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Title: Chapter 2, Section 2


1
Chapter 2, Section 2Measuring Matter
  • Weight, mass, volume density

2
Section 2 Measuring Matter
  • OBJECTIVES
  • Distinguish between the mass and weight of an
    object.

3
The International System of Units
  • OBJECTIVES
  • List SI units of measurement and common SI
    prefixes.

4
Mass vs Weight
5
Units of Mass
  • Mass is a measure of the quantity of matter
    present
  • Weight is a force that measures the pull by
    gravity- it changes with location
  • Mass is constant, regardless of location

6
Weight is the Pull of Gravity
  • Weight is a measure of the pull of gravity.
  • Weight is measured with a spring that is
    compressed or stretched.

7
All Matter has Gravity
  • The elephant has more matter so it has more mass,
    so it has more gravity.
  • Even dust is matter so it pulls other dust
    together by gravity.

8
Weight vs. Mass
  • Weight changes when the pull of gravity changes
  • The Earth is six times the mass of the moon.
  • On Earth the astronaut weighs 185 lbs.
  • Moon has 1/6th the gravity so the astronaut
    weighs only 31 lbs.
  • Weight is not about the astronaut, its about the
    mass of object theyre standing on.

9
Mass is a Comparison
  • Mass is measured with balance, it works like a
    teeter totter.
  • Something is placed on one side.
  • Something else is placed on the other side till
    it balanced.
  • In the metric system everything is compared to
    water.
  • 1ml H2O 1g H2O
  • or 1liter H2O 1kg H2O

10
Mass Does Not Change
  • While on the Earth I will place an object on one
    side of a balance and an equal amount of water on
    the other side.
  • Now I will travel to the moon.
  • Once on the moon I will repeat the experiment.
  • Although the moon pulls 1/6th as hard on the
    object, it also pulls 1/6th as hard on the water,
    so it still balances.
  • For this reason scientists prefer to measure
    matter by its mass not weight.

11
Working with Mass
  • The SI unit of mass is the kilogram (kg), even
    though a more convenient everyday unit is the
    gram
  • Measuring instrument is the balance scale

12
Measuring Mass Triple-Beam Balance
5th Add the amounts on each beam to find the
total mass to the nearest tenth of a gram.
Click here to try an online activity.
13
Measuring Mass
We will be using triple-beam balances to find the
mass of various objects. The objects are placed
on the scale and then you move the weights on the
beams until you get the lines on the right-side
of the scale to match up.
Top Image http//www.southwestscales.com/Ohaus_Tr
iple_Beam_750-SO.jpgBottom Image
http//www.regentsprep.org/Regents/biology/units/l
aboratory/graphics/triplebeambalance.jpg
14
Measuring
  • The numbers are only half of a measurement
  • Measurement number unit
  • It has a mass of 10
  • 10 what??
  • Numbers without units are meaningless.
  • You will lose credit is you do not include your
    units!

15
The International System of Units
  • OBJECTIVES
  • List SI units of measurement and common SI
    prefixes.

16
Section 2 Measuring Matter
  • OBJECTIVES
  • Identify the units of volume density
  • Explain how density is determined

17
International System of Units
  • Measurements depend upon units that serve as
    reference standards
  • The standards of measurement used in science are
    those of the Metric System

18
The Metric System
  • Easier to use because it is a decimal system
  • Every conversion is by some power of 10.
  • A metric unit has two parts
  • A prefix and a base unit.
  • prefix tells you how many times to divide or
    multiply by 10.

19
Length
  • In SI, the basic unit of length is the meter (m)
  • Length is the distance between two objects
    measured with ruler
  • We make use of prefixes for units larger or
    smaller

20
SI Prefixes Page 74Common to Science
Prefix Unit Abbreviation Meaning Exponent
Kilo- k thousand 103
Deci- d tenth 10-1
Centi- c hundredth 10-2
Milli- m thousandth 10-3
Micro- ? millionth 10-6
Nano- n billionth 10-9
21
Volume
  • The space occupied by any sample of matter.
  • Calculated for a solid by multiplying the length
    x width x height thus derived from units of
    length.
  • SI unit cubic meter (m3)
  • Everyday unit Liter (L), which is non-SI.
    (Note 1mL 1cm3)

22
Recap Review
  • Volume is
  • The space occupied by any sample of matter.
  • Mass is
  • The amount of matter in an object
  • Weight is
  • The force (or pull) of gravity on an object based
    on its mass
  • Which changes when your on the moon, your mass or
    weight?
  • Your weight
  • What is the SI unit for Mass, Volume and Length
  • Mass kg (kilogram)
  • Volume m3 (cubic meter), we will use liters and
    milliliters in this class
  • Length m (meter)
  • What is bigger a millimeter or a kilometer? By
    how much?
  • A kilometer (1000 meters) is bigger
  • A millimeter is 1/1000 of a meter so a kilometer
    is 1 million times bigger

23
Section 2 Measuring Volume Density
  • OBJECTIVES
  • Define what density is
  • Identify the units of volume density
  • Explain how density is determined

24
Measuring Volume Density
  • Volume is
  • The space occupied by any sample of matter.
  • Mass is
  • The amount of matter in an object
  • Density is ?????

