Chapter 3:
States of Matter
SECTION 3:
FLUIDS
BELLRINGER
 Take out a sheet of paper, tear it in half and share
with a neighbor.
 You will have 5 minutes to complete these 4
questions.
 If the concept is unfamiliar to you, take an educated
guess.
Bellringer
1.
2.
3.
4.
1. Is the buoyant force on the lump of gold greater than, less than, or
equal to the gold’s weight?
2. Is the buoyant force on the balloon greater than, less than, or
equal to the balloon’s weight?
3. Is the buoyant force on the boat greater than, less than, or equal to
the boat’s weight?
4. Is the buoyant force on the submarine greater than, less than, or
equal to the submarine’s weight?
Section 3: Fluids
 You’ve probably heard of air pressure, blood
pressure, and water pressure…but, what is pressure?
Pressure is the amount of
force exerted on a given
area of surface.
Which of the following states of matter can flow?
Pl
as
m
Ga
se
s
sa
nd
nd
So
lid
ds
a
0%
Bo
th
qu
i
Li
0%
as
0%
sm
as
0%
Pl
a
0%
Bo
th
0%
Ga
se
s
6.
s
5.
ui
d
4.
Liq
3.
id
s
2.
Solids
Liquids
Gases
Plasmas
Both Liquids and
Gases
Both Solids and
Plasmas
So
l
1.
30
REMEMBER
BECAUSE THE
PARTICLES OF LIQUIDS
AND GASES SLIDE PAST
ONE ANOTHER, THEY
ARE SAID TO FLOW.
Pressure
〉How do fluids exert pressure?
〉Fluids exert pressure evenly in all directions.

pressure: the amount of force exerted per unit area of
a surface

example: when you pump
up a bicycle tire, air particles
constantly push against each
other and against the tire walls
PRESSURE
 Pressure is calculated by dividing force by the area
over which the force is exerted.
force
pressure 
area
F
P
A
SI UNIT
 The SI Unit for measuring pressure is
called the PASCAL.
 One pascal (1 Pa) is the force of one
newton exerted over the area of one
square meter (1 N/m2).
 Newtons are the SI Unit used to
measure force.
Buoyant Force
 The upward force that keeps an object immersed in
or floating on a fluid.
 If you push a rubber duck to the bottom of the tub,
what happens when you let it go?
What unit do we use to measure pressure?
1. Pascal
2. Newton
3. Meter
4. Gram
0%
Gr
am
et
er
0%
M
to
n
0%
Ne
w
Pa
sc
a
l
0%
30
What unit do we use to measure length?
1. Pascal
2. Newton
3. Meter
4. Gram
0%
Gr
am
et
er
0%
M
to
n
0%
Ne
w
Pa
sc
a
l
0%
30
What SI unit do we use to measure force?
1. Pascal
2. Newton
3. Meter
4. Gram
0%
Gr
am
et
er
0%
M
to
n
0%
Ne
w
Pa
sc
a
l
0%
30
Buoyant Force
Buoyant Force, continued
•
Archimedes’ principle is used to
find buoyant force.
– The
buoyant force on an object in
a fluid is an upward force equal to
the weight of the fluid that the
object displaces.
Comparing Weight and Buoyant Force
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.
Bellringer
1.
2.
3.
4.
1. Is the buoyant force on the lump of gold greater than, less than, or
equal to the gold’s weight? LESS THAN
2. Is the buoyant force on the balloon greater than, less than, or
equal to the balloon’s weight? GREATER THAN
3. Is the buoyant force on the boat greater than, less than, or equal to
the boat’s weight? EQUAL TO
4. Is the buoyant force on the submarine greater than, less than, or
equal to the submarine’s weight? EQUAL TO
FOR HOMEWORK
 MEMORIZE ARCHIMEDES’
PRINCIPLE (write it 5 times).
 The buoyant force on an object in a fluid is an
upward force equal to the weight of the fluid that
the object displaces.
 Questions 1 & 2 on page 94.
BELLRINGER
 TODAY, YOU WILL ONLY HAVE 90 SECONDS TO
ANSWER THE BELLRINGER QUESTION.
BELLRINGER #1
 State Archimedes’ Principle.
BELLRINGER #2
 1. How does the ship’s density compare with the
density of the water?
Pascal’s Principle
 When you squeeze on one of an unopened tube of
toothpaste, what happens?
 The reason the toothpaste comes out the other side is
because we applied pressure to one end of the tube
and that pressure is transmitted throughout the
tube.
Pascal’s Principle
〉What happens when pressure in a fluid changes?
〉Pascal’s principle states that a change in pressure at
any point in an enclosed fluid will be transmitted
equally to all parts of the fluid. In other words, if the
pressure in a container is increased at any point, the
pressure increases at all points by the same amount.

Mathematically, Pascal’s principle is stated as
P1 = P2.

Because P = F/A, Pascal’s principle can also be expressed
as F1/A1 = F2/A2.
Pascal’s Principle, continued
 Hydraulic devices are based on Pascal’s principle.

Because the pressure is the same on both sides of the enclosed
fluid, a small force on the smaller area (left) produces a much
larger force on the larger area (right).
– The plunger
travels through
a larger
distance on the
side that has
the smaller
area.
Math Skills
Pascal’s Principle
A hydraulic lift uses 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?
1. List the given and unknown values.
Given: F2 = 19,000 N
A1 = 10.5 cm2
A2 = 400 cm2
Unknown:
F1
Math Skills, continued
2. Start with Pascal’s principle, and
substitute the equation for pressure. Then,
rearrange the equation to isolate the
unknown value.
P1 = P2
F1 F 2

A1 A2
( F 2)( A1)
F1 
A2
Math Skills, continued
3. Insert the known values into the equation,
and solve.
(19,000 N)(10.5 cm2 )
F1 
400 cm2
F1 = 500 N
Fluids in Motion
〉What affects the speed of a fluid in motion?
〉Fluids move faster through small areas than
through larger areas, if the overall flow rate
remains constant. Fluids also vary in the rate at
which they flow.
Fluids in Motion, continued
 Viscosity depends on particle attraction.

viscosity: the resistance of a gas or liquid to flow
 Fluid pressure decreases as speed increases.

This is known as Bernoulli’s principle.
Viscosity
HOMEWORK
For homework, complete the
Concept Review for Section 3.
There will be a reading quiz
tomorrow.