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For gases, which are quite compressible, one can apply this equation as long as the density changes are small over the depth considered. In Example 1. Calculating the Mass of a Reservoir from Its Volume , we calculated the mass of water in a large reservoir. We will now consider the pressure and force acting on the dam retaining water. See Figure 2.
The dam is m wide, and the water is Figure 2. The dam must withstand the force exerted against it by the water it retains. This force is small compared with the weight of the water behind the dam. Although this force seems large, it is small compared with the 1. Note that the pressure found in part a is completely independent of the width and length of the lake—it depends only on its average depth at the dam.
In the diagram, the thickness of the dam increases with depth to balance the increasing force due to the increasing pressure depth to balance the increasing force due to the increasing pressure.
Atmospheric pressure is another example of pressure due to the weight of a fluid, in this case due to the weight of air above a given height. However, the average pressure at sea level is given by the standard atmospheric pressure P atm , measured to be.
This relationship means that, on average, at sea level, a column of air above 1. See Figure 3. Figure 3. Atmospheric pressure at sea level averages 1.
Calculate the average density of the atmosphere, given that it extends to an altitude of km. Compare this density with that of air listed in Table 1.
The density of air at sea level is given in Table 1 as 1. Calculate the depth below the surface of water at which the pressure due to the weight of the water equals 1. The atmosphere protects life on earth by shielding it from incoming ultraviolet UV radiation, keeping the planet warm through insulation, and preventing extremes between day and night temperatures.
The sun heats layers of the atmosphere causing it to convect driving air movement and weather patterns around the world.
Teach your students about the Earth's atmosphere with the resources in this collection. A barometer is a tool used to measure atmospheric pressure, also called barometric pressure. An altimeter is a device that measures altitude, the distance of a point above sea level. Students conduct a series of experiments to see how water depth affects pressure. They then develop a model to illustrate how pressure increases in deeper water.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. A barometer measures atmospheric pressure, which is also called barometric pressure. Celsius scale. Fahrenheit scale. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
Last Updated May 14, Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service. Interactives Any interactives on this page can only be played while you are visiting our website. For every 33 feet Many animals that live in the sea have no trouble at all with high pressure.
Whales, for instance, can withstand dramatic pressure changes because their bodies are more flexible. Their ribs are bound by loose, bendable cartilage, which allows the rib cage to collapse at pressures that would easily snap our bones.
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