Hot Air Balloons and the Mass of Air - DO NOW : #9

Do Now # 9 Does Air Have Mass?  How do we know?








Hot air balloons are based on a very basic scientific principle: warmer air rises in cooler air. Essentially, hot air is lighter than cool air, because it has less mass per unit of volume. A cubic foot of air weighs roughly 28 grams (about an ounce). If you heat that air by 100 degrees F, it weighs about 7 grams less. Therefore, each cubic foot of air contained in a hot air balloon can lift about 7 grams. That's not much, and this is why hot ir balloons are so huge -- to lift 1,000 pounds, you need about 65,000 cubic feet of hot air.

In simple terms, density is the mass of anything - including air - divided by the volume it occupies. In the metric system, which scientists use, we usually measure density in terms of kilograms per cubic meter. The air's density depends on its temperature, its pressure and how much water vapor is in the air. We'll talk about dry air first, which means we'll be concerned only with temperature and pressure

Mass of Air
1.21kg/m³ at 20 deg C at sea level
1.16kg/m³ at at 30 deg C

Read more: http://wiki.answers.com/Q/What_is_the_mass_of_a_cubic_meter_of_air_at_room_temperature#ixzz1XhtdMfjL

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Components in Dry Air

The two most dominant components in dry air are Oxygen and Nitrogen. Oxygen has a 16 atomic unit mass and Nitrogen has a 14 atomic units mass. Since both of these elements are diatomic in air - O₂ and N₂, the molecular mass of Oxygen is 32 and the molecular mass of Nitrogen is 28.
Air is a mixture of gases and the total mass can be estimated by adding the weight of all major components as shown below:

Components in Dry Air	Volume Ratio compared to Dry Air	Molecular Mass - M(kg/kmol)	Molecular Mass in Air
Oxygen	0.2095 = 20.95%	32.00	6.704
Nitrogen	0.7809 = 78.09%	28.02	21.88
Carbon Dioxide	0.0003= .03%	44.01	0.013
Hydrogen	0.0000005= etc	2.02	0
Argon	0.00933	39.94	0.373
Neon	0.000018	20.18	0
Helium	0.000005	4.00	0
Krypton	0.000001	83.8	0
Xenon	0.09 10-6	131.29	0
Total Molecular Mass of Air			28.97