Chapter 2
Equipment and Measurement
ALABAMA 8TH GiADE SCIENCE STANDARDS COVERED IN THIS CHAPTER INCLUDE:
1
Identify steps within the scientific process.
.
Measuring dimension, volume and mass using Systëme International
d’Unités (SI Units)
SCIENTIFIC MEASUREMENT
Scientists often make measurements to quantify a certain phenomenon observed in the
world around them.
Let’s say that Tariq’s teacher has asked him to measure the length
ofthe classroom. How would he do it? There are a few important
points to remember:
All measurements must have a unit. If Tariq measures the
length ofhis classroom and announces that it is 16.7, it
doesn’t mean much. Yards, meters, feet? We need a unit.
. All units must be common. What if Tariq tells us that the
room is 16.7 lengths of his feet? Great. Now we have to
measure Tanq s feet in order to denve the length of the
Tariq
room.
All units must be common everywhere. Tariq finally gets it
I
together and tells us that the room measures 1 6.7 standard feet. Well, now we
know the length ofthe room, but no one in Japan or Germany will understand the
measurement, because the rest of the world uses the metric system.
The United States has been a bit slow to comply, but metric units are now increasingly
used in this country. Let’s look at the units and equipment appropriate to a few common
measurements in the lab.
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g
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Equipment and Measurement
THE RIGHT TOOLS FOR THE RIGHT JOBS
No matter how good your procedure is, it is not worth much ifyou cannot collect any data from
it. The measurements that you make are your data. In order to make the measurements, you
need the right tools. Ifyou are in doubt about this, consider the following scenarios:
trying to paint your nails with a paint roller
washing the car with a Brillo® pad
.
using a can of soup to hammer in a nail
These are silly examples, but that is only because you know exactly what tool to use to paint
your nails, wash the car or hammer in a nail. You are learning the process of science now, and
some tools will be unfamiliar to you at first. So, we will start with three basic tools: the meter
stick, the balance and the graduated cylinder.
.
.
.
LENGTH
In this investigation, you used a
0
1
2
3
4
5
meter stick to measure the
Inches
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I
height from which the ball was
dropped and how high it
Figure 2.1 Meter Stick bounced. A meter stick is the
0
2
perfect tool for measuring
linear (straight-line) distances. Meter sticks measure
Figure 2.2 Meter Stick
distance in basic metric units called meters.
Sometimes you need a smaller tool than the meter stick. Then you may use a ruler. Rulers are
usually marked in fractions ofmeters, called centimeters, and also in inches.
‘
__;-____
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I
—
-----
Centimeters and inches are different kinds ofunits. A centimeter is 1/10 of a meter; an inch is
1/12 of a foot. Meters are a unit defined by the International System (SI) to measure the
distance dimensions (length, width and height) ofan object. One meter equals about three U.S.
Customary System feet. SI units are used by scientists all over the world, instead of regional
units like the U.S. Customary system (which is also known as English units). This makes it
easier for scientists to compare data without converting the units.
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CD
c.1
CD
CD
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MASS
Now let’s change our thinking a bit and consider how
you could expand the bouncing ball investigation.
Let’s say you wanted to compare bounces of
similarly sized balls that had different masses. When
you modify the experiment, you might also need to
change the tools you use. To measure mass, you use
a balance.
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Figure 2.3 Triple-Beam Balance
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Chapter 2
Balances measure mass in units called grams. They are different than grocery store scales,
which measure in ounces and pounds (U.S. Customary System units). Figure 2.3 shows a triplebeam balance, which is a great tool. The analytical balance is even more accurate, and it has a
digital display that tells you the mass to 4 decimal places.
VOLUME
Now let’s say we wanted to compare how much space
is taken up by several types of balls Here, we are
comparing their volumes We use a tool called a
graduated cylinder to measure volume Liquid
volume is measured in SI units called liters
The best way to measure volume using a graduated
Figure2.4 GraduatedCylinder
cylinder is to get at eye level with the numbers printed
on its side. Don’t look at the cylinder from a position above or below the cylinder, because the
volume will appear different than it actually is. Looking directly at the cylinder, as in Figure
2.4, will allow you to read the volume ofthe liquid properly. Sometimes the surface ofthe liquid
will appear curved. This is called the meniscus. If the meniscus is curved upward like a smile,
the volume is read from the lowest part ofthe curve. This is the case with water and most other
liquids, and is shown in Figure 2.4. Ifthe meniscus curves downward like a frown, the volume
is read from the top of the curve.
So, the meter, gram and liter are the three base units ofthe SI system. Table 2. 1 compares these
units with their U.S. Customary System counterparts.
Table 2.1 English-Metric Conversions
English
1 inches (in)
3.281ft
F..
Co
CD
Co
Co
C?
