1. Warm-up
Page 83, 1. All fluids exert a __________. pressure Page 83, 2. The equation for pressure is: Pressure = force/area Page 83, 3. The SI unit for pressure is the _______. Pascal which is 1N/m²

2. Today’s Objectives: Students will be able to…
Describe buoyant force – why things float
Define Archimandrites principles – how it relates to human activities -
Explain the role of density
State and apply pascal’s principle – drawing – where it is used/how

3. Activities: Warm-up / quiz Notes/discussion Video clips / discussion
Phet lab solid liquid gas – review sec. 1
Concept review section 1 chap. 3

4. Objectives
Chapter 3
Section 2 Fluids
Describe the buoyant force and explain how it keeps objects afloat.
Define Archimedes’ principle.
Explain the role of density in an object’s ability to float.
State and apply Pascal’s principle.

5. Chapter 3
Section 2 Fluids
Fluids
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 liquid.
Fluids are able to flow because their particles can move past each other easily.
The properties of fluids allow huge ships to float, divers to explore the ocean depths, and jumbo jets to soar across the skies.

6. fluids

8. Chapter 3
Section 2 Fluids
Buoyant Force
Buoyant force is the upward force exerted on an object immersed in or floating on a fluid.
Buoyancy explains why objects float.
All fluids exert pressure: the amount of force exerted per unit area of a surface.
Archimedes’ principle states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of fluid that the object displaces.

9. Archimedes' principle

10. Buoyant Force, continued
Chapter 3
Section 2 Fluids
Buoyant Force, continued
The volume of fluid displaced by an object placed in a fluid will be equal to the volume of the part of the object submerged.
The figure below shows how displacement works.

11. Buoyant Force, continued
Chapter 3
Section 2 Fluids
Buoyant Force, continued
An object will float or sink based on its density.
If an object is less dense than the fluid in which it is placed, it will float.
If an object is more dense than the fluid in which it is placed, it will sink.

12. Chapter 3
Section 2 Fluids
Density

13. Fluids and Pressure Fluids exert pressure evenly in all directions.
Chapter 3
Section 2 Fluids
Fluids and Pressure
Fluids exert pressure evenly in all directions.
For example, when you pump up a bicycle tire, air particles are constantly pushing against each other and against the walls of the tire.

14. Fluids and Pressure, continued
Chapter 3
Section 2 Fluids
Fluids and Pressure, continued
Pressure can be calculated by dividing force by the area over which the force is exerted:
The SI unit for pressure is the pascal (abbreviation: Pa), equal to the force of one newton exerted over an area of one square meter (1 N/m2).

15. What is a Newton ?
the absolute unit of force in the International System of Units (SI units). It is defined as that force necessary to provide a mass of one kilogram with an acceleration of one meter per second per second. It is equivalent to kg m/s² - Like holding 100 grams in your hand

16. Chapter 3
Section 2 Fluids
Equation for Pressure

17. Chapter 3
Section 2 Fluids
Pascal’s Principle
Pascal’s principle states that a fluid in equilibrium contained in a vessel exerts a pressure of equal intensity in all directions.
Mathematically, Pascal’s principle is stated as p1 = p2, or pressure1 = pressure2.

18. Chapter 3
Section 2 Fluids
Math Skills
Pascal’s Principle A hydraulic lift, shown in the figure below, makes use of Pascal’s principle, to lift a 19,000 N car. If the area of the small piston (A1) equals 10.5 cm2 and the area of the large piston (A2) equals 400 cm2, what force needs to be exerted on the small piston to lift the car?

19. Chapter 3
Section 2 Fluids
Math Skills, continued
1. List the given and unknown values. Given: F2 = 19,000 N A1 = 10.5 cm2 A2 = 400 cm2 Unknown: F1
2. Write the equation for Pascal’s principle. According to Pascal’s principle, p1 = p2.

20. Chapter 3
Section 2 Fluids
Math Skills, continued
3. Insert the known values into the equation, and solve.
F1 = 500 N

21. Pascal’s Principle, continued
Chapter 3
Section 2 Fluids
Pascal’s Principle, continued
Hydraulic devices are based on Pascal’s principle.
Hydraulic devices can multiply forces, as shown in the figure below. Because the pressure is the same on both sides of the enclosed fluid, a small force on the smaller area (at left) produces a much larger force on the larger area (at right).

22. Chapter 3
Section 2 Fluids
Fluids in Motion
Viscosity is the resistance of a gas or liquid to flow.
Bernoulli’s principle states that as the speed of a moving fluid increases, the pressure of the moving fluid decreases.
Bernoulli’s principle is illustrated below: as a leaf passes through a drainage pipe from point 1 to point 2, it speeds up, and the water pressure decreases.

24. Chapter 3
Section 2 Fluids
Viscosity

25. Video clips

26. Cool down
1. Going from solid to liquid to gas what is the main change in the molecules of a substance? The amount of energy the particles have in increased – temperature overall increased 2. What happens to the spacing between particles as you cool a substance down? Particles gather closer together overall motion decreases

27. Cool down
1. Does a block of wood have a higher buoyancy force in water or oil ? water 2. If buoyant force is equal to the ______ of the volume of the fluid displaced. weight

28. Cool down
1. Why do you weigh less in water? (what is this principle called?) It has a buoyant force pushing upwards – Archimedes principle 2. Hydraulic devices are based on ____ priciple Pascal’s

29. Cool down
1. On an air plane wing where is pressure the lowest? Above the wing 2. Hydraulic devices are based on ____ principle Pascal’s