Earth is surrounded by a layer of air which is like a huge ocean of air. It extends to almost hundreds of kilometres above the surface of the Earth. This layer of air that surrounds Earth is called the atmosphere. The atmosphere is made up of several layers of air containing mixtures of different gases.
Gas Composition: About one-fifth (nearly 21%) of the air is oxygen, nearly four-fifths (78%) is a gas called nitrogen, and the rest is made up of argon, carbon dioxide and small amounts of other gases.
Oxygen is an important gas. It helps all living things stay alive (breathing and cellular respiration), and helps things burn (combustion).
Interactive Lab 30.1
🔬 Atmosphere Composition & Layers Explorer
Click the gas slices in the pie chart to inspect air gases, and drag the altitude slider to travel through the lower atmospheric layers!
Nitrogen (78%)
Nearly 4/5ths of the Air
Nitrogen is inert, prevents rapid burning on Earth, and is essential for building proteins in plants and animals.
✈️
Troposphere (0 - 12 km)
Contains 99% of all water vapour and weather clouds. Where life breathes and plants perform photosynthesis!
Layers of the Atmosphere (1 to 3)
1. Troposphere: The troposphere reaches a height of, on average, 12 kilometres from the surface. In addition to containing 99 percent of all water vapour and aerosols, this very thin layer is responsible for holding all the air that animals and plants need to breathe for photosynthesis.
2. Stratosphere: The stratosphere, which lies between 12 and 50 kilometres above Earth's surface, is best known as the location of the ozone layer, which shields humans from Sun's damaging UV radiation. In addition, it's the highest point in the atmosphere that jets can fly to.
3. Mesosphere: The mesosphere, which is between 50 and 80 kilometres above Earth's surface, becomes steadily colder as height increases. This layer's top is the coldest location on Earth (-90°C). The mesosphere can be reached by sounding rockets and rocket-powered aircraft.
📝 Page 30 Quick Quiz (5 Questions)
Test Your Knowledge
1. What is the thick layer of air that surrounds the Earth called?
2. Nearly four-fifths (approx. 78%) of the air is made up of which gas?
3. Which layer contains 99% of all water vapour and all weather events?
4. The ozone layer that shields Earth from harmful UV rays is located in the:
5. Which layer has the coldest temperatures on Earth and is reached by sounding rockets?
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31
Upper Atmosphere Layers (4 and 5)
4. Thermosphere: The thermosphere is located between 80 and 700 kilometres above the surface of the Earth. It is devoid of both clouds and water vapour. In the thermosphere, the International Space Station (ISS) revolves around the Earth.
5. Exosphere: The exosphere, the uppermost layer of Earth's atmosphere, lies between 700 and 10,000 kilometres above the planet's surface and combines with the solar wind. The exosphere is where most of Earth's communication and weather satellites orbit.
Atmospheric Pressure
The large mass of air in the atmosphere is heavy and presses down hard on Earth. Scientists call this weight of air the atmospheric pressure.
Vital Rule: Air pressure is greatest at sea level and decreases as we go higher up into the mountains and sky. It pushes from all sides on everything. Air exerts pressure in all directions at the rate of about 1 Kilogram per square centimetre (1 kg/cm²).
Interactive Lab 31.1
🛰️ Orbit Viewer & Altitude Pressure Gauge
Drag the altitude gauge from Sea Level to High Altitudes to watch how air molecules thin out and pressure drops!
Air Molecule Density Chamber
Atmospheric Pressure
1.03 kg/cm²
Sea Level (Standard Pressure)
Currently showing Sea Level & Weather layer.
📝 Page 31 Quick Quiz (5 Questions)
Test Your Knowledge
1. In which cloudless atmospheric layer does the International Space Station (ISS) orbit?
2. The uppermost layer extending up to 10,000 kilometres where satellites orbit is the:
3. What do scientists call the weight of air pressing down on Earth?
4. Where on Earth is atmospheric pressure the greatest?
5. Air exerts pressure in all directions at sea level at an approximate rate of:
Unit 4: Air
32
To Prove that Air has Weight
Take two rubber balloons of equal size and fill them with air. Hang them on a wooden ruler with the help of strings so that the ruler balances horizontally. Now prick one of the balloons with a pin.
Observation: The ruler will tilt towards the balloon with air in it, clearly showing that air has weight!
Interactive Lab 32.1
🎈 Balloon Balance Scale Simulation
Click the "Prick Right Balloon" button to pop it with a needle and watch the ruler tilt towards the heavy balloon!
💥 POP!
Both balloons are inflated. The ruler balances evenly.
Effects of Atmospheric Pressure
Why aren't we crushed by this pressure on our bodies?
Because we have an equal amount of pressure inside our bodies! The fluids and gases inside our body cells have their own pressure. Internal body pressure pushing outward = air pressure pushing inward.
Changes in air pressure cause changes in weather: On the surface of Earth, air always moves from areas of high pressure to areas of low pressure.
Temperature effect: As warm air rises, it produces an area of low pressure near the ground. Cooler, denser air moves down to take its place.
