Air

A colorless, odorless, tasteless, gaseous mixture, mainly of nitrogen and oxygen.

Composition

Explanation

There are many gases that make up the atmosphere, but all the varieties actually make up a small portion of the air. Look below to see the actual percentages of different gasses.

• Nitrogen is the most abundant gas in the atmosphere, making up 78% .
• Oxygen comes next, making up 21% of the atmosphere.
• The rest of the gasses such as carbon dioxide, water vapor, neon, helium, ozone, and krypton make up less than 1 percent of the atmosphere. However, the little bit that we have of these gasses is crucial for life on Earth.

What You'll Need:

• candle
• large glass jar (calibrated if possible)
• eggcup
• shallow dish of water
• matches

Directions

1. Get an adult to help you, or get permission to use candles.
2. Put the candle into the eggcup and fix into place with a little melted wax.
3. Fill the bowl about 3/4 full with water and place the candle in the middle. Make sure the candle is well clear of the surface of the water.
4. Light the candle and let it burn for a couple of minutes.
5. Place the jar over the candle at a slight angle to expel some of the air.
6. Note the level of water in the jar.
7. Watch what happens after a while.

What's Happening?

The candle must use the oxygen to burn, so the air in the jar is being used up. As the candle uses the oxygen, the water rises into the jar to take the place of the oxygen. When the flame goes out, it means all the oxygen is used up. If you look at the water level when the flame is out, you will see it is filled about a fifth, which means that the oxygen made up about a fifth of the original air. If you look at the numbers above in the explanation, you will see that this is true because the oxygen takes up twenty-one percent of the atmosphere.

The atmosphere is arranged in layers. Below is a description of what the atmosphere is made of.

• Troposphere: Meaning "sphere of change," this is the only layer that contains water vapor. This is where weather develops. The air gets colder the farther it is from the earth, and about 6 miles (10 kilometers) up it can be as cold as -58 degrees Fahrenheit (-50 degrees Celsius).
• Stratosphere: This is the layer above the troposphere and is known as the ozone layer. Ozone is a type of oxygen and it traps some of the rays of the sun as they pass through to protect us from the harmful ultraviolet rays. This layer extends from the troposphere to about 30 miles (50 kilometers) above sea level.
• Mesosphere: This cold layer extends from 30 to 50 miles (50 to 80 kilometers) above the surface. It contains a mix of oxygen and nitrogen, but the density of the gases is far too low to support life. Lying above the protective ozone layer, it is also subject to a lot of ultraviolet radiation.
• Thermosphere: Intensely hot, this layer extends from 50 to 250 miles (80 to 400 kilometers) above the surface of the Earth. It is very different than the other layers because ozone, carbon dioxide, and water vapor are virtually nonexistent in this layer, and the overall density is extremely low. The air in this layer is still dense enough, though, to burn up fast-moving meteors. Temperatures range from -130 degrees Fahrenheit (-90 degrees Celsius) at the lowest point to several thousand degrees at the highest point.
• Exosphere: This is the outermost edge of the atmosphere, and it extends from 250 miles (400 km) above the Earth's surface and on into space at around 500 miles (800 kilometers).

Explanation

In 1644, an Italian scientist named Torricelli proved that just like everything else, air has weight. He filled a tube with mercury, turned it upside-down and put it in a bowl of mercury. The mercury in the tube did not run out into the bowl because the weight of the air pressing down prevented the mercury in the bowl from rising. The total weight of all the air around the earth is about 5,000 million million tons. We don't feel any weight of the air because there is an equal force pushing outward from inside our bodies.

The pressure of the air from weight is called air pressure. Air presses in all directions--up, down, and sideways-- and gradually decreases as you go higher in the atmosphere. Aircraft can even measure their altitude by the air pressure because it is so constant. Jet airliners must have pressurized cabins because the pressure drop at high altitudes would make it impossible to breathe.

Look at the experiments below to learn more about air pressure.

What You'll Need:

• smooth-topped stool
• suction cup
• string

Directions:

1. Tie some string to the suction cup.
2. Press the cup to the top of the stool.
3. Lift the cup and see what happens.

What's Happening?

The stool is lifted by the suction cup because there is so much air pressure. When it is pressed against a flat surface, like a stool, air is forced out and the pressure inside is reduced. Since the pressure outside is now much greater, the suction cup is pushed firmly down. There is even enough pressure to hold a stool in the air.

What You'll Need:

• thin metal can with airtight cap
• 1/2 cup of water
• cooker with gas burner

Directions:

1. First get an adult's help on this experiment, or permission to use the stove.
2. Clean the can thoroughly inside and out.
3. Pour a small amount of water into the can.
4. Heat the water gently over a gas flame. DO NOT put the cap on.
5. When the water is boiling and steam is rising from the can, remove it from the heat and place it on a worktop.
6. Now screw the cap firmly, using a cloth to protect your hands. KEEP YOUR FINGERS CLEAR, and watch as the can crumples.

What's Happening?

The can keeps its shape in normal conditions because the air pressure is the same inside and outside the can. When you boil the water, steam is produced which pushes much of the air out of the can. However, the pressure of the steam still equals the air outside. When you put the cap back on, the air stops getting in as the steam cools and condenses too water, creating a partial vacuum. Pressure outside is now much greater than the inside, so it crushes the can.

