Lesson 1 Introduction
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Have you ever thought about how interesting air is?
Air is all around us, but we cannot see it. That is because air is mostly a gas. Think about what happens when you blow up a balloon. The balloon expands because air molecules, which are too tiny to see, take up space.
Air changes as you go higher. Air seems light, but in the atmosphere, it is pushing down on the Earth's surface. The atmosphere is the layer of gas that surrounds Earth.
All the molecules of air in the atmosphere above your head weigh something. The weight of the air above your head is approximately 245 kg of air, the weight of a small car. Fortunately, air flows around objects and pushes them in all directions. This balances the downward force on our bodies so we don't collapse. The pushing force is called air pressure. The higher you go, the less air pressure there is pushing down on you.
Air is all around us, but we cannot see it. That is because air is mostly a gas. Think about what happens when you blow up a balloon. The balloon expands because air molecules, which are too tiny to see, take up space.
Air Pressure
Air changes as you go higher. Air seems light, but in the atmosphere, it is pushing down on the Earth's surface. The atmosphere is the layer of gas that surrounds Earth.
All the molecules of air in the atmosphere above your head weigh something. The weight of the air above your head is approximately 245 kg of air, the weight of a small car. Fortunately, air flows around objects and pushes them in all directions. This balances the downward force on our bodies so we don't collapse. The pushing force is called air pressure. The higher you go, the less air pressure there is pushing down on you.
Air Temperature
Feeling the difference between hot and cold air is not difficult, but not everyone understands how temperature affects the air. Temperature affects the density (the closeness of the molecules) of air, which in turn has an effect on whether air rises or sinks.How temperature affects air density is simple.
If you warm air, it increases in size or volume (expands). The air molecules move faster and become farther apart (less dense). The air pressure is lighter.
If you cool air, it shrinks. The air molecules move slower and become closer together (become denser). The air pressure is heavier.
Cold air sinks, and hot air rises! That means that warmer air expands and rises and cooler air shrinks and sinks. In other words, cool air is closer to sea level. Warm air is higher.
If you warm air, it increases in size or volume (expands). The air molecules move faster and become farther apart (less dense). The air pressure is lighter.
If you cool air, it shrinks. The air molecules move slower and become closer together (become denser). The air pressure is heavier.
Cold air sinks, and hot air rises! That means that warmer air expands and rises and cooler air shrinks and sinks. In other words, cool air is closer to sea level. Warm air is higher.
The secret to hot air ballooning is to
heat
the air inside the balloon.
A wonderful example of this
is a hot air balloon.
A hot air balloon has a burner in the basket that heats the air. The more you heat the air, the less dense it becomes, and the faster it will rise. When a hot air balloon has been in the air for a while and it's time to come down, the operator
stops heating the air and releases some of the hot air through a vent at the top. With air that is cooling in the balloon, it begins to sink.
Video
Watch this video - How does a hot air balloon work?