Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Mass Density Section 1 Fluids and Buoyant Force

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Buoyant Force and Archimedes’ Principle Section 1 Fluids and Buoyant Force

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Displaced Volume of a Fluid Section 1 Fluids and Buoyant Force

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Fluids and Buoyant Force 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

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Buoyant Force on Floating Objects Section 1 Fluids and Buoyant Force

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Buoyant Force Section 1 Fluids and Buoyant Force

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Fluids and Buoyant Force 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:

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 = ?

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 2. Plan, continued Rearrange the equation to isolate the unknown:

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Fluids and Buoyant Force Chapter 8 Sample Problem, continued Buoyant Force 3. Calculate Substitute the values into the equation and solve:

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Pascal’s Principle Section 2 Fluid Pressure

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Fluid Pressure Chapter 8 Pressure, continued Pressure varies with depth in a fluid. The pressure in a fluid increases with depth.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Fluid Pressure as a Function of Depth Section 2 Fluid Pressure

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Characteristics of an Ideal Fluid Section 3 Fluids in Motion

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 8 Bernoulli’s Principle Section 3 Fluids in Motion