Mountain Climbers: Mountain climbers have to breathe heavily at mountain tops because of low air pressure, so they have to take air oxygen tanks with them.
📝 Page 32 Quick Quiz (5 Questions)
Test Your Knowledge
1. In the balloon experiment, why does the wooden ruler tilt after one balloon is popped?
2. Why are humans not crushed by the heavy atmospheric pressure?
3. Across Earth's surface, wind always moves from regions of:
4. What kind of pressure zone is created near the ground when warm air heats up and rises?
5. Why do mountain climbers carry oxygen tanks with them?
Unit 4: Air
33
Measuring Air Pressure
Air pressure is measured by an instrument called a barometer. There are various kinds of barometers.
The Simple Mercury Barometer
A simple barometer consists of a long glass tube which is sealed at one end. It is filled with mercury and inverted in a dish containing mercury.
Standard Sea Level Reading: The height of the column of mercury in the glass tube measures the atmospheric pressure, which is equal to 760 millimetres (760 mm) of mercury at sea level.
Operation: The height of the mercury column moves UP when atmospheric pressure increases and moves DOWN when atmospheric pressure decreases.
Interactive Lab 33.1
🌡️ Interactive Simple Mercury Barometer
Slide the weather pressure dial from Stormy (Low Pressure) to Clear/High Pressure and observe the mercury column level!
790 mm775 mm760 mm (Normal)745 mm730 mm
Mercury Column Height
760 mm Hg
Standard Atmospheric Pressure (Fair Weather)
Stormy (720)Sea Level (760)Very High (790)
📝 Page 33 Quick Quiz (5 Questions)
Test Your Knowledge
1. What instrument is used to measure atmospheric pressure?
2. Which dense silvery liquid is used inside a simple barometer?
3. What is normal atmospheric pressure at sea level measured in millimetres of mercury?
4. When air pressure increases, what happens to the height of the mercury column?
5. A sudden drop in the mercury column usually signals what kind of weather?
Unit 4: Air
34
Uses of Air Pressure
1. To forecast weather with the help of barometers: When the atmospheric pressure in an area is low, air from a region of high pressure comes to fill it. This causes strong windstorms.
2. To suck liquids through a straw: When we use a straw to suck liquid from a glass tumbler or bottle, the air inside the straw is removed and the pressure inside it becomes less than that of the air outside. This air pressure acts on the surface of the liquid and forces it up through the straw into the mouth.
3. To fill medicines in syringes: When a syringe has to be filled with medicine, the plunger is pulled and the needle is inserted in the rubber stopper of the medicine bottle. The plunger is pushed to fill air in the bottle. As the plunger is pulled back again, medicine fills in the piston of the syringe due to air pressure.
Interactive Lab 34.1
🥤 Straw & Syringe Mechanics Lab
Click "Suck Through Straw" to see atmospheric pressure push juice up into the straw!
How It Works:
Sucking removes air inside the straw.
Pressure inside straw drops below outside air pressure.
Outside atmospheric pressure pushes down on the liquid in the tumbler.
Liquid is forced upward into your mouth!
📝 Page 34 Quick Quiz (5 Questions)
Test Your Knowledge
1. When drinking through a straw, what forces the liquid up into the mouth?
2. When you suck through a straw, the pressure inside the straw becomes:
3. Why is air injected into the medicine bottle before drawing medicine into a syringe?
4. What causes sudden violent windstorms according to the textbook?
5. Which everyday medical tool operates directly by using air pressure differences?
Unit 4: Air
35
Activity: To Show that Air Pushes Upwards
You will need a drinking glass and a piece of cardboard. Fill a glass right to the top with water. Put the card flat over the mouth of the glass. Hold the card firmly in place and carefully turn the glass upside down. Remove your hand from the card.
Result: It will stay in place! The water does not fall out because the air below the card pushes it upwards to keep it firmly in place.
Interactive Lab 35.1
🥛 The Inverted Glass & Cardboard Trick
Click the step buttons to fill the glass, apply the cardboard, flip it, and remove your hand!
⬆ ⬆ ⬆ Air Pressure
Glass is filled to the brim with water.
Air Pollution
Unwanted and harmful substances in the air cause air pollution.
Main Sources: The main source of air pollution is the burning of coal and oil in houses, factories, power stations and vehicle engines.
Harmful By-products: When burned, they produce soot and smoke and a mixture of poisonous gases, which are carried in the air for a long time.
Health Effects: They cause breathing problems, allergies, and severe lung diseases.
📝 Page 35 Quick Quiz (5 Questions)
Test Your Knowledge
1. In the inverted glass experiment, why does the cardboard stay attached to the glass?
2. For the inverted cardboard trick to succeed, how full should the glass be?
3. What is the primary source of air pollution mentioned in the textbook?
4. Burning fossil fuels produces soot, smoke, and what else?
5. Air pollution primarily causes severe health disorders affecting which human organ?
Unit 4: Air
36
Activity 3: To Find out How Much Oxygen is in the Air
You will need a test tube, some iron filings, cotton wool, a ruler and a trough of water.
