# Air and Aerodynamics - Grade 6

Air and Aerodynamics Topic A 6.5.1 Provide evidence that air takes up space and exerts pressure, and identify examples of these properties in everyday applications. Properties of Air Air takes up space

Air exerts pressure Air has mass and density Properties of Air Air has many properties.

It It It It It is invisible

is made up of gases takes up space has mass exerts pressure You know air is everywhere because living things need it to survive. You cannot see air, but you can sometimes hear it and feel it.

Air takes up space Think about basketballs, footballs, soccer balls, hot-air balloons, tires and balloons. It is the space the air takes up that gives these objects their shapes. You have a good idea of how much space the air is occupying by the size of the object. When you blow into a balloon, the air entering the balloon

causes it to inflate. The air you are putting into the balloon requires space and causes the balloon to expand and change shape. This clearly demonstrates that air takes up space. Air exerts pressure Because the air pressure on the inside of the balloon is the same as the air pressure on the outside of the balloon, the balloon keeps a constant shape.

If the air pressure on the inside were greater than the air pressure on the outside of the balloon, the balloon would burst. If the air pressure on the outside were greater than the air pressure on the inside of the balloon, the balloon would collapse. Air has mass Pioneering scientists discovered atmospheric

pressure in the seventeenth century and determined a startling new fact: air actually has weight. Air pressure is the force exerted on an object by the weight of tiny particles of air. Atmospheric Pressure Atmospheric pressure is Earths gravitational field pulling on air.

Almost all the gases that make up air are attracted to Earth by gravity. The air that surrounds Earth is being pulled down toward the surface of the Earth. Earths atmosphere is pressing against your whole body. For each square centimetre of your body, there is one kilogram of air pressing on you.

Why are you not crushed by all that pressure? Human bodies are designed to handle a certain amount of air pressure. Remember that you also have air inside your body. That air pressure balances out the pressure that is pushing on you from the outside. Therefore, the air pressure is the same inside and outside your body.

Air has mass and density Mass is defined as the amount of matter in an object. All matter is made up of molecules. Density refers to how tightly or how loosely packed the molecules of an object are. Density is determined by dividing the mass of an object by its volume. You know that some objects are heavier than other objects, even

if they are the same size. An empty bottle and a bottle full of water are the same size, but the bottle full of water is heavier. Water is more dense than air because molecules of water are closer together than molecules of air. Air exerts pressure Because air has density and mass, it exerts pressure.

At sea level, air is densest and exerts the most air pressure. Air pressure decreases the higher you go above sea level because the air becomes less dense. When you climb to high altitudes where the air is less dense and the air pressure is reduced, you begin to pant and puff, trying to get enough oxygen into your lungs.

Oxygen As air pressure decreases, oxygen continues to make up about 21% of the gases in the air, as it does at sea level. However, there is less oxygen available because there is less of all of the airs gases at high altitudes. Airplanes use pressurized cabins to overcome the effects of lower air pressure and density at high altitudes. 6.5.2 Provide evidence that air is a fluid and is capable of

being compressed, and identify examples of these properties in everyday applications. Air is a fluid, can expand and contract, and can be compressed Every object on Earth or in space can be classified as a solid, a liquid or a gas. Air is a fluid. A fluid can be a liquid or a gas.

The molecules in a fluid are not fixed. This means that the molecules are not set in place. The molecules can move around and slide over each other. Fluids Fluids can be poured. They take the shape of whatever container they are put into.

Fluids also tend to flow easily past rounded shapes. Fluids flow from areas of high pressure (high density) to lower pressure (less dense) areas. Changes to Temperature or Pressure When pressure or temperature changes in a fluid, its density changes. Molecules get closer together or farther apart. When air is heated, it expands because the molecules

that make up air start to move faster and take up more space. The farther apart the molecules are, the less dense the air becomes. Changes to Temperature When air gets cold, it contracts. As air cools, its molecules settle closer together and the density increases.

Warm air rises because it is less dense than the cool air surrounding it. Compressed Air Some matter, like air, can be compressed (squeezed) into a smaller space by forcing the molecules closer together than they would normally be. Since the molecules that make up gases are far apart, they can be compressed using pressure.

It is possible to compress air to higher pressures. When you put air into your car tires, it is forced, or squeezed, in a confined space. It is compressed. The molecules of the compressed air inside the tire push on the tire wall, preventing the tire from going flat. What is compressed air used for? Compressed air is used for many things in the world.