Explanation

The Swiss mathematician Daniel Bernoulli discovered something in 1738 now called the Bernoulli effect. He found that whenever air moves, its pressure drops. The faster air or liquid moves, the more pressure drops. This is the effect that enables aircraft to fly and sailing ships tosail into the wind. Look at the experiments below to see what happens when air moves (and the pressure lowers).

What You'll Need:

• two Ping Pong balls
• thread
• adhesive tape or glue
• drinking straw

Directions:

1. Glue or tape thread to two Ping Pong balls. If you use tape, use as little as possible.
2. Hang the balls at equal heights about 3/4 inch (2 cm) apart.
3. Now try to force the balls apart by blowing through a drinking straw as hard as you can.

What's Happening?

The harder you blow, the closer the two balls will swing together. This is because when you blow harder, air streams between the balls will get faster. So the pressure there drops and the balls are pushed together by the greater pressure on the outside of each ball. Instead of pushing the balls apart by blowing, you are pushing them together.

What You'll Need:

• one Ping Pong ball
• hairdryer

Directions:

1. Turn on the hairdryer and face it upward (avoid your face, though).
2. Place a Ping Pong ball over the hairdryer, without touching it.
3. The air will take the ball and float it in the middle.

What's Happening?

The air moves fastest in the center of the jet, so the pressure is the lowest there. If the ball ever drifts to one side, it is pushed to the middle again by the higher pressure where the air is slower at the edges of the air stream. This is another example of the Bernoulli effect. Faster air has lower pressure than normal because the air behind is pushing harder so must have higher pressure than the moving air.

Explanation

Since air pressure drops as it flows faster, wings can lift anything into the air because they are cut through the air at a slight angle or are bowed upward. This means that air streaming over the top of the wing goes farther and faster, while air below goes slower. So the air above the wing is at a lower pressure than the air below the wing and the wing is lifted.

Wings only provide a lift when they are slicing quickly through the air. If they move too slowly, the aircraft will fall. Powered aircraft have jets or propellers to thrust them forward and keep them going fast enough. They must go fast enough to overcome the plate's own weight and the drag of the air. So to help with this, planes are made of light materials and streamlined to minimize drag.

Streamline means that the craft is specially shaped so that the air flows smoothly across, while drag is the friction of the air. Look at the experiment below for a demonstration of streamline and drag.

What You'll Need:

• candle
• saucer
• modeling clay
• cardboard
• paper clips
• matches
• friend

Directions:

1. Get an adult to help you with this experiment, or permission to use matches.
2. Place the candle on the saucer and light it.
3. Hold the piece of cardboard flat in front of the candle and have a friend blow through the cardboard toward the candle.
4. Note what happens.
5. Bend the cardboard so the corners meet, but don't crease the fold. Paper clip it together at the open edge.
6. Line the folded cardboard in front of the candle.
7. Have your friend blow toward the candle again.
8. Note what happens.

What's Happening?

In the first case, with the flat piece of cardboard, the candle bends toward the candle, while in the second case the candle bends away from the cardboard. The first case is the shape of a drag, and the second is the shape of a streamline. Airplanes, as well as fast cars and birds, are shaped in the streamlined fashion. The air is supposed to go smoothly as possible, so there isn't as much of a drag. The experiment above shows how little the candle is disturbed by the streamline shape.

Explanation

Along with the gasses in the atmosphere, there are many particles of dust and pollutants. This pollution is put into the air by humans, through industry, plants, automobiles, airplanes, and other activities of work and play. Cars and trucks, for example, push solid particles of soot into the air along with poisonous gases such as nitrogen dioxide and carbon monoxide. This causes illness and foggy weather, and may later cause something disastrous.

We've already decreased the ozone layer through our activities. By using man-made chlorofluorocarbon gases (CFCs), we have caused small holes to appear in the ozone layer. This is the layer that protects us from the sun's ultraviolet rays, and we need the ozone layer to sustain life. Even small holes will hurt people through sunburn and skin cancer. CFCs are used in many aerosol sprays, like those for cleaning electronic circuits. CFCs are also found inside refrigerators. They are extremely hard to break down chemically, but high in the atmosphere the sunlight makes them release chlorine, which combines with oxygen atoms in the ozone and destroys it.

Explanation

Air pressure changes with atmospheric conditions, so we can use it to determine what the weather will be like. Air pressure is measured in millibars, or mb for short, using a barometer. A barometer measures air pressure and is a good indicator of the weather. You can make your own barometer by doing the experiment below.

What You'll Need:

• glass
• balloon
• rubber bands
• adhesive tape
• drinking straw
• wood base
• card
• ruler
• scissors

Directions:

1. Cut the neck off the balloon with the scissors. Stretch the body of the balloon tightly over the glass and secure it with rubber bands.
2. Cut one end of the drinking straw into a point.
3. Attach the other end of the straw to the middle of the balloon using tape.
4. Fix the glass to the wooden base with adhesive tape.
5. Fold the card at the bottom to make a tab.
6. Attach the card to the wooden base so that the point of the straw touches the card.
7. Mark where the straw points to each day to record changes in air pressure.

What's Happening?

When the air pressure drops, air inside the jar pushes the balloon up and makes the straw go down. When air pressure rises, the air in the jar goes down and the straw goes up. When the pressure falls, it usually means a storm is on the way. You can see when the air pressure goes up and down by placing your barometer somewhere out of the sun. However, it only gives a rough guide because it also responds to air temperature. For accurate readings, you need a professional barometer.