Forces in Fluids. Pressure A force distributed over a given area. Equation for Pressure: Pressure = Force / Area. Units for Pressure: Pascal (Pa)

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2 Pressure A force distributed over a given area Equation for Pressure: Pressure = Force / Area Force = Newton s Area = m 2 Units for Pressure: Pascal (Pa) Forces in Fluids

3 Forces in Fluids A woman s high heels sink into the soft ground, but the larger shoes of the much bigger man do not. Why??? Pressure = Force / Area More area = less pressure

4 Forces in Fluids Example #1 Each tile on the bottom of a swimming pool has an area of 0.50 m 2. The water above each tile exerts a force of 11,000 N on each tile. How much pressure does the water exert on each tile? P = F / A P = 11,000 N / 0.50 m 2 P = 22,000 Pa

5 Forces in Fluids Example #2 The weight of a gallon of milk is about 38 N. If you pour a gallon of milk into a container whose bottom has an area of 0.60 m 2, how much pressure will the milk exert on the bottom of the container? P = F / A P = 38 N / 0.60 m 2 P = Pa

6 What is a Fluid? A substance that attains the shape of its container. Examples: liquids and gases. Forces in Fluids Fluid pressure changes with depth in a column of water and with altitude. Fluid pressure in water does not depend on the volume or weight. It depends only on the depth.

7 Forces in Fluids Two factors that affect fluid pressure: 1. Depth 2. Type of fluid

8 Fluid Pressure In the Water

9 Fluid Pressure In the Air How does air pressure change as altitude changes? Air pressure decreases as the altitude increases. Examples: Ears popped while on a plane Driving up mountains

Forces in Fluids Blaise Pascal 1623-1662 French physicist and

10 Forces in Fluids Blaise Pascal French physicist and mathematician Performed some of the first experiments dealing with pressure

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

12 Pascal s Principle A force applied to one section of an enclosed liquid at rest will be transferred to the entire liquid with the same amount of force.

13 Pascal s Principle Examples Forces in Fluids

14 14.2 Assessment

15 Forces in Fluids What is a hydraulic system? A device that uses pressurized fluid acting on pistons of different sizes to change a force. If the second piston has a larger surface area, the force is multiplied! Pressure = Force/Area Force/Area = Pressure = Larger Force/Larger Area

16 Force is applied to the piston Force is transmitted through the fluid to the other piston

17 On the larger piston is multiplied

18 Forces in Fluids

19 Forces in Fluids Many everyday items uses Pascal s principle and moving pistons with an enclosed pressurized fluid.

20 Forces in Fluids Everyday Examples Car brakes Amusement park rides

21 Forces in Fluids Everyday Examples Car jacks Construction machines

22 Forces in Fluids Everyday Examples Car lifts Office chairs Hollywood????

23 Forces in Fluids Bernoulli s Principle As the speed of a fluid increases, the pressure within the fluid decreases. Air always moves from higher pressure to lower pressure

24 Forces in Fluids How do we use Bernoulli s principle to make planes fly?

25 Forces in Fluids How do we use Bernoulli s principle to make planes fly (Draw diagram)?

26 Forces in Fluids

27 Two natural forces being exerted on plane: Weight Downward force of gravity Drag Resistance force created by the plane s movement through the air Drag Weight

28 Two forces a pilot needs to create to overcome weight and drag Lift Upward force on a plane (Due to force on wings) Thrust Artificially created (engines). Used to overcome drag and to sustain lift Lift Thrust

29 14.2 Assessment 1. What two things must you know to calculate pressure? Force and Area

30 14.2 Assessment 2. What is the relationship between the depth of water and the pressure it exerts? Water pressure increases as depth increases

31 14.2 Assessment 3. How is the pressure distributed at a given depth in a fluid? At any given depth, pressure is constant and exerted equally in all directions.

32 14.2 Assessment 4. How does the pressure exerted by the atmosphere change as altitude increases? Pressure decreases as altitude increases

33 14.2 Assessment 5. Give me two examples of Pascal s Principle

34 14.2 Assessment 6. How are fluid speed and fluid pressure related. As the speed of a fluid increases, the pressure within the fluid decreases.

35 7. Whose Principle is this? 14.2 Assessment Bernoulli s Principle

36 14.2 Assessment Problem #8: The weight of the gasoline in a 55 gallon drum creates a force of 1,456 Newton s. The area of the bottom of the drum is 0.80 m 2. How much pressure does the gasoline exert on the bottom of the drum? 1,820 Pa

37 14.2 Assessment Problem #9: A company makes garden statues by pouring concrete into a mold. The amount used to make a statue if a deer weighs 3,600 N. If the base of the deer statue is 0.60 m long and 0.40 meters wide, how much pressure will the statue exert on a the ground? (Hint: Area is equal to length times width) 15,000 Pa

38 14.2 Assessment Problem #10: A book with a weight of 12 N rests on its back cover. If the books cover measures 0.21 m by 0.28 m, how much pressure does the book exert? Pa

Review: Fluids. container into which it has been poured. changes gases are compressible. pressure changes

Review: Fluids. container into which it has been poured. changes gases are compressible. pressure changes Forces in Fluids Review: Fluids o A fluid is a substance that is able to flow and assume the form of the container into which it has been poured o A compressible fluid is one that can change its volume