1. Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force

2. Chapter 8 Objectives Define a fluid. Distinguish a gas from a liquid. Determine the magnitude of the buoyant force exerted on a floating object or a submerged object. Explain why some objects float and some objects sink.

3. Section 1 Fluids and Buoyant Force Chapter 8 Defining a Fluid A fluid is a nonsolid state of matter in which the atoms or molecules are free to move past each other, as in a gas or a liquid. Both liquids and gases are considered fluids because they can flow and change shape. Liquids have a definite volume; gases do not.

4. Section 1 Fluids and Buoyant Force Chapter 8 Density and Buoyant Force The concentration of matter of an object is called the mass density. Mass density is measured as the mass per unit volume of a substance.

5. Click below to watch the Visual Concept. Visual Concept Chapter 8 Section 1 Fluids and Buoyant Force Mass Density

6. Section 1 Fluids and Buoyant Force Chapter 8 Density and Buoyant Force, continued The buoyant force is the upward force exerted by a liquid on an object immersed in or floating on the liquid. Buoyant forces can keep objects afloat.

7. Click below to watch the Visual Concept. Chapter 8 Section 1 Fluids and Buoyant Force Buoyant Force and Archimedes’ Principle Visual Concept

8. Chapter 8 Displaced Volume of a Fluid Section 1 Fluids and Buoyant Force

9. Chapter 8 Density and Buoyant Force, continued Archimedes’ principle describes the magnitude of a buoyant force. Archimedes’ principle: Any object completely or partially submerged in a fluid experiences an upward buoyant force equal in magnitude to the weight of the fluid displaced by the object. F B = F g (displaced fluid) = m f g magnitude of buoyant force = weight of fluid displaced

10. Click below to watch the Visual Concept. Visual Concept Chapter 8 Section 1 Fluids and Buoyant Force Buoyant Force on Floating Objects

11. Chapter 8 Buoyant Force Section 1 Fluids and Buoyant Force

12. Chapter 8 Density and Buoyant Force, continued For a floating object, the buoyant force equals the object’s weight. The apparent weight of a submerged object depends on the density of the object. For an object with density  O submerged in a fluid of density  f, the buoyant force F B obeys the following ratio:

13. Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem Buoyant Force A bargain hunter purchases a “gold” crown at a flea market. After she gets home, she hangs the crown from a scale and finds its weight to be 7.84 N. She then weighs the crown while it is immersed in water, and the scale reads 6.86 N. Is the crown made of pure gold? Explain.

14. Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 1. Define Given: F g = 7.84 N apparent weight = 6.86 N  f = p water = 1.00  10 3 kg/m 3 Unknown:  O = ?

15. Section 1 Fluids and Buoyant Force Chapter 8 Diagram: Sample Problem, continued Buoyant Force 1. Define, continued TIP: The use of a diagram can help clarify a problem and the variables involved. In this diagram, F T,1 equals the actual weight of the crown, and F T,2 is the apparent weight of the crown when immersed in water.

16. Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 2. Plan Choose an equation or situation: Because the object is completely submerged, consider the ratio of the weight to the buoyant force.

17. Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 2. Plan, continued Rearrange the equation to isolate the unknown:

18. Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 3. Calculate Substitute the values into the equation and solve:

19. Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 4. Evaluate From the table, the density of gold is 19.3  10 3 kg/m 3. Because 8.0  10 3 kg/m 3 < 19.3  10 3 kg/m 3, the crown cannot be pure gold.

20. Preview Objectives Pressure Chapter 8 Section 2 Fluid Pressure

21. Chapter 8 Objectives Calculate the pressure exerted by a fluid. Calculate how pressure varies with depth in a fluid.

22. Section 2 Fluid Pressure Chapter 8 Pressure Pressure is the magnitude of the force on a surface per unit area. Pascal’s principle states that pressure applied to a fluid in a closed container is transmitted equally to every point of the fluid and to the walls of the container.

23. Click below to watch the Visual Concept. Visual Concept Chapter 8 Section 2 Fluid Pressure Pascal’s Principle

24. Section 2 Fluid Pressure Chapter 8 Pressure, continued Pressure varies with depth in a fluid. The pressure in a fluid increases with depth.

25. Click below to watch the Visual Concept. Visual Concept Chapter 8 Section 2 Fluid Pressure Fluid Pressure as a Function of Depth

26. Preview Objectives Fluid Flow Principles of Fluid Flow Chapter 8 Section 3 Fluids in Motion

27. Chapter 8 Objectives Examine the motion of a fluid using the continuity equation. Recognize the effects of Bernoulli’s principle on fluid motion.

28. Section 3 Fluids in Motion Chapter 8 Fluid Flow Moving fluids can exhibit laminar (smooth) flow or turbulent (irregular) flow. An ideal fluid is a fluid that has no internal friction or viscosity and is incompressible. The ideal fluid model simplifies fluid-flow analysis.

29. Click below to watch the Visual Concept. Visual Concept Chapter 8 Section 3 Fluids in Motion Characteristics of an Ideal Fluid

30. Section 3 Fluids in Motion Chapter 8 Principles of Fluid Flow The continuity equation results from conserva- tion of mass. Continuity equation A 1 v 1 = A 2 v 2 Area  speed in region 1 = area  speed in region 2

31. Section 3 Fluids in Motion Chapter 8 Principles of Fluid Flow, continued The speed of fluid flow depends on cross- sectional area. Bernoulli’s principle states that the pressure in a fluid decreases as the fluid’s velocity increases.

32. Click below to watch the Visual Concept. Visual Concept Chapter 8 Section 3 Fluids in Motion Bernoulli’s Principle