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Fluids Pressure and Density ● Gas- molecules are free and interacting, and are considered fluids ○ Compressible- a consequence of empty space between molecules ● Liquids- molecules are bonded weakly and slide past each other ○ Incompressible and takes the shape of the container Density ● Liquids are characterized by their density ○ 3 ● Units are kg/m ● Since liquids occupy a volume it is important to remember how to convert a volume. 3 Remember that volumes should be in m basic SI unit. Pressure ● Pressure is most easily defined as force per unit area ○ P=F/A ● Atmospheric Pressure ○ ● Since atmospheric pressure acts uniformly in all directions, we don’t usually notice it. Therefore, if you want to, say, add air to your tires to the manufacturer’s specification, you are not interested in the total pressure. What you are interested in is the gauge pressure – how much more pressure is there in the tire than in the Atmosphere ○ ● Pressure is the same at the same depth. ○ P=P 0ρg h ○ Pressure = atmospheric pressure +gravity*density of fluid*height Pascal’s Principle ● Any change in pressure at any point in a fluid is transmitted to every other point in the fluid. Archimedes’ Principle ● Any body completely or partially submerged in a fluid is buoyed up by a force whose magnitude is equal to the weight