Compressed air is used for: Aerosol spray cans

Sports balls Vehicle tires Machines Scuba tanks For generating power for tools 6.5.3 Describe and demonstrate instances in which air movement across a surface results in lift Bernoullis principle.

Bernoullis Principle Bernoulli Daniel Bernoulli was a Swiss scientist of the eighteenth century. His experiments with water flowing through pipes showed that as the speed of water increased, the water pressure decreased.

Other experiments showed that this was true for all liquids and gases. Bernoullis Principle Bernoullis principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases. Bernoullis Principle

Bernoullis principle was a key idea in the development of human flight. Aircraft wings are designed so that air flows over the top of the wing faster than it flows under the wing. This causes the air pressure on top of the wing to be lower. The comparatively higher air pressure underneath the wing pushes the airplane up and creates lift. Lift is an upward force that acts against the force of

gravity. 6.5.4 Recognize that in order for devices or living things to fly, they must have sufficient lift to overcome the downward force of gravity. Forces of Flight Forces of Flight

The following four forces affect flying objects, such as aircraft, birds, and insects, while they are in flight: Lift Thrust

Drag Gravity Lift Lift is the upward force that keeps a flying object in the air. Hot air balloons lift off the ground because the hot air in the balloon is less dense than the cool air that surrounds it.

Airplanes get lift from their wings. Thrust The force that gives a flying object a forward motion. The engines on an aircraft give it the thrust needed for flight. Drag Drag is the force that acts to slow down an object as it

moves through the air. Today, airplanes and other vehicles are designed with smooth lines to cut through the air and overcome drag. Gravity Gravity is the force that pulls objects down toward the ground. The more mass an object has, the greater the gravitational pull on the object.

For this reason, flying objects are often made of less dense materials, such as aluminum and plastic. Example - Airplanes For example, think of an airplane in flight. If the planes lift is greater than its mass, the plane goes up to a higher altitude. It will ascend, or climb, in the air. If the lift decreases, the plane goes down to a lower

altitude. When lift and mass are equal, the aircraft will maintain a level flight. Opposites Thrust and drag also oppose each other. If thrust is greater than drag, the plane moves forward. If the thrust is increased, the plane moves forward faster.

If drag is increased or thrust is decreased, the plane slows down. When thrust and drag are balanced, the plane moves forward at a steady rate. Out of Balance Lift, gravity, thrust and drag each play a part in keeping an aircraft in flight. However, at some points during a flight, some of these

forces may not be in balance. For example, lift and gravity can be unbalanced. Thrust and drag can also be unbalanced. 3, 2, 1 Takeoff! For an airplane to take off, thrust and lift must be greater than drag and gravity. To lower a plane and allow it to land, lift and thrust must be decreased until drag and gravity become greater.

If the plane is headed into the wind, the plane will often be late landing because the force of drag is stronger than expected. A plane can also arrive early if the wind is pushing it from behind. In this case, the force of thrust is helping the plane move forward faster. If all four forces are in balance, an aircraft can hover in place. 6.5.5. Identify adaptations that enable birds and insects

to fly. Adaptations An adaptation is a device or mechanism that changes to become suitable to a new situation. A number of adaptations combine to allow birds and insects to fly. By Design

Most bird species are expertly designed for flight. Some birds, such as hawks, are able to soar. Other birds, like geese, have adapted so that they can fly long distances. Other birds, such as hummingbirds, are able to fly swiftly. Special Adaptations for Birds Birds have special adaptations to achieve flight.

Some adaptations that birds have for flight are: Feathers Powerful flight muscles

Air sacs Hollow bones wings Feathers Feathers give birds a smooth, streamlined shape that reduces drag and maintains body temperature. Tail feathers are used to steer the bird in flight.

Muscles Bird muscles are designed to be strong and to provide sufficient power for flight. The muscles for the wings are designed so they do not tire quickly. To power the flight muscles, birds need a large, constant supply of oxygen. Other Features

Air sacs in a birds thorax and abdomen fill up with air and provide its body with the oxygen needed during flight. The hollow bones of a bird help reduce its weight. Shape of the Wings The shape of a birds wings allows the bird to achieve lift. The wings are curved on top and flat on the bottom.

