pressure ch3

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  • 1. Forces In Fluids Fluid Pressure Hydraulic Devices Pressure and Gravity Buoyancy Fluids in Motion

2. Fluid Pressure Pressure is defined as the force thatparticles exert over a certain area dueto their weight and motion. Pressure=Force/Area N/cm2 Fluids move from areas of higherpressure to areas of lower pressure. All liquids and gases are fluids. 3. Pressure (continued) 4. Pressure (continued) 5. Pressure (continued) 6. Pressure (continued) 7. Pressure (continued)A BThe greater the density of gas particles, thegreater the pressure they exert. 8. Hydraulic Devices Pressure in a fluid is the samethroughout and is exerted equally in alldirections when there are no outsideforces acting on the fluid. Hydraulic devices are machines thattake advantage of the fact that pressureis transmitted equally in all directions ina liquid. 9. Hydraulic Devices (continued) Hydraulic devices apply small force to asmall area to develop a large net forceover a larger area. Examples include car brakes, barbershop chairs, and snow plows. 10. Hydraulic Devices (continued) 11. Examples of hydraulic devices 12. Pressure and Gravity Due to the force of gravity the pressureof any fluid increases with depth. Air pressure decreases as altitudeincreases. This is called an inverserelationship. 13. Pressure and Gravity(continued) 14. Pressure and Gravity(continued) 15. Buoyancy Buoyancy is defined as the upwards force in a fluid which acts opposite of gravity. The buoyant force on an object is equal to the weight of the fluid displaced by the object. This concept is known as Archimedes Principle. 16. Buoyancy (continued) Archimedes and the Case of the Golden Crown In the first century BC, a Roman architect named Vitruvius told a story of how Archimedes uncovered a fraud in the making of a golden crown made for Hiero II, the king of Syracuse. Suspecting that the goldsmith might have replaced some of the gold given to him with an equal weight of other, less valuable metals, Hiero asked Archimedes to determine whether the crown was pure gold. Since the crown was considered a holy object dedicated to the gods, Archimedes could not disturb or destroy the crown in any way. To determine what the crown was made out of, Archimedes knew that he would need to work out the volume of an irregular solid. He thought about this for many days, but he had trouble thinking of a reliable way to approach this dilemma. The solution finally occurred to him when he was visiting the public baths. When he stepped into the water he noticed how the water overflowed the sides of the bath. He realized that the volume of the spilt water was equal to his bulk. He now knew how to find the volume of an irregularly shaped object like a human body or a kings crown! Archimedes jumped out the bath and ran naked through the streets of Syracuse shouting Eureka, eureka! 17. Buoyancy (continued) 18. Buoyancy (continued) An object floats when it displaces avolume of fluid whose weight is greaterthan or equal to its own weight. Density is the ratio of the mass of asubstance to its volume. Density= Mass/Volume g/cm3 or g/ml An object is neutrally buoyant if itsweight and buoyant force are equal. 19. Buoyancy (continued) An object will float in a fluid if its densityis less than the density of the fluid. Water has a density of 1g/cm3. The densities of most woods vary from .3 to .9g/cm3. Gold has a density of 19.3g/cm3. 20. Buoyancy (continued) 21. Buoyancy (continued) 22. Buoyancy (continued) 23. Bernoullis Principle Bernoullis Principle explains that thepressure in a moving stream of fluid isless than the pressure in thesurrounding fluid. The faster a fluid moves, the lesspressure it exerts. This is the reason airplanes can fly. 24. Bernoullis Principle