The properties of air
Ref Ref FAA-H-8083-25C version 2023
Air is fluid
To describe the properties of air, we need to know various key terminology at the beginning
- Viscosity
- Friction
- Pressure
- Density
- Temperature
Viscosity
- “friction” of fluid
- is used to describe the resistance of flowing
- high viscosity means “thick” and resist flowing
- low viscosity means “thin” and flow easily
Friction
- is talking about two objects has different property and so when two objects come into contact, there is a resistance
Pressure
Pressure = Force / Area
Density
Density = Mass/Volume
Temperature
- average kinetic energy (K.E) of the particles in a substance or system, it is a terms of Physic
From about chart, we can see that some of the properties of standard atmosphere. Why?
Why Altitude increase, the pressure drop, temperature drop? (and air density drop, didn’t shown here)?
It is all about physic – back to the basic newton’s law – the newton’s 2nd law:
Force = ma (Force = mg)
Let us use the god view to look at the earth, since the vertical distance increase, the effect of gravity force will decrease, and so the force acting on the air become less)
Pressure = Force / Area
Since the force acting on the air drops, and so the pressure drop
Air density = Mass of air / Volume
Indeed, since the mass of air reduce and so the air density reduce.
In terms of the temperature, we can just use the lapse rate to explain.
