Building Science Concepts: The air around us

Air is the medium in which we live. A good understanding of the nature and properties of this substance will help students when they come to investigate and understand science concepts about air pressure, floating and flying in air and the movement of air as it relates to wind and weather conditions.

The New Zealand Ministry of Education’s Building Science Concepts (BSC) series presents sets of interlinking concepts that build stage by stage towards overarching science concepts or big ideas. A big idea shows how a fully developed understanding of the concept might look, but recognises that such an understanding might not be achieved until New Zealand Curriculum level 7 or 8.

This resource is a partial replication of Building Science Concepts Book 30 The Air around Us: Exploring the substance we live in. The background information on this page, combined with the information in the interactive, covers the science notes provided in the original BSC book. The overarching science concepts (big ideas) and how they may be scaffolded in sequence are illustrated in the interactive below.

Air is all around us even though we can’t see it

We live in a mixture of gases called air (hau takiwā) – the substance that makes up the Earth’s atmosphere (kōhauhau). Two gases – nitrogen (78%) and oxygen (21%) – make up 99% of the mixture. Gases in the other 1% include carbon dioxide (0.03%), water vapour and traces of other gases. The higher up in the atmosphere you go, the thinner or less dense the air becomes. However, the relative percentages of gases in the mixture remain the same, regardless of how dense the air is.

Living in the thick of it

The Earth’s atmosphere is about 10,000 kilometres deep. Scientists divide it into four main layers: the troposphere, stratosphere, mesosphere and thermosphere. Like water in the oceans, air in the atmosphere is thickest (most dense) at the bottom (the troposphere) and thinnest (least dense) at the top (the thermosphere). We mostly experience the atmosphere at the base layer, which is the thickest part of the thickest layer.

Vertical structure of the atmosphere

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Vertical structure of the atmosphere showing four divisions based on temperature. If, alternately, the extent of gas mixing is used, the atmosphere can be divided into two main regions.

Download a PDF version of this diagram.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Height above Earth

Air layer

Characteristics

600–10,000 km

Thermosphere: Exosphere

• Contains very few particles of air and gradually merges into the vacuum of space.

• Major orbiting area for satellites.

80–700 km

Thermosphere: Ionosphere

• Few particles of air.

• Contains layers of electrically charged particles or ions (used to bounce radio signals back to Earth).

50–80 km

Mesosphere

• Ice clouds sometimes form.

• The layer in which most meteors burn up.

10–50 km

Stratosphere

• Contains ozone layer in upper parts (Earth’s main UV sunscreen).

0–10 km

Troposphere

• Greatest concentration of air.

• The layer in which most clouds form and most weather takes place.

Layer of insulation

The atmosphere is often referred to as a blanket wrapped around the globe because of its insulating qualities. It protects the Earth from most of the ultraviolet radiation from the Sun. It also buffers the Earth against extreme heat gain from the Sun’s radiant energy during daytime and against extreme heat loss during the night.

Aurora Australis over Lake Tekapo

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The colours of the Aurora Australis are caused by the reaction of the gases in our atmosphere with the solar winds that are emitted by the Sun.

Rights: Fraser Gunn

Air is pushy stuff

Air has weight. The air in the atmosphere is ‘thickest’ at the Earth’s surface because the weight of the air in the atmosphere above is pushing down on it as gravity pulls it to Earth. This is called atmospheric pressure (pēhanga kōhauhau).

Air pressure can be used to do work. Compressed air drives pneumatic drills, dentist drills and truck brakes and even opens some doors on buses. Blowing up a balloon and then releasing it shows the force of the air pushing the balloon around the room. The force of the escaping air (moving from an area of high pressure inside the balloon to the lower pressure outside) propels the balloon away from the point of release.

Air in space

Air behaves in the same way as any other fluid (wē). It flows and spreads into spaces that are not otherwise occupied. Air is not just all around us, it is in everything around us. Empty space at the Earth’s surface might look empty, but it is almost always filled with air.

Squashing air

Unlike fluids such as water, air can be made to squash into a space. For example, a bicycle tyre contains only so much space. As you pump the tyre up, you force more and more air into that space. The incoming air is compressed (kurutē) to fit in to the space available. This increases the air pressure. This increased pressure makes the tyre feel firm as it is hard to compress the air any further. In this type of pneumatic (air-filled) tyre, the air is usually held in by a valve (katirere). Air under pressure (compressed air) can support a lot of weight. At the same time, it can absorb impact by compressing further when, for example, a tyre hits a bump in the road.

Bike tyres and air pressure

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A bike pump compresses air and pushes it into the bike tyre. There is more space between air particles, so they can be pushed together.

Rights: romannerud, 123RF Ltd

Cold air, warm air

Cold air particles can pack together more closely as they move more slowly and bounce with less force. Cold air is therefore more dense and heavier than the same volume of warm air. Air particles tend to move from areas of dense high pressure to areas that are less dense and lower pressure. These are some common examples of this phenomenon:

• In a house, you find cooler, denser air near the ground and warmer, less-dense air near the ceiling.

• Denser, high-pressure air in a balloon escapes to less-dense, lower-pressure air when the balloon’s neck is released.

• To rise and float, a hot-air balloon uses a burner to adjust the air to become less dense. To sink, it uses a release valve at its top to let out its least-dense air and bring in more-dense air.

Air on the move

Air flows from areas of greater density (higher pressure) to areas of lesser density (lower pressure). This produces the phenomenon of wind (hau). Wind is air that is moving. Onshore and offshore breezes show this in action. The land heats during the day, warming the air above, which rises. Cooler air flows in from the sea to replace it, creating an onshore breeze. At night, the reverse happens. The land cools more rapidly than the sea, the warmer air above the sea rises and the cooler air from the land flows in to replace it, creating an offshore breeze.

Te ao Māori connections

In te ao Māori, the air is part of the domain of the deity Tāwhirimātea, who is known as the god of the weather. There is much mātauranga associated with the changes in the weather and the phenomena that occur in the sky. Much of that knowledge is localised, so it is appropriate to enquire locally to discover and learn about the tohu or signs of your region or rohe.

Download the PDF Kuputaka Māori mō te hau takiwā – a list of glossary terms associated with the air.

Alternative conceptions

Some students think that the atmosphere is the same thing as cloud cover. The atmosphere is invisible to the naked eye. Clouds form (and are visible) when water vapour in the lower atmosphere condenses into tiny droplets.

Students can sometimes think that, if the amount of air is unchanged, the air volume will not change. This concept does not allow for the compression of air.

Sometimes students can believe that air pressure will increase with altitude when in fact the opposite is true.