2. METRIC SYSTEM AND MEASUREMENT

2. METRIC SYSTEM
AND MEASUREMENT
Measuring the world around you
OBJECTIVES
Figure 2.1
Standard units of the metric system
At the end of this lab, you should be able to:
Measure
Unit
Example
1. Identify the standard units of the metric system and make
Length
Meter (m)
Height of a typical door handle
conversions among units.
2. Measure using metric system units.
INTRODUCTION
(1 m = approx. 39 inches)
Mass
Gram (g)
Mass of one dollar bill
(1 g = 0.035 oz)
Volume
Liter (1)
The purpose of this exercise is to introduce the metric system.
Volume of large fast food soda
( 1 1 = approximately 1 quart)
To conduct a scientific investigation, a researcher must be
Temperature Celsius (°C) Water freezes at 0°C and boils at
able to make accurate measurements. In today's exercise you
will become familiar with metric system units and converting
100°C
or subunit prefix. Superunits contain Greek prefixes to show
between large and small metric units. In each of the sections
multiples of the base unit, so they make the base unit larger.
that follow, you will first familiarize yourself with the appro-
Latin prefixes, on the other hand, represent subunits that
priate metric unit until you have a "feel" for its size, then you
make the base unit smaller.
will estimate the measurements of some everyday objects.
Finally, you will measure the objects to see how close your
B. METRIC CONVERSIONS
Conversions within the metric system can be made easily
using a metric staircase. Each step of the staircase represents
a ten-fold change in the value of the measure or a shift of the
decimal point one place. Therefore, each step you move down
The International System of Measurement (SI), commonly
the staircase represents multiplication by ten or a movement of
called the metric system is used by scientists worldwide and
the decimal one place to the right. Each step up the staircase
has been adopted as the official system of measurement by
represents a division by ten or the movement of the decimal
most countries. Unlike our
point one place to
Figure 2.2
the left. Two steps
traditional system of meaCommon metric system prefixes and their values
up or down the
surement (inch, foot, yard,
Prefix Symbol Value
staircase
represents
mile), the metric system
Superunit Kilo
K
Thousand 1000.0
IO 3
a movement of the
Hecto h
Hundred
100.0
IO 2
is based on standard units
decimal point two
Deca
da
Ten
10.0
10
that can be easily converted
places to the left or
Unit
Meter m
One
1
1.0
by simply multiplying
right and three steps
Gram g
or dividing by ten. The
up or down the
Liter
1
staircase
represents
standard metric unit for
Subunit
Deