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Gas Behavior - molecules in every cubic centimeter moving...

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Gas Behavior Now that we have seen what determines if a planet has an atmosphere or not, let's look at how atmospheres behave and how they affect the conditions on the surface of a planet. Only three things are needed to describe how a gas will behave: temperature, pressure, and density. Temperature and density have already been discussed, although for gases it is usually easier to use "number density" as in "number of particles per volume" instead of the usual mass density. Let's take a closer look at pressure. Pressure Pressure is the amount of force exerted on a surface per unit area such as a number of newtons per square meter (or pounds of force per square inch). In the metric system, the unit of pressure is the pascal (Pa) . This pressure is supplied by all of the particles in an atmosphere colliding into each other. At the Earth's surface there are approximately 25 million trillion (2.5 x 10 19 )
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Unformatted text preview: molecules in every cubic centimeter moving about at speeds of hundreds of meters per second , so yes, they are going to bump into each other! At the Earth's surface at sea level there is about 100 kilopascals of pressure exerted all over your body. For planet atmospheres, scientists will usually use a unit called a " bar " equal to 100 kilopascals, so the Earth's surface pressure at sea level is about 1 bar. That pressure is equivalent to about 1 kilogram pressing down in one Earth gravity on every square centimeter. If an adult pinky is about 1 centimeter in width (more or less), your body has quite a lot of square centimeters of surface area. So why do you not feel all that weight pushing you down at the Earth's surface? As described in the figure below, the air pressure pushes in all directions equally and the pressure of the fluid in your body pushing outward balances the air pressure....
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