O.035oz
1 lb
0
0.
D
33.Sfloz
igal
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0
z
0
Metric
Length____________________
=
2.54 cm
—;-— im
Mass
—;-- ig
0.453 kg
=
Volume
1L
3.78L
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Challenge Activity
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0,
Many products in your home list both the English and metric units. Go on a scavenger hunt
and collect one item from each room. Describe the item you find and list both the English and
metric units found on its label.
Kitchen
Bathroom
Family room
0.
0
0
29
Bed room
Garage
II
Equipment and Measurement
CHANGING THE MAGNITUDE
The SI system is also called the metric system. This term is probably familiar to you. Metric
system units are defined in multiples of 10 from the base unit. The metric prefixes indicate
which multiple of 10
10, 100 or 1,000
the base unit should be multiplied or divided by.
The table below is set up to help you know how far and in which direction to move a decimal
point when making conversions from one unit to another.
—
—
Table 2.2 Changing the Magnitude of a Unit
.
Prefix
Abbreviation
Multiplication
factor (from the
base unit)
kilo
(k)
hecto
(h)
deka
(da)
Base Unit
deci
(U)
centi
(c)
milli
(m)
km
hm
dam
meter
dm
cm
mm
icE
hL
daL
Liter
dL
cL
niL
kg
hg
dag
gram
dg
cg
mg
1000
100
10
1
0.1
0.01
0.001
.
Multiply when changing from a larger unit to a smaller one. Divide when changing from a
smaller unit to a larger one. (Remember, dividing is the same as multiplying by a fraction.) Let’s
look at two examples.
Let’s say you have a bowling ball with a mass of4.54 kilograms (kg). To convert kg to grams
(g), move three spaces to the right on the table. Each ofthose spaces represents a multiplication
factor of 10. Since 10 x 10 x 10 =1000, you multiply by 1000.
4.54 kg x 1000 = 4,540 kg
Here’s another example. A soda can has a volume of 355 milliliters (niL). To convert mL to
deciliters (dL), you move two spaces to the left. Since 10 x 10 = 100, you divide by 100, which
is the same as multiplying by 0.0 1
.
355mL÷l0O=355mLx0.O1=3.55dL
Some abbreviations, like the deciliter (dL), may be unfamiliar to you. In the science lab, and in
most real-life applications, kilo-, centi- and milli- will be the abbreviations that you most often
encounter. However, all these units are correct, and some of the lesser-known ones are even
common in particular industries. The hectometer (hm), for instance, is a commonly used unit
in agriculture and forestry.
Chapter 2
IE
Activity
The best way to get used to changing the magnitude ofthe units is to practice
doing so. Use the problems below to help you begin practicing.
,L
42
kg
x
2.
33
cm
÷
m
3.
86
mL
÷
L
4.
2.43
mg
÷
g
5.
11
hm
x
m
6.
23.1
mm
÷
km
7.
32
L
x
mL
8.
76
kg
x
mg
9.
6.7
dL
x
mL
10.
44
mm
÷
cm
11.
171
iii
÷
km
12.
1.20
g
÷
kg
13.
246
g
x
mg
14.
2.2
cm
x
=
mm
15.
196
mm
÷
=
cm
16.
20.0
dL
÷
=
L
17.
117
hm
÷
=
km
18.
215
hm
x
=
m
19.
16.3
m
÷
=
km
20.
20
L
x
=
cL
21.
1
kg
x
22.
4.2
kg
x
23.
163
g
÷
24.
1.56
km
x
=
m
25.
70
m
÷
=
km
26.
42
L
x
=
27.
9
mL
÷
=
28.
29
dm
÷
=
29.
22.2
mg
÷
=
!
=
g
cg
=
g
kg
0
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L
.
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cg
Equipment and Measurement
CHAPTER 2 REVIEW
1. Kilograms are a unit ofmeasurement for
A
B
C
B
mass.
height.
volume.
size.
2. Identify the correct conversion of4.2 grams (g) to kilograms (kg).
A
4.2g=O.0042kg
B
4.2g=O.042kg
4.2g=42kg
C
B
4.2g=4,200kg
3. Why do scientists from countries around the world use the same measurement
system?
A
B
C
B
to simplify international patent laws
to simplify the laws of physics
to make it easier for scientists to misrepresent their results
to make it easier to understand and compare published results
4. Graduated cylinders are marked in units of
A
B
C
B
5.
grams.
meters.
millimeters.
milliliters.
Identify the most accurate length of the leaf in the figure below.
345
inches
•
•
1 I
:••••>•
I
I :.;
I
Centimeters
A
B
C
B
.
3.Oinor5.9cm
2.8mor7.Ocm
2.5inor6.2crn
2.0 in or 5.5 cm
a)
2
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