The air we breathe Lesson 33 of the chemistry course of Mova's primary school: 19 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: the lesson at school .
0 Wave your hand fast and you feel something push back: air. 2 Push an "empty" glass upside down into a bowl of water and the water will not fill it, because the glass is full of air. 3 Old diving bells kept people dry under water the same way. 4 Air is mostly nitrogen, which hardly reacts, with about a fifth oxygen that we breathe, and tiny amounts of other gases such as carbon dioxide, which plants take in and which traps heat like a blanket. 5 Air can get dirty with smoke and fumes, and people have changed it: we put holes in the ozone layer and are adding carbon dioxide. 6 Yet when the world agreed to act, the ozone layer began to heal. 7 Air is a mixture of gases; it takes up space and has weight, even though you cannot see it. 8 About 78 parts in 100 of air are nitrogen, about 21 are oxygen, and about 1 is other gases; carbon dioxide is only a tiny part. 9 Nitrogen hardly reacts, so crisp packets are filled with it to keep the crisps fresh. 10 Air presses on us from all sides, and the air and liquids inside our bodies press back out, so we do not feel its weight. 11 High on a mountain the air is thinner, so each breath holds less oxygen; climbers on the highest mountains often carry oxygen tanks. 12 Smog is a dirty haze of smoke and car fumes that builds up in still air; cleaner cars and fuels have made many cities' air clearer. 13 The ozone layer, high in the sky, blocks much of the Sun's harmful ultraviolet light; some old spray-can and fridge gases damaged it. 14 Those gases were banned by a world agreement in 1987, and the ozone hole has been reported to be slowly healing. 15 Burning coal, oil and gas adds carbon dioxide to the air; carbon dioxide traps heat like a blanket, so even a small rise warms the planet. 16 Plants take in carbon dioxide and give out oxygen while they use sunlight to make sugar; tiny plants in the ocean are thought to make about half of the world's oxygen. 17 A few houseplants do very little to clean the air of a room; opening a window does far more. 18 Fridges and air conditioners use special gases that soak up heat when they evaporate and give it out when squeezed; old fridges are recycled carefully so these gases do not escape. 19 Air is full of tiny specks of dust, pollen and skin flakes; you see them dancing in a sunbeam because they reflect light, and pollen makes people with hay fever sneeze. ← previous Recycling: giving materials a second lifenext → Water: the most amazing liquid↑ back to Chemistry This page in Markdown → https://md.mova.elamur.ai/free/en/corpora/school/chemistry/33-the-air-we-breathe/