Page 81, 1. All fluids exert _______, which is the amount of force exerted on a given area.pressurePage 81, 2. The pressure of all fluids increase as _______ increases. depthPage 81, 3. Buoyant force on an object is the upward force equal to the _______ of the fluid displacedweight

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

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

Chapter 3

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.

Section 2 FluidsChapter 3

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.

Section 2 FluidsChapter 3

https://video.search.yahoo.com/yhs/search;_ylt=AwrCwGF3Nv9bXRgAfnQPxQt.;_ylu=X3oDMTByMjB0aG5zBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzYw--?p=archimedes+principle+youtube+lego&fr=yhs-pty-pty_email&hspart=pty&hsimp=yhs-pty_email#id=3&vid=69a90452a45050cd68122c0741baffa5&action=view

https://video.search.yahoo.com/yhs/search?fr=yhs-pty-pty_email&hsimp=yhs-pty_email&hspart=pty&p=archimedes+lego+eureka+youtube+video#id=3&vid=65c40604ee30c2b1bd21c9c5e8e6c1fd&action=view

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.

Section 2 FluidsChapter 3

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.

Section 2 FluidsChapter 3

Section 2 FluidsChapter 3

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.

Section 2 FluidsChapter 3

Pressure can be calculated by dividing force by the area over which the force is exerted:

forcepressure

area=

Section 2 FluidsChapter 3

• 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).

forcepressure

area=

Section 2 FluidsChapter 3

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.

Section 2 FluidsChapter 3

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?

Section 2 FluidsChapter 3

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.

1 2

1 2

F F

A A= 2 1

1

2

( )( )F AF

A=

Section 2 FluidsChapter 3

3. Insert the known values into the equation, and solve.

2

1 2

(19,000 N)(10.5 cm )

400 cmF =

Section 2 FluidsChapter 3

F1 = 500 N

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).

Section 2 FluidsChapter 3

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.

Section 2 FluidsChapter 3

Section 2 FluidsChapter 3

http://www.aviation-for-kids.com/paper-airplanes.html

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 ____ priciplePascal’s

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