Air travels over the top of the wing and creates a difference in pressure. As the bird flaps its wings, thrust is achieved on the downward stroke. Insect Wings Insect wings are made up of a thin membrane supported by blood-filled veins. Most insects rely on two pairs of wings that join or

overlap so that they work together as a single pair. Insect wings are one of natures lightest structures, lacking bone and muscle. They are made of chitin, an extremely tough material that is also part of an insects hard outer skin. Wing Support A network of veins gives insect wings extra support. Insect wings are curved on top and flat on the bottom.

Air rushing over the wing has to travel farther because of the curvature, so this air moves faster than air below the wing. Since fast-moving air exerts less pressure than slowmoving air, the difference creates lift. Each downward wing flap creates thrust, propelling the insect forward. How do insects flap their wings? Large-bodied insects lift off by flapping their wings very

rapidly. Insect wings do not just flap up and down. On the upstroke, insect wings move in a figure-eight motion. As the insect wing nears the end of a forward stroke, the wing rotates backward, twisting upside down, parallel to the ground. This rotation speeds up the flow of air over the wing.

Insect Muscles? Insects also have specially designed muscles to power their wings. These muscles are found in the insects thorax. Insects are cold-blooded. This means that they have to be warm before their muscles will work. As it gets cold outside, insects are not able to keep their flight muscles warm, and they are unable to fly.

6.5.6 Describe the means of propulsion for flying animals and for aircraft. Propulsion In order for birds and insects to fly, they must create lift. They must also generate enough propulsion to create thrust. Thrust is the act of an object moving forward.

Propulsion is what gives the object the force to move forward. How do flying animals generate propulsion? Propulsion for flying animals is generated by the flapping of their wings. Propulsion for aircraft is generated by either propellers or a jet engine.

A propeller has a twisted wing shape. A motor or engine turns the propellers so that they push air back toward the body of the airplane. The backward push results in a forward motion of the airplane. Jet Engines The jet engine generates propulsion through the burning of fuel, which creates hot gases.

When the fuel is ignited, the hot gases push out the back of the engine, and the airplane moves forward. 6.5.7 Recognize that streamlining reduces drag, and predict the effects of specific design changes on the drag of a model aircraft or aircraft components. How Streamlining Reduces Drag Drag is the force that acts to slow down an object as it

moves through a gas or liquid. The larger the surface area of an object, the more drag the object has. A crumpled piece of paper falls to the floor faster than a flat sheet of paper because the flat piece has a larger surface area that results in more drag. Today, many manufacturers design objects to have a smooth, streamlined shape to reduce drag. Aircraft are designed to overcome drag.

6.5.8 Recognize that air is composed of different gases, and identify evidence for different gases. Example evidence might include: effects on flames, the using up of a particular gas by burning or rusting, animal needs for air exchange. Gases in the Air Air is a mixture of gases.

Air is made up of: 78% nitrogen 21% oxygen 1% argon

As well as traces of: Water vapour Carbon dioxide Various other components Air Normally, air is a mixture of colourless, odourless, tasteless, and mostly non-metal gases. It is a constituent of all living tissues.

Oxygen Oxygen is needed for combustion and oxidation. Oxidation is the combination of a substance with oxygen. Certain substances have a reaction with oxygen. If a peeled apple is left exposed to the air, it turns brown. The brown colour is the result of the apple reacting to

the oxygen in the air surrounding it. Rust Iron also reacts with oxygen. This is why vehicles rust. Rusting demonstrates the process of oxidation. Combustion Oxygen is also necessary for burning.

Combustion is also an oxidation process. If a candle is lit and left to burn in a closed-in space, it will only burn as long as there is oxygen inside the closed-in space. Once the oxygen in the air is used up, the candle will no longer burn. Carbon Dioxide Carbon dioxide tends to sink because it is heavier than

most gases in the air. It is used to extinguish fires. Carbon dioxide flows over flames and pushes the oxygenated air away. Without oxygen, the fire cannot burn. Air in Nature Plants absorb carbon dioxide during photosynthesis to construct carbohydrates.

Oxygen is released by plants during photosynthesis. Carbon dioxide is present in Earths atmosphere at a low concentration and acts as a greenhouse gas. Greenhouse gases are gaseous components of the atmosphere that contribute to the greenhouse effect. The greenhouse effect is the process by which the atmosphere warms the earth.

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