Data Analysis
Planetary Atmospheres
The layer of gases surrounding a planet is known as its atmosphere. All of the planets in our solar system have some form of atmosphere. The weight of an atmosphere creates atmospheric pressure at the planet's surface.
The table at the right gives data about the atmospheric composition and pressure for several of the planets.
Interpreting Tables Which planet listed in the table has the greatest atmospheric pressure?
Interpreting Tables What chemical substance exists in all but one of the atmospheres?
Planetary Atmospheres
Planet
Composition of Atmosphere
Atmospheric Pressure (kPa)
Mercury
Mixture of helium, sodium, and oxygen
10−12
Earth
77% nitrogen, 21% oxygen, 1% argon
101.3
Venus
96% carbon dioxide, 3.5% nitrogen
9120
Mars
95% carbon dioxide, 2.7% nitrogen, 1.6% argon
0.71
Converting Units The bar is another unit of pressure (1 bar = 101.3 kPa). Convert each of the given pressures into bars.
Using Formulas How much force is exerted on a 2.00-square-meter area of Venus's surface?
Predicting On which planet would a heliumfilled balloon have the smallest volume?
Figure 3 This Pascal vase is made up of several oddly shaped vases that are connected to one another at their base.
Drawing Conclusions What can you conclude from the fact that all of the fluid levels are the same?
As you just learned, fluid pressure is determined by the type of fluid and its depth. Thus the amount of fluid, measured in terms of volume or weight, does not affect pressure. To prove this, imagine a large lake and a bathtub. Although they contain very different amounts of water, the pressure at a depth of 25 centimeters is the same in both the lake and the bathtub.
Note that each of the connected vases in Figure 3 contains a different amount of liquid. Yet, the liquid levels are all the same. Why is this? It is because pressure depends on depth, not amount. If the pressure at the bottom of all the vases were not the same, the water would flow until the pressures equalized.
Air Pressure and the Atmosphere
You live at the bottom of a vast ocean of fluid. Unlike fish, however, you live in an ocean of air. Air is a mixture of gases that make up Earth's atmosphere. Just as ocean water exerts pressure, so does Earth's atmosphere. The weight of Earth's atmosphere exerts a pressure of about 101 kPa at sea level.
Just as water pressure in a beaker increases with depth, air pressure increases with the depth of the atmosphere. Instead of saying they are at a certain depth in the atmosphere, however, people refer to their altitude above sea level. 
Air pressure decreases as the altitude increases.
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