Wet the inside of the test tube. Put the iron filings into it. Put some moist cotton wool in the test tube. Turn the tube upside down in a trough of water. Mark the level of the water. Place a ruler alongside the tube and leave it for a week.
Crucial Result: You will see that the water level has risen to 1/5 (20%) of the tube! The iron filings have used up the oxygen in the trapped air to form rust. This proves that oxygen makes up 1/5th of the air!
Interactive Lab 36.1
🧪 7-Day Iron Filings Rusting Time-Lapse
Drag the Day Slider from Day 0 to Day 7 to observe the iron rust and water rise to exactly 1/5th of the tube!
Time Elapsed
Day 0
Water Rise: 0% (Air intact)
Activity 4: Air Moves from High to Low Pressure
You will need a rubber balloon. Blow up the balloon and hold the neck tightly closed. The air inside the balloon is at a higher pressure than the air outside. Release the neck, and the air rushes out of the balloon like a gust of wind.
Balloon is ready to blow wind.
📝 Page 36 Quick Quiz (5 Questions)
Test Your Knowledge
1. In the iron filings experiment, by how much did the water level rise in the test tube after one week?
2. Why did the water rise in the test tube with wet iron filings?
3. What chemical change occurs to iron filings when they react with oxygen and moisture?
4. Why does air rush out violently when you release the neck of an inflated balloon?
5. The rushing air from the released balloon demonstrates how what is created in nature?
Unit 4: Air
37
Summary
The layer of air which surrounds Earth is called the atmosphere.
The gases found in the air are nitrogen, oxygen and carbon dioxide.
The atmosphere has four layers [and the exosphere extending into space].
Air exerts pressure.
Air has weight.
A barometer measures air pressure.
Air pressure is very useful.
Humans pollute the air in many ways.
Exercises
Answer the following questions:
1. What is the atmosphere?
👉 Click to Reveal AnswerThe layer of air which surrounds the Earth is called the atmosphere.
2. What is the percentage of gases found in the atmosphere? Which layer is the most important for living things?
👉 Click to Reveal AnswerNitrogen is about 78% (nearly 4/5), Oxygen is about 21% (1/5), and other gases (argon, carbon dioxide, etc.) make up 1%. The Troposphere is the most important layer for living things because it contains the oxygen needed for breathing and all water vapour.
3. Name the layers of the atmosphere.
👉 Click to Reveal Answer1. Troposphere, 2. Stratosphere, 3. Mesosphere, 4. Thermosphere, and 5. Exosphere.
4. What is atmospheric pressure?
👉 Click to Reveal AnswerThe large mass of air in the atmosphere is heavy and presses down hard on Earth. Scientists call this weight of air the atmospheric pressure.
5. Describe a barometer.
👉 Click to Reveal AnswerA barometer is an instrument used to measure air pressure. A simple barometer consists of a long glass tube sealed at one end, filled with mercury and inverted in a dish containing mercury.
6. How is weather affected by changes in air pressure?
👉 Click to Reveal AnswerAir always moves from areas of high pressure to areas of low pressure. When pressure drops low in an area, high pressure air rushes in, creating windstorms and turbulent weather.
Fill in the blanks to complete the following statements:
(Click on any blank line to reveal or hide the word!)
(a) The atmosphere extends to hundreds of kilometres above Earth's surface.
(b) Air exerts pressure.
(c) The pressure of the atmosphere is measured by a barometer.
(d) A barometer is used to forecast weather.
📝 Page 37 Mastery Quiz (5 Questions)
Summary Check
1. Which gas is identified in the summary as essential for respiration and burning?
2. True or False: Air has weight, which is the direct cause of atmospheric pressure.
3. What scientific tool is used to forecast weather by detecting pressure changes?
4. Which atmospheric layer is situated closest to Earth's surface where weather happens?
5. According to the summary, air pollution is caused by:
Unit 4: Air
38
Exercises (Continued from Page 37)
Fill in the blanks (continued):
(e) Air pressure decreases as we go from sea level to the top of mountain.
(f) We use air pressure to suck liquids through a straw.
(g) A barometer is used to measure air pressure.
3. Choose the best answer:
(Click any option to test yourself. Green = Correct, Red = Wrong!)
(a) Air moves from regions of:
(b) Low pressure causes:
(c) Air pressure decreases from:
(d) A barometer is used to measure:
(e) The top layer of the atmosphere is called:
(f) The normal atmospheric pressure at sea level is equal to the following millimetres of mercury:
(g) The stratosphere layer has a special gas that acts as a protected shield stops harmful rays from reaching the Earth it's called:
(h) A barometer is used to measure the pressure of:
(i) Liquids boil at a lower temperature at:
📝 Page 38 Final Mastery Quiz (5 Questions)
Grand Review
1. Why do liquids boil at a lower temperature at high altitudes?
2. The gas that stops harmful ultraviolet (UV) radiation from reaching Earth is:
3. What is the standard height of mercury supported by air at sea level?
4. Which layer lies at the very top of Earth's atmosphere merging with solar wind?