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Chapter 2, Section 2Measuring Matter

- Weight, mass, volume density

Section 2 Measuring Matter

- OBJECTIVES
- Distinguish between the mass and weight of an

object.

The International System of Units

- OBJECTIVES
- List SI units of measurement and common SI

prefixes.

Mass vs Weight

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

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.

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.

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.

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

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.

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

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.

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

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!

The International System of Units

- OBJECTIVES
- List SI units of measurement and common SI

prefixes.

Section 2 Measuring Matter

- OBJECTIVES
- Identify the units of volume density
- Explain how density is determined

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

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.

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

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

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)

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

Section 2 Measuring Volume Density

- OBJECTIVES
- Define what density is
- Identify the units of volume density
- Explain how density is determined

Measuring Volume Density

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

Measuring Volume Density

- Density
- -A measure of how much matter is packed into a

given volume - Which square is more dense?

Which one is more dense?

- Now which one is more dense?

Density

? how tightly packed the particles are

Density

Typical units

g/cm3 for solids

g/mL for fluids

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

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

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

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

Density

M V

D

M

M D x V

ass

D

V

M D

V

ensity

olume

To find volume, use

1.

a formula

V p r2 h

V l w h

2.

water displacement

Vfinal

Vinit

Vobject Vfinal Vinit

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.

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

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

Two ways of viewing density

Dorin, Demmin, Gabel, Chemistry The Study of

Matter , 3rd Edition, 1990, page 71

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

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?

Note temperature and density units

- Page 90

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)

Density Review

- 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

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

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

- Page 91

- Page 92

End of Section 2 Measuring Matter