chapter 16

Lesson 2Lesson 2

Chapter 16Chapter 16

Properties of FluidsProperties of Fluids

A fluid is a gas or a liquidA fluid is a gas or a liquid– despite their weight ships are able to despite their weight ships are able to

float. float. – greater force pushing up on the ship greater force pushing up on the ship

opposes the weight—or force—of the opposes the weight—or force—of the ship pushing down.ship pushing down.

Archimedes’ PrincipleArchimedes’ Principle Buoyant ForceBuoyant Force

– upward force exerted by a fluid on an upward force exerted by a fluid on an immersed objectimmersed object

– buoyant force > weightbuoyant force > weight

– buoyant force = weight buoyant force = weight

– buoyant force < weightbuoyant force < weight

balloon rises

balloon sinks

balloon floats

More water needs to be displaced in order to cancel weight ball floats lower in the water.

Not enough water is displaced in order to cancel weight ball sinks.

Archimedes’ PrincipleArchimedes’ Principle

Archimedes’ PrincipleArchimedes’ Principle– the buoyant force on an object in a fluid is the buoyant force on an object in a fluid is

equal to the weight of fluid displaced by the equal to the weight of fluid displaced by the objectobject

Very little water needs to be displaced in order to cancel weight ball floats on surface.

View animations produced by students at Poly Prep Country Day School in Brooklyn, New York .

View Buoyancy JAVA Applet.

DensityDensity

object will float if its density is less object will float if its density is less than the fluid it is in.than the fluid it is in.

Suppose you form a steel block into Suppose you form a steel block into the shape of a hull filled with air. the shape of a hull filled with air. Now the same mass takes up a Now the same mass takes up a larger volume. The overall density of larger volume. The overall density of the steel boat and air is less than the the steel boat and air is less than the density of water. The boat will now density of water. The boat will now float.float.

Pascal’s PrinciplePascal’s Principle

PressurePressure is force exerted per unit is force exerted per unit areaarea– Blaise Pascal (1692-1662), Blaise Pascal (1692-1662),

a French scientist, discovered a useful a French scientist, discovered a useful property of fluids.property of fluids.

– Pascal’s principlePascal’s principle pressure applied to a fluid is transmitted pressure applied to a fluid is transmitted

throughout the fluid. throughout the fluid. Ex: toothpaste, hydraulic lifts Ex: toothpaste, hydraulic lifts

Pascal’s PrinciplePascal’s Principle

Pascal’s PrinciplePascal’s Principle– pressure applied to a fluid is transmitted pressure applied to a fluid is transmitted

unchanged throughout the fluidunchanged throughout the fluid

A

FP

View hydraulics explanation.

2

2

1

1

A

F

A

F

Applying the PrincipleApplying the Principle

pipe filled with fluid pipe filled with fluid connects small and connects small and large cylinders. large cylinders.

pressure applied to pressure applied to the small cylinder is the small cylinder is transferred through transferred through the fluid to the large the fluid to the large cylindercylinder

Applying the PrincipleApplying the Principle

pressure remains pressure remains constant throughout constant throughout the fluid the fluid – more force is available more force is available

to lift a heavy load by to lift a heavy load by increasing the surface increasing the surface area. area.

Pascal’s PrinciplePascal’s Principle A car weighing 1000 N sits on a 250 mA car weighing 1000 N sits on a 250 m22

platform. What force is needed on the 10 mplatform. What force is needed on the 10 m22 plunger to keep the car from sinking?plunger to keep the car from sinking?

GIVEN:

Platform:F = 1000 NA = 250 m2

Plunger:F = ?A = 10 m2

(1000 N)(10 m2)=(250

m2)F2

2

2

1

1

A

F

A

FWORK:

1000 N = F2

250 m2 10 m2

F2 = 40 N

Pascal’s PrinciplePascal’s Principle A disgruntled cow that weighs 1000 N sits A disgruntled cow that weighs 1000 N sits

on a 5 m² piston. What force would need to on a 5 m² piston. What force would need to be applied to a 2 m² piston? be applied to a 2 m² piston?

GIVEN:

Platform:F = 1000 NA = 5 m2

Plunger:F = ?A = 2 m2

(1000 N)(2 m2)=(5 m2)F2

2

2

1

1

A

F

A

FWORK:

1000 N = F2

5 m2 2 m2

F2 = 400 N

Bernoulli’s PrincipleBernoulli’s Principle


– as the velocity of a fluid increases, the as the velocity of a fluid increases, the pressure exerted by the fluid decreasespressure exerted by the fluid decreases

– EXEX:airplane lift, curve balls:airplane lift, curve balls

Bernoulli – why planes fly

Bernoulli’s PrincipleBernoulli’s Principle demonstrate Bernoulli’s demonstrate Bernoulli’s

principle principle – blow across the top surface of a blow across the top surface of a

sheet of paper. sheet of paper. – The paper will rise. The paper will rise.

velocity of the air over the velocity of the air over the top is greater than that of the top is greater than that of the quiet air below it. quiet air below it. – Net force below raises the paperNet force below raises the paper


Airplane lift

View airplane wings explanation.

The downward force decrease andthe lifting force increases. Bernoulli’sprinciple states that as the velocityof a fluid increases the pressure exertedby the fluid decreases.


View atomizer explanation.

Venturi Effect - Atomizers


Venturi EffectVenturi Effect

– fluids flow faster through narrow fluids flow faster through narrow spaces causing reduced pressurespaces causing reduced pressure

– EXEX: garden sprayer, atomizer: garden sprayer, atomizer

Bernoulli’s PrincipleBernoulli’s Principle This allows the water in the hose to flow at This allows the water in the hose to flow at

a high rate of speed, creating a low a high rate of speed, creating a low pressure area above the strawlike tube. pressure area above the strawlike tube.

The concentrated chemical solution is The concentrated chemical solution is sucked up through the straw and into the sucked up through the straw and into the stream of water. stream of water.

The concentrated solution is mixed with The concentrated solution is mixed with water, reducing the concentration to the water, reducing the concentration to the appropriate level and creating a spray that appropriate level and creating a spray that is easy to apply.is easy to apply.

Fluid FlowFluid Flow Another property exhibited by fluid is its Another property exhibited by fluid is its

tendency to flow. The resistance to flow tendency to flow. The resistance to flow by a fluid is called by a fluid is called viscosityviscosity. .

When a container of liquid is tilted to allow When a container of liquid is tilted to allow flow to begin, the flowing particles will flow to begin, the flowing particles will transfer energy to the particles that are transfer energy to the particles that are stationary. stationary.

Temperature and viscosity are inversely Temperature and viscosity are inversely related; that is higher temperature related; that is higher temperature means lower viscositymeans lower viscosity

Fluid FlowFluid Flow In effect, the flowing particles are pulling the In effect, the flowing particles are pulling the

other particles, causing them to flow, too.other particles, causing them to flow, too. If the flowing particles do not effectively pull If the flowing particles do not effectively pull

the other particles into motion, then the the other particles into motion, then the liquid has a high viscosity, or a high liquid has a high viscosity, or a high resistance to flow. resistance to flow.

If the flowing particles pull the other If the flowing particles pull the other particles into motion easily, then the liquid particles into motion easily, then the liquid has low viscosity, or a low resistance to flow. has low viscosity, or a low resistance to flow.

Temperature and viscosity are Temperature and viscosity are inversely related; that is inversely related; that is higher temperature means lower higher temperature means lower viscosityviscosity

chapter 16

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