Objectives
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Describe the characteristics of air.
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Explain how air pressure works.
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Discuss how air pressure affects our daily lives.
Materials
Background
We are constantly surrounded by lots of tiny and invisible air particles. We often think of air as being something light and weightless. In reality, air is a gas that takes up space and has mass (weight). Since there is a lot of “empty” space between air molecules, air can be compressed to fit in a smaller volume.
Air not only has mass, but exerts pressure as well. The particles of air push in all directions and the force that is exerted is called air pressure.
While air pressure can refer to the pressure of air within a confined area (car tire or football), atmospheric pressure specifically refers to the air pressure exerted by the air molecules above a given point in the Earth’s atmosphere. The closer we get to the Earth, the higher the atmospheric pressure due to the weight of air particles above. This is why there is less air pressure at the top of a mountain than at sea level. The weight of air above compresses the air particles near the surface of the Earth, creating a higher density of particles. The tool used to measure atmospheric pressure is called a barometer. You cannot use a barometer to measure the air pressure inside a tire, a football, or an air mattress.
When we jump into a pool, we feel the weight of the water pressing down on us from all directions. This force is known as water pressure. The deeper you sink, the more pressure you will feel. This is because you have the weight of the water on top of you trying to compress you.
To help us visualize air pressure, imagine that we’re living at the bottom of an ocean of air. At sea level, the air pressure is greater than on the top of a mountain since you have the weight of more air pushing down on you.
How heavy is that air?
A cube of air 1 metre per side has a mass of 1 kilogram. The Earth’s atmosphere is about 480 kilometres thick. This means that on the surface of the Earth, we have 480 kilometres of air pushing down on us. That’s 1,700 kilograms on each of our heads (which is roughly the equivalent of the weight of a male hippopotamus!).
So why don’t we get flattened by all that air pressure?
We have air and fluids inside your body that exert a pressure outward, cancelling out the atmospheric pressure around us. This ensures that our bodies do not collapse under the weight of the air around us.
One of the most important concepts to remember in this unit is that air always flows from a place with high pressure to a place with low pressure. Air will perform amazing feats to get from a high-pressure region to a low-pressure region, including pushing and lifting things in its way. Air flowing from a high-pressure region to a low-pressure region is often felt as wind.
To help students remember the direction of airflow, they can use the phrase “winds blow from high to low.”
In these activities, students will discover how changes in air pressure contribute to many different things, including weather patterns, our respiratory system, and the lift required by airplanes.
Vocabulary
Air pressure – The force of air particles against a surface.
Atmospheric pressure – The air pressure of the Earth’s atmosphere by the air above a given point.
Bernoulli’s principle – The faster a fluid (air) flows, the less pressure it creates.
Compression – To squeeze together.
Density – The mass per unit volume (or the number of air particles in a particular location).
Diaphragm – A thin, circular sheet of muscle below the ribcage that contracts and expands to increase and decrease the volume in the chest cavity.
Exhalation – The removal of air from the lungs.
Expansion – To spread out.
Force – A push or pull that can cause an object with mass to change its velocity, direction, or shape.
Inhalation – The intake of air into the lungs.
Lift – The upward motion generated under the wings as a plane moves forward.
Respiratory system – The part of our bodies that allow us to breathe (consisting of lungs, airways, and muscles).
Volume – The amount of space occupied by a substance.
Wind – The flow of air from a high pressure system to a low pressure system.
Other Resources
NASA | 10 Interesting Things About Air
Science World | YouTube | The Air Show
How Stuff Works | Ears and Diving
Science Kids at Home | Air pressure and Temperature
Kids Science Experiments | Air Pressure
NASA | What makes a plane go up?
Smithsonian National Air and Space Museum | How things Fly
