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Forces in Fluids

Forces in Fluids. What is pressure?. The result of a force acting over a given area. Pressure = Force/Area What label? N/m 2 1 N/m 2 is known as a pascal (Pa). Blaise Pascal. 1623-1662 French physicist and mathematician Performed some of the first experiments dealing with pressure.

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Forces in Fluids

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  1. Forces in Fluids

  2. What is pressure? • The result of a force acting over a given area. • Pressure = Force/Area • What label? • N/m2 • 1 N/m2 is known as a pascal (Pa)

  3. Blaise Pascal • 1623-1662 • French physicist and mathematician • Performed some of the first experiments dealing with pressure

  4. The force should be in newtons (N). The area should be in square meters (m2). The resulting unit would be N/m2. One N/m2 is a pascal (Pa). The SI unit of pressure is the pascal. 13.1 Pressure

  5. 13.1 Fluid Pressure • Pressure: is the force per unit area. • A seat that reduces pressure will be more comfortable than a chair with higher pressure. • How can you reduce pressure on a chair?

  6. To calculate pressure, divide the force by the area over which the force acts. 13.1 Pressure • P = F / A

  7. Deeper the more pressure. Weight of water (and air) above pushing against you. Twice weight, twice pressure. Pressure of air above transmitted down through water and adds pressure. Pressure in Liquids

  8. Liquid pressure = weight density x depth. Pressure does not depend on amount of liquid, just the depth. Density and Depth

  9. Pressure exerted by a liquid is the same at any given depth below surface no matter what its shape. Exerted equally in all directions. Density and Depth

  10. Pressure on Dams Liquid Pressure = Weight density x depth

  11. Pressure Increases with Depth

  12. Pressure Increases with Depth • Why are the metal bands round the water tower closer together at the bottom?

  13. Air Pressure • Air pressure at sea level is approx. 101 kPa. • Air pressure will decrease with increases in altitude. • Examples: flying in a plane, driving in the mountains

  14. Air Pressure & the Atmosphere • Just as water pressure increases with depth the weight of the atmosphere results in air pressure. • Air pressure decreases as the altitude increases.

  15. Air pressure • Air pressure is equal to the weight (per unit area) of the column of air extending above that location to the top of the atmosphere.

  16. "Standard Pressure" • 1 atmosphere (at sea-level) * 1 atm = 101.3 kPa = 14.7 psi • kPa is kiloPascals.

  17. Air Pressure & the Atmosphere • Your ears pop when you go up a hill because the pressure changes. • Pressure inside our bodies equal surrounding air • Pressure inside a balloon is equal to the pressure of the surrounding air

  18. 13.2 Forces and Pressure in Fluids • Pressure is exerted equally in all directions. • Pascal’s Principle states that: a change in pressure at any point in a fluid is transmitted equally and unchanged in all directions.

  19. Pascal’s Principle

  20. Pascal’s Principle • A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid

  21. hydraulics • Uses Pascal’s principle and moving pistons with an enclosed pressurized fluid: • Examples: • Car brakes, jacks, and loaders

  22. Hydraulic Systems • Hydraulics is the science of applying Pascal’s principle. • Hydraulic systems use pressurized fluid acting on a piston to change the force.

  23. Hydraulic Systems

  24. When the speed of a fluid increases, pressure in the fluid decreases. Bernoulli’s Principle

  25. Why is wing shaped the way it is? Fast air! Low pressure. Slow air! High pressure.

  26. Bernoulli's Principle is an example of an inverse relationship. An inverse relationship means that when one value goes down, the other one goes up. Bernoulli’s principle

  27. Other applications of Bernoulli’s principle:

  28. Applications of Bernoulli’s principle “OOOh” B-58 Husler

  29. Applications of Bernoulli’s principle “OOOh” B-58 Husler

  30. Applications of Bernoulli’s principle “Go IRL”

  31. Applications of Bernoulli’s principle “Go John”

  32. Applications of Bernoulli’s principle HAIRDRYER AND PING PONG BALL

  33. Applications of Bernoulli’s principle Air

  34. Applications of Bernoulli’s principle

  35. A Hose-End Sprayer

  36. Pressure in straw You reduce air pressure in straw Atmospheric pressure pushes liquid into reduced pressure region Straw Pressure

  37. Interest Grabber What Makes Objects Float and Sink? Do heavy objects always sink when placed in water?

  38. Interest Grabber What Makes Objects Float and Sink? Consider a dime and a large cruise ship. When placed in water the dime quickly sinks, while the cruise ship floats. 1. Which object is heavier, the cruise ship or the dime?

  39. Interest Grabber What Makes Objects Float and Sink? Consider a dime and a large cruise ship. When placed in water the dime quickly sinks, while the cruise ship floats. 2.Knowing that weight acts downward, what can you infer about other forces acting on a floating object?

  40. 13.3 Buoyancy • Buoyancy is the ability of a fluid to exert an upward force on an object placed in it. • Buoyancy causes the apparent loss of weight when an object is placed in a fluid.

  41. Buoyant Force • The pressure on the bottom of the ball is greater than the pressure on the top. • This produces the buoyant force.

  42. 4.9 N 4.3 N 0.6 N 13.3 Buoyancy in a Liquid • Buoyancy • The apparent loss of weight of submerged objects. • 4.9 N object in air. • 4.3 N object in water. • Buoyant force = 0.6 N

  43. Buoyant force- a consequence of pressure increasing with depth Pressure is greatest at bottom Upward force against the bottom are greater than the downward forces against top Buoyant force

  44. 13.3 Archimedes

  45. Archimedes’ Principle • An immersed body is buoyed up by a force equal to the weight of the fluid it displaces. • True to all fluids, liquids and gases • Ex. 7lb object displaced 3lb of water, the buoyant force is 3lbs and the apparent weight is 4lbs.

  46. Archimedes’ Principle

  47. Weight is greater than the buoyant force the object sinks Weight is still greater than the buoyant force Buoyant force is = to the weight and the object floats Buoyant force

  48. Weight and the Buoyant Force

  49. Buoyant force A sunken object displaces its own volume of liquid.A floating object displaces its own mass of liquid.Buoyant force is equal to the weight of the displaced liquid, whether the object is submerged or floating.

  50. Alcohol Water Glycerin Partial Submersion Density of the fluid makes things float

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