How to measure the density of air? How much does air weigh per cubic meter? What is the average density of air?
The density of air varies depending on temperature and pressure. Air at sea level will weigh more depending on a number of factors. At higher altitudes, the air becomes thinner because of lower atmospheric pressure. This means that the amount of air increases as altitude rises.
You can calculate the density of air using the formula Density Mass / Volume. If you want to know the mass of air, multiply its volume by its density. For example, if you want to know the density of air at sea level, divide the mass of air by its volume.
Confused by what all of these words mean, but need to know how to find the density of the air due to your ambition to become a pilot? Don’t worry – we’re about to explain it all to you.
What Do We Mean By Air Density?
The density of air refers to the weight of one unit of air compared with another unit of air. In other words, it’s the ratio between the mass of an object and the volume occupied by that object. Dry air is made up of mainly nitrogen and oxygen.
Nitrogen takes up around 78% of air while oxygen takes up around 21%. The last 1% is made up of many different gasses mixed together.
As you can see, the air around us is a mixture of many different gasses. This means that there is no constant density, as the density will depend on the current composition of the air. For example, the more water vapor in the air, the lower the density will be.
What Is Air Density At Sea Level?
At sea level, the average density of dry air is around 0.0765 lb/cu ft (1.225 kg/m³), assuming that the sea level is at 59 degrees Fahrenheit with a PSI of 14.7. However, once you change the humidity, temperature, and altitude, the density of the air will change.
For every 1000ft of change in altitude, you can expect to see a change of 0.0022-0.0023 lb/cu ft (0.035-0.036 kg/m³) in the air density.
Information Needed To Work Out The Air Density
To work out the density of the air, you’re going to need some information to use within the equation. Here’s what you’re going to need to figure out before you can use the air density equation.
Air Temperature
For this calculation, you’ll need to know the temperature of the air. You could use an online thermometer or just take a guess based on the weather outside. It should be somewhere in the range of 10°C to 30°C.
Air Pressure
This is also known as the barometric pressure. You can either use an online calculator or simply look up the pressure for your location on Google Maps. The pressure should be somewhere in the region of 1013 hPa.
Dew Point
If you don’t have access to a dew point meter, then you can use an online calculator to find the dew point from the temperature and pressure. Dew point is the term for when the water vapor begins to condensate.
Make sure that you have found the dew point in degrees Celsius rather than Fahrenheit.
Equation To Work Out Air Density
It’s surprisingly easy to find the air density once you have found the information that we have mentioned above. All you need to do is divide the air pressure by the pressures of the dry air and the water vapor.
Still don’t get it? Let’s break it down for you:
1. Work Out The Saturation Vapor Pressure
Use the following formula to do this:
p₁ = 6.1078 * 10^[7.5*T /(T + 237.3)]
Use this formula where T is measured in celsius. The saturation vapor pressure will be at 100% of the relative humidity.
2. Use This To Find The Actual Vapor Pressure
Multiply the saturation vapor pressure by the relative humidity by using this equation:
pv = p₁ * RH
3. Remove The Vapor Pressure From The Total Air Pressure
Use the following equation to determine the pressure of the dry air:
pd = p – pv
4. Use All Of Your Findings In One Final Formula
Use this equation with all of the new data within it:
ρ = (pd / (Rd * T)) + (pv / (Rv * T))
Where:
pd: pressure of dry air in Pa
pv: water vapor pressure in Pa
T: temperature in Kelvins
Rd: Gas constant in dry air equating to 287.058 J/(kg:K)
Rv: Gas constant for water vapor equating to 461.495 J/(kg:K)
Still Confused?
You might be confused by the information that we have mentioned above, as it seems like working out the air density is much more difficult now than when you learned about it at school. This is because the air density equation taught in schools is:
p = mass of the air / volume
This isn’t incorrect, but the equation that we have mentioned earlier creates a more accurate reading than the simple equation that you were taught in school.
Why Do You Need To Work Out The Air Density?
The reason why you need to calculate the air density is so that you can accurately measure the amount of oxygen that you are breathing in. Oxygen is one of the most important elements that you need to survive. Without enough oxygen, you will die very quickly.
Another reason why you might need to work out the air density is because your job requires you to know this information. Pilots and sailors are common job types that need to be able to work out the air density to know how to control their vehicle better.
Summary
Hopefully, you understand how to work out the air pressure and density. If not, then I recommend that you read through the article again until you fully understand what each of these terms mean. Once you have done this, you will be ready to start calculating the air density yourself!
I decided to create this source of knowledge from my own experiences, in the hopes of helping budding pilots to get through their training.
So, if you’re thinking about becoming a pilot or are in the middle of your training, I hope that this website and my knowledge comes of some benefit to you. I’d love to think that my website made your experience a little less stressful and a lot more fun!
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