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Characteristics and Pressure of Air

This text explains the characteristics of air, including its composition and importance in combustion and life support. It also explores the concept of air pressure and includes experiments to demonstrate how air exerts force.

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Characteristics and Pressure of Air

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  1. Air WALT: to know some of the characteristics of air WILF: to understand that air exerts pressure

  2. Air • Air is a mixture of different gases • Including nitrogen, oxygen, carbon dioxide, water vapour • There are other gases that are useful but come in very small quantities

  3. Air is important in allowing things to burn

  4. The oxygen in the air is needed to keep the fire going, but it is the fuel that is burning. • Oxygen itself can’t burn. It has to combine with something else • Why is oxygen only 21% of air? If it were any more, fires would break out spontaneously all over, any dryness and slight heating and, whoosh, up in flames.

  5. Fish need air that is in water to live

  6. Air can be squeezed into a balloon so that it pushes on the rubber, stretching it and making the balloon get bigger

  7. Oxygen could be described as our most important gas • It supports the life of plants and animals • Pure oxygen is also used to treat patients with breathing difficulties, to support mountaineers and deep sea divers

  8. Nitrogen is used in the food industry • Many foods are packed in atmosphere of nitrogen because this stops the food “going off” • When you open a bag of crisps you may be letting out nitrogen into the atmosphere

  9. Air Pressure • Air pressure is all around us as we live under a "sea of air" - a bit like a fish surrounded by a sea of water. • The air presses on us from all sides, but we are so used to it we don't feel it. Every part of our body is pushing back (each cell is like a balloon) so we don't get squashed flat.

  10. Experiments • Target: what are we trying to find out? • To show that air exerts pressure or force

  11. Experiment Materials • What do you need? • A tank of water • An empty drinking bottle • A plastic bottle with a hole in it • Tumbler and a piece of paper • A straw

  12. Experiment 1 • What is in this bottle? • How can I prove that there is air in it? • Lower it below the surface of the water in the tank • When the bottle is tilted bubbles are forced out showing that air is present • Pressure of the water forces the air out

  13. Experiment 2 • Bottle with hole • First of all we are going to fill it with water. What do you think will happen? • Why? • The air pressure is pushing the water out of the hole • Demonstration

  14. Now I cam going to put my hand over the top of the bottle. What do you think will happen? • Demonstrate- Why has this happened? • The air isn’t pushing down, the air pressure is blocked so the water doesn’t come out the hole

  15. You have a cup and piece of paper. How can you put the paper in the water without getting it wet? • Screw a sheet of paper, putting it in the tumbler so that it is a snug fit and won’t fall out of the tumbler • Why does the paper stay dry? • The tumbler is full of air and the air push is keeping the water from rising up inside the tumbler

  16. Experiment 4 • Take a straw and suck some water into it • Hold it over a sink or container with your finger firmly covering it up • What do you think will happen? • The water remains in the straw • Why?

  17. When your finger is not on the top of the straw air pressure pushes down and up the straw through both openings and so is balanced • Gravity then makes the water fall • If you block off the top of the straw, then air pressure can only push from the bottom. • It is stronger than Earth’s gravity so it keeps the water in the straw

  18. Well done scientists! • Now for the write up!

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