25
Measuring Volume Density
  • Density
  • -A measure of how much matter is packed into a
    given volume
  • Which square is more dense?

26
Which one is more dense?
  • Now which one is more dense?

27
Density
? how tightly packed the particles are
Density
Typical units
g/cm3 for solids
g/mL for fluids
28
Density
  • Which is heavier- a pound of lead or a pound of
    feathers?
  • Most people will answer lead, but the weight is
    exactly the same
  • They are normally thinking about equal volumes of
    the two
  • The relationship here between mass and volume is
    called Density

29
Density
  • The formula for density is
  • mass
  • volume
  • Common units are g/mL, or possibly g/cm3, (or
    g/L for gas)
  • Density is a physical property, and does not
    depend upon sample size

Density
30
Measuring Volume
We will be using graduated cylinders to find the
volume of liquids and other objects.
Read the measurement based on the bottom of the
meniscus or curve. When using a real cylinder,
make sure you are eye-level with the level of the
water. What is the volume of water in the
cylinder? _____mL
Top Image http//www.tea.state.tx.us/student.asse
ssment/resources/online/2006/grade8/science/images
/20graphicaa.gifBottom Image http//morrisonlabs
.com/meniscus.htm
31
Measuring Solid Volume
We can measure the volume of regular object using
the formula length x width x height.
_____ X _____ X _____ _____
Click here for an online activity about volume.
Choose Lessons ? Volume Displacement
32
Density
M V
D
M
M D x V
ass
D
V
M D
V
ensity
olume
33
To find volume, use
1.
a formula
V p r2 h
V l w h
2.
water displacement
Vfinal
Vinit
Vobject Vfinal Vinit
34
Density of water
1.0 g/mL 1.0 g/cm3
Things that are less dense float in things that
are more dense.
(And things that are more dense sink in things
that are less dense.)
D lt 1 g/cm3
D lt 1 g/cm3
D gt 1 g/cm3
D lt 1 g/cm3
The density of a liquid or solid is nearly
constant, no matter what the samples temperature.
Density of gases is highly dependent on
temperature.
35
So why is an aircraft carrier less dense than
water?
  • Its mass of steel is spread across a huge volume
    with lots of empty space in between
  • Since Density Mass/Volume
  • The mass of the steel spread across the huge
    volume gives a density lt 1.0 g/cm3 (less than
    water)

Things that are less dense float in things
that are more dense.
D lt 1 g/cm3
36
Density of Some Common Substances (Density is a
physical property of matter)
Substance
Density
(g / cm3) Air
0.0013 Lithium 0.53 Ice
0.917 Water 1.00 Aluminum
2.70 Iron 7.86
Lead 11.4 Gold 19.3
at 0oC and 1 atm pressure
37
Two ways of viewing density
Dorin, Demmin, Gabel, Chemistry The Study of
Matter , 3rd Edition, 1990, page 71
38
Density and Temperature
  • What happens to the density as the temperature of
    an object increases?
  • Mass remains the same
  • Most substances increase in volume as temperature
    increases
  • Thus, density generally decreases as the
    temperature increases

39
Density and Water
  • Water is an important exception to the previous
    statement.
  • Over certain temperatures, the volume of water
    increases as the temperature decreases (Do you
    want your water pipes to freeze in the winter?)
  • Does ice float in liquid water?
  • Why?

40
Note temperature and density units
- Page 90
41
Measure Density for yourself
  • Complete Skills Lab Making Sense of Density
  • Complete skills lab data table questions (Due
    tomorrow)
  • Complete Measuring Matter and Density Work Sheet
    (Due Friday)

42
Density Review
43
  • Density Calculations

1. A sample of lead (Pb) has mass 22.7 g and
volume 2.0 cm3. Find samples density.
11.35
2. Another sample of lead occupies 16.2 cm3
of space. Find samples mass.
m D V
184
g
44
3. A 119.5 g solid cylinder has radius 1.8 cm
and height 1.5 cm. Find samples density.
V p r2 h
p (1.8 cm)2(1.5 cm)
15.3
cm3
7.81
45
4. A 153 g rectangular solid has edge lengths
8.2 cm, 5.1 cm, and 4.7 cm. Will this
object sink in water?
(Find objects density and compare it to waters
density.)
V l w h
8.2 cm (5.1 cm)(4.7 cm)
197
cm3
No it floats.
0.78
lt 1
46
- Page 91
47
- Page 92
48
End of Section 2 Measuring Matter
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