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CHAPTER 13 Forces in Fluids

CHAPTER 13 Forces in Fluids. Physical Science . Fluid and Pressure. Fluid and Pressure 13.1. Pressure – The result of force distributed over an area Pressure = Force(in Newton's – N)/area (m 2 ) Pascal (Pa) – SI unit for Pressure Named after French scientist, Blaise Pascal (1623 – 1662)

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CHAPTER 13 Forces in Fluids

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  1. CHAPTER 13Forces in Fluids Physical Science

  2. Fluid and Pressure

  3. Fluid and Pressure 13.1 • Pressure – The result of force distributed over an area • Pressure = Force(in Newton's – N)/area (m2) • Pascal (Pa) – SI unit for Pressure • Named after French scientist, Blaise Pascal (1623 – 1662) • Pressure in Fluids • Fluid – substance that assumes the shape of its container • Liquid and gas • Depth and type of fluid = 2 factors that affect pressure • As depth increases, pressure increases • Pressure at 25 cm in bathtub and lake are the same • Amount doesn’t affect

  4. Air Pressure and the Atmosphere 13.1 • Weight of Earth atmosphere at sea level = 101kPa • Air pressure increases with depth of atmosphere just like water • AS ALTITUDE INCREASES, AIR PRESSURE DECREASES • Why do your ears pop? • Unbalanced air pressure inside and outside your ear b/c pressure changes more quickly than ears adjust • Pressure equalizes when air passes thru a small tube and you hear a pop • Body is not crushed by atmosphere b/c pressure inside your body balances outside pressure

  5. Forces and Pressure in Fluids 13.2 • Transmitting Pressure in a Fluid 13.2 • Pascal’s Principle • A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the liquid • Hydraulic Systems • Device that uses pressurized fluid acting on pistons of different sizes to change a force • Input force applied to small piston, pushes on fluid of seal system  pushes large piston = output force

  6. Bernoulli’s Principle 13.2 • Daniel Bernoulli (1700 – 1782) • As speed of fluid increases, the pressure within fluid decreases • Blow across the top of a piece of paper, paper lifts upward… WHY? • Pressure is constant below and decreases above • Wings and Lift • Why can a bird and airplane fly • Aerodynamics so air travels faster over the wings • Lift – the pressure difference between the top and bottom of the wing creates and upward force • Birds can flap wings to produce some lift and forward motion • Sometimes do opposite with cars to keep downward force for traction

  7. Buoyancy 13.3 • Buoyant Force • Buoyancy – the ability of a fluid to exert an upward force on an object lace in it • Apparent loss of weight • Water exerts and upward force on object, making easier to lift • Acts in opposite direction of gravity • Water pressure increases with depth SO forces pushing up on bottom are greater than forces pushing down on top

  8. Archimedes’ Principle • Archimedes – Greek mathematician – died 212 B.C. • The buoyant force on an object is equal to the weight of the fluid displaced by the object

  9. Density and Buoyancy 13.3 • Density = mass/volume • g/cm3 • If object less dense than fluid = float • 2 forces always act on an object in a fluid • Weight • Equals force of gravity (mass X 9.8 m/s2) • Acts downward • Buoyant force • Equals weight of volume of displace fluid • Acts upward • When force is equal – object floats or is suspended

  10. Suspended • Same density as the fluid it is submerged in • Buoyancy = weight • Sinking • weight > buoyancy • Floating • Buoyancy > weight • Why does a piece of steel sink and a huge steel ship float? • Ship • Shape of hull • Shaped to displace large volume of water = large buoyant force and it increases volume and decreases density

  11. http://www.teachertube.com/view_video.php?viewkey=cafa030c827d58b2cc85 – 8 minutes http://videos.howstuffworks.com/discovery/6540-mythbusters-lets-talk-buoyancy-video.htm - 3 minutes

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