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The Fluid States Section 13.1 Physics. Objectives  Describe how fluids create pressure and relate Pascal’s principle to some everyday occurrences. 

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Presentation on theme: "The Fluid States Section 13.1 Physics. Objectives  Describe how fluids create pressure and relate Pascal’s principle to some everyday occurrences. "— Presentation transcript:

1 The Fluid States Section 13.1 Physics

2 Objectives  Describe how fluids create pressure and relate Pascal’s principle to some everyday occurrences.  Apply Archimedes’ and Bernoulli’s principles.  Explain how forces within liquids cause surface tension and capillary action, and relate the kinetic model to evaporation and condensation.

3 Properties of Fluids  Fluids: materials that flow and have no definite shape of their own.  For the most part, Newton’s Laws and the Laws of Conservation can be applied to fluids.  When we apply a force to a fluid, what do we call it?

4 Pressure  We call a force applied to a fluid: pressure.  Pressure is represented by the following equation: P = F/A P = F/A Pressure equals force divided by area. Pressure equals force divided by area.

5 Pressure  The force is assumed to be perpendicular to the affected surface area.  Pressure is measured in Pascals, Pa.  The Pascal: 1N/m².  Which has a greater pressure? The area under an elephant’s foot or the area under a woman’s high heel shoe? The area under an elephant’s foot or the area under a woman’s high heel shoe? The area under a high heel shoe. The area under a high heel shoe.

6 Pressure from a Gas?  It is easy to see how solids and fluids exert pressure on a surface.  But how does a gas exert pressure on an area?  The tiny gas particles are constantly hitting surfaces and applying a pressure value.

7 Pressure from a Gas  Are we under pressure right now?  Yep.  In fact, on every square centimeter of Earth’s surface at sea level, the atmosphere exerts a force of approximately 10 N = 1 kg.  Blue Barometer Demo.

8 Practice Problems  Pg 303  1-4

9 Fluids at Rest  Water also exerts pressure just as the atmosphere exerts pressure.  Think of a diver, the pressure felt when under water does not depend on whether the diver is upright, sideways, or up-side- down.  Pascal’s Principle accounts for this pressure.

10 Pascal’s Principle  Pascal’s Principle: any change in pressure applied at any point on a confined fluid is transmitted undiminished throughout the fluid.  How does toothpaste demonstrate this principle?

11 Pascal’s Principle  So why is this important?  There are more important reasons than that of toothpaste.  Hydraulic systems use this principle  Force Exerted by lift = F = (F 1 A 2 )/A 1

12 Practice Problem  Pg 304  5

13 Swimming Under Pressure  When you dive under water, your body feels increasing pressure as you dive deeper.  The downward pressure of water is illustrated by the following equation.  P = ρhg  Rho; density of fluid, h; depth, g; gravity.

14 Swimming Under Pressure  While swimming, you may also notice the upward force from the water you are immersed in.  This force is the buoyant force.  F buoyant = ρVg  Rho; density, V; volume, g; gravity.  The net upward force is equal to the weight of the fluid displaced by the object.

15 Archimedes’ Principle  The buoyant force and weight of displaced fluid relationship was discovered by the Greek scientist Archimedes.  Archimedes’ Principle: states that an object immersed in a fluid has an upward force on it equal to the weight of the fluid displaced by the object; it does not depend on the weight of the object.

16 So Will It Sink Or Float?  When an object is placed in a fluid, it has the force of gravity pressing down and the buoyant force pressing up.  The difference between the two determines if the object will sink or float.  F apparent = F g – F buoyant  A negative value for F apparent indicates the object will float.

17 Practice Problems  Pg 309  6-7

18 Fluids in Motion  Ok, we have looked at static fluids, but fluids do not just stay still.  Bernoulli’s Principle: describes the relationship between the velocity and pressure exerted by a moving fluid.  Bernoulli’s Principle states that as the velocity of a fluid increases, the pressure exerted by that fluid decreases.

19 Fluids in Motion  Most airplanes get part of their lift by utilizing this principle.  The curvature of the top wing is greater than that of the bottom.  As the wing travels through the air, ;the air moving over the top surface travels faster than air moving past the bottom surface.

20 Fluids in Motion  The decreased air pressure created on the top surface results in a net upward pressure that produces an upward force on the wings, or lift, which helps hold the plane up.  Race cars use this same principle…How?

21 Forces Within Liquids  All of the fluids examined thus far have been ideal fluids.  In real liquids, particles exert electromagnetic forces of attraction on each other.  These forces affect the behavior of liquids.

22 Forces Within Liquids  These forces are cohesive forces.  Cohesive forces are the forces of attraction between particles of a fluid.  These forces account for water’s surface tension.

23 Forces Within Liquids  Another force that affects the way a fluid behaves is adhesion.  Adhesive forces are the attraction between particles of a fluid and the particles of another surface.  This is why capillary action occurs.


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