Density+and+the+Atmosphere

**Density and the Atmosphere**
==== Have you ever wondered why people wear oxygen masks when they go mountain climbing or even sky diving? What are those oxygen masks for? What happens to the amount of breathable air as we increase altitude? These and many other questions can be answered using basic understanding of our planet's vertical motion that includes concepts such as heat, temperature, pressure, temperature scales, composition of the atmosphere, and density. ====

Some important facts to know when studying density and the atmosphere:
====Heat is defined as "transferred thermal energy-- most commonly, the kinetic energy of molecules making up substance, vibrating and bouncing against each other" or in other words, it is the //total// energy of molecules or atoms in a material. Temperature on the other hand is " a measure of substance's ability to transfer heat, rather than the amount of heat transferred" or the //average//==== ==== energy of molecules or atoms in a material. Ex. a match lit under a pot of boiling water reaches a much higher temperature than the water, but it is able to give off much less heat, since only a small amount of thermal energy is created and released by it. Another example is the Arctic Ocean, which has a large amount of heat (because of a large mass) even thought the temperature is low. And another is air in an oven at 500 degrees Fahrenheit has high temperature but little heat yet when you touch anything solid inside the oven you will get burned because the temperature is the same but there is much larger heat transfer present. In simpler terms you can have a large amount of heat but low temperatures and have high temperatures but little heat. ==== ==== So what do heat and temperature have to do with differences in air density? Why is our atmosphere made up of different layers of air and not just one layer? Atmospheric heat and temperature is influenced by pressure. Pressure is defined as "the force per unit area that one region of a gas, liquid, or solid exerts on another." In other words, when molecules bump into one another it can create force on that object or on one another and in the case of our atmosphere's pressure, it is a result of the weight of the entire underlying column of air. Atmospheric pressure is the force of air pressing down on earth. It equals the weight of air directly above that point and it depends on the density ( how tightly packed molecules are) of air. The denser air exerts more air pressure than less dense air does. The most dense layer of air is closest to our planet is the Troposphere layer and the least dense air layer that settles farthest from our planet and is nearest space is called the Thermosphere. ====

**Figure 6 Selected Properties of the Earth's Atmosphere (p. 14 2010 Earth Science Reference Table)**
====So to answer our question earlier as to why mountain climbers and sky divers need oxygen supplies whenever they ascend or descend from higher altitudes...it has to do with the availability of breathable air as air pressure varies as they increase or decrease their elevation. As you increase altitude air pressure becomes less and less. If people go beyond the Troposphere which is about 10 km from sea level and mid way to the Stratosphere, air pressure is already non existent. We have several layers of air and not just one, we know that air varies in density depending on the pressure exerted on the it. To help us remember all the properties and compositions of each of the earth's atmosphere layers here is a cool song that will help you understand the different layers of air that surround our planet.This song is about the layers of the atmosphere sung to the tune of "Put On" by Young Jeezy (featuring Kanye West) by a teacher named Mr. Lee...Enjoy listening to it!==== media type="youtube" key="AkaY1dvZer4?version=3" height="349" width="425"

Fahrenheit- water freezes at 32 F and boils at 212 F
Celsius- water freezes at 0 C and boils at 100 C

**Figure 7 Temperature Scales (page 13 2010 Earth Science Reference Table)**
In converting Celsius/ Centigrade into Fahrenheit in your head, you may just double the Celsius/ Centigrade, subtract the first digit, and add 32. Ex. In converting 37 C to F, 37 + 37= 74; 74- 7 = 67; 67 + 32= 99 therefore 37 C is equivalent to 99 F. In converting Fahrenheit into Celsius/ Centigrade in your head, you must subtract 32, add the first digit, and then divide by 2. Ex. 99 F to C, 99-32=67; 67 + 6= 73; 73 / 2 = 36.5 or when rounded off is 37. It is that simple!


 * Figure 8 Composition of the Atmosphere: **

**Air Pressure and Density**
The structure of the atmosphere is defined by the temperature profile of each of its component layers. The atmosphere does not leave our planet and seep to outer space because it is held to our planet by gravity. Gravity, " the force of attraction that all objects with mass have for each other" is responsible for holding air close to the ground. The weight of the overlying air is the pressure at any point on the surface of our planet. Changes in density drives the vertical motion in our planet's atmosphere and ocean. The less dense (air comprising the Troposphere) rises as it is pushed by more dense air (ex. Mesosphere). The process of displacing less dense air by more dense air holds true for all the rest of the layers of our atmosphere such as the Troposphere and the Stratosphere.

Air density is affected by three major factors namely:

 * 1) ====Temperature- the density of a fluid (gas, or liquid) becomes less when the fluid is heated. Less dense air exerts less air pressure. Places with high temperatures usually have low air pressures than areas with lower temperatures.====
 * 2) ====Water Vapor- (water in gaseous state) At a give pressure point, moist air is less dense than dry air. A water molecule (H2O) has less mass than either a nitrogen or oxygen molecule. Therefore, air with a large amount of water vapor exerts less air pressure than drier air.====
 * 3) ====Elevation- (height) as height increases, air becomes thinner or less dense. Therefore, air pressure becomes less elevation increases.====

**Why do we need to understand density in the atmosphere anyway?**
====Knowing how air molecules behave and how vertical motions (density, pressure, heat etc.) influence it helps us understand how energy is transported, absorbed from the sun, and how it changes the hydrologic cycle (aka water cycle). Without vertical motions happening in the air, there will be no weather pattern whatsoever! No mixing of pollutants in the ground, no rain or any form of precipitation. So believe it or not, density in air matters a lot!====

**Figure 10 Vertical Motion and Temperature**

 * [[image:http://img.ehowcdn.com/article-page-main/ehow/images/a04/va/1l/warm-air-rise-cool-expands_-800x800.jpg width="359" height="354" caption="Rising air cools and expands and eventually creates clouds "]] **

====Now that you have discovered the wonders of how density influences the atmosphere it is time for us to review the vertical motions (density) in the atmosphere through a video. Here is a video about the earth's atmosphere.==== media type="youtube" key="0vcHBNMw2h0?version=3" height="349" width="560"

Earth Science Reference Table (2010). Retrieved from
[] ==== gravity. (n.d.). // The American Heritage® New Dictionary of Cultural Literacy, Third Edition //. Retrieved June 19, 2011, from Dictionary.com website:__ [] __ ====

Lab. Air Pressure (n.d.) Retrieved from
[]

Layer of the Atmosphere (n.d.) Retrieved from
[]

Layer of the Atmosphere Rap by Mr. Lee (n.d.) Retrieved from
[|http://youtu.be/AkaY1dvZer4]

Layers of the Earth's Atmosphere. (2003) World Builders. Retrieved from
[]

pressure. (n.d.). // The American Heritage® Science Dictionary //. Retrieved June 19, 2011, from Dictionary.com website: __ [] __
Pressure and Density. Retrieved from []