Articles: Why Does Air Matter?
Although air is invisible, it’s actually made up of tiny parts called molecules. Most of the matter on Earth is in a gas, solid, or liquid state. Air is made up of gas molecules, so it acts differently than a solid (like a bar of chocolate), or a liquid (like water). You can feel air when you blow on your hand, and you can see that it takes up space when you blow into a balloon. Air also has mass, and you can measure it. For instance, a balloon that is only half full of air weighs less than a balloon that is fully blown up. Since air takes up space and has mass, it is matter.
Air is very important for flight. In fact, without air, an airplane couldn’t fly! Balloons can float for a short time, but all it takes is one strong gust of wind to blow the balloon out of sight. If we understand how air flows and how certain forces affect how objects move through the air, we can make things fly properly.
There are four forces in action when an airplane flies. These are called lift, weight (or gravity), thrust, and drag.
Lift is the force that pushes the airplane up as the air flows over the wings—just like a baseball cap that flies off your head when you run, or a strong wind that blows papers off your desk. Since airplanes are usually very heavy, they need a lot of lift. This is why heavy airplanes have wings that stick out to get more lift.
Weight works against this lift force. When you weigh yourself, you are actually measuring the force of Earth’s gravity on the mass of your body. Gravity is always pulling us toward the Earth, which is why we could never fall off the Earth. We feel gravity pulling us toward the Earth when we trip and fall down.
Heavy objects need more lift force to fly because of gravity. If you place a heavy book on your papers, they won’t blow away, unless that wind turns into a hurricane. If you run with a football helmet on instead of a baseball cap, you’d have to run really fast to get lots of air flowing over it before it would fly off. If the football helmet had a long visor sticking out into the wind, it would fly off sooner.
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Editor: Brian Day
NASA Official: Liza Coe
Last Updated: September 2005
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