler the air becomes inside the balloon, the faster the descent to the ground.

Finally, if the balloon needs to change directions horizontally, the pilot will guide the balloon to different altitudes, where the wind blows in different directions. The balloon will then simply move with the wind in the same direction.

If a kite is released into the air and it falls to the ground, gravity can be blamed. When it begins to fly, though, it is the wind lifting it into the air. It is called lift when the wind pushes against an object and carries it upwards.

There are four forces that affect the flight of airplanes: Thrust, Lift, Drag, and Weight. Thrust is produced by the engines of a plane, leading to lift, which is the force normally moving the airplane upward. Lift is produced by the forward motion of the plane through the air. Drag is a force created by the resistance of the air to the forward motion of the plane. Finally, weight is the pull of the Earth's gravity on the plane. Without the four forces, the plane would not be able to stay in the air.

When a kite flies, the wind is getting it into the air. For an airplane, though, thrust helps get it into the air, causing the plane to lift, or take-off. As the plane flies, thrust continues against the resistance produced by the force called drag. At the same time, due to gravity, weight is trying to force the plane to be pulled down. However, the force of lift, because of the motion produced by the thrust of the engines, is greater than weight, so the plane moves upward.

Every part of an airplane can produce lift, but most of it comes from the wings of the plane. There are many different kinds of airplanes, and some of them have more powerful engines than others. There are also planes with propellers, and some that do not have propellers. All of the planes, however, fly because of the same four forces: Thrust, Lift, Drag, and Weight.

A brief history of flight includes the first kite flown by the Chinese nearly 2,500 years ago during religious ceremonies. They were also built for fun and to test weather conditions. At about the same time, other humans were trying to fly like birds, making wings out of feathers, and of course they failed. The first hot air balloon flight took place in 1783 and rose 6,000 feet into the air and traveled about 1 mile. Finally, the first airplane invented by the Wright brothers lifted off the ground in 1903. There have been many advances and innovations for humans to fly through the air since the first kite 2,500 years ago.