Chapter 16
Lesson 2
Properties of Fluids

A fluid is a gas or a liquid
– despite their weight ships are able to float.
– greater force pushing up on the ship
opposes the weight—or force—of the ship
pushing down.
Archimedes’ Principle

Buoyant Force
– upward force exerted by a fluid on an immersed
object
– buoyant force > weight
balloon rises
– buoyant force < weight
balloon sinks
– buoyant force = weight
balloon floats
Archimedes’ Principle

Archimedes’ Principle
– the buoyant force on an object in a fluid is
equal to the weight of fluid displaced by the
object
Very
little
water
needs
todisplaced
be displaced
in to
More
water
needs
be
in order
Not
enough
water
isto
displaced
in order
to
order
cancel
weight
 balllower
floats
cancelto
weight
ballsinks.
floats
in on
the water.
cancel
weight

ball
View Buoyancy JAVA Applet.
surface.
View animations produced by students at Poly Prep Country Day School in Brooklyn, New York.
Density
object will float if its density is less
than the fluid it is in.
 Suppose you form a steel block into the
shape of a hull filled with air. Now the
same mass takes up a larger volume.
The overall density of the steel boat
and air is less than the density of water.
The boat will now float.

Pascal’s Principle

Pressure is force exerted per unit area
– Blaise Pascal (1692-1662),
 a French scientist, discovered a useful property
of fluids.
– Pascal’s principle
 pressure applied to a fluid is transmitted
throughout the fluid.
 Ex: toothpaste, hydraulic lifts
Pascal’s Principle

Pascal’s Principle
– pressure applied to a fluid is transmitted
unchanged throughout the fluid
View hydraulics explanation.
F1
P
A1
F2
A
A2
Applying the Principle
pipe filled with fluid
connects small and large
cylinders.
 pressure applied to the
small cylinder is
transferred through
the fluid to the large
cylinder

Applying the Principle

pressure remains
constant throughout
the fluid
– more force is available
to lift a heavy load by
increasing the surface
area.
Pascal’s Principle

A car weighing 1000 N sits on a 250 m2
platform. What force is needed on the 10 m2
plunger to keep the car from sinking?
GIVEN:
Platform:
F = 1000 N
A = 250 m2
Plunger:
F=?
A = 10 m2
WORK:
1000 N =
F2
250 m2
10 m2
F1 F2

A1 A2
(1000 N)(10 m2)=(250 m2)F2
F2 = 40 N
Pascal’s Principle

A disgruntled cow that weighs 1000 N sits on
a 5 m² piston. What force would need to be
applied to a 2 m² piston?
GIVEN:
Platform:
F = 1000 N
A = 5 m2
Plunger:
F=?
A = 2 m2
WORK:
1000 N =
F2
5 m2
2 m2
F1 F2

A1 A2
(1000 N)(2 m2)=(5 m2)F2
F2 = 400 N
Bernoulli’s Principle

Bernoulli’s Principle
– as the velocity of a fluid increases, the
pressure exerted by the fluid decreases
– EX:airplane lift, curve balls
Bernoulli – why planes fly
Bernoulli’s Principle

demonstrate Bernoulli’s
principle
– blow across the top surface of a
sheet of paper.
– The paper will rise.

velocity of the air over the
top is greater than that of the
quiet air below it.
– Net force below raises the
paper
Bernoulli’s Principle
Airplane lift
View airplane wings explanation.
The downward force
decrease and
the lifting force
increases. Bernoulli’s
principle states that as
the velocity
of a fluid increases the
pressure exerted
by the fluid decreases.
Bernoulli’s Principle
Venturi Effect - Atomizers
View atomizer explanation.
Bernoulli’s Principle

Venturi Effect
– fluids flow faster through narrow spaces
causing reduced pressure
– EX: garden sprayer, atomizer
Bernoulli’s Principle
This allows the water in the hose to
flow at a high rate of speed, creating a
low pressure area above the strawlike
tube.
 The concentrated chemical solution is
sucked up through the straw and into
the stream of water.
 The concentrated solution is mixed with
water, reducing the concentration to
the appropriate level and creating a
spray that is easy to apply.

Fluid Flow
Another property exhibited by fluid is
its tendency to flow. The resistance to
flow by a fluid is called viscosity.
 When a container of liquid is tilted to
allow flow to begin, the flowing particles
will transfer energy to the particles that
are stationary.
 Temperature and viscosity are inversely
related; that is higher temperature
means lower viscosity

Fluid Flow
In effect, the flowing particles are
pulling the other particles, causing them
to flow, too.
 If the flowing particles do not
effectively pull the other particles into
motion, then the liquid has a high
viscosity, or a high resistance to flow.
 If the flowing particles pull the other
particles into motion easily, then the
liquid has low viscosity, or a low
resistance to flow.


Temperature and viscosity are inversely
related; that is higher temperature
means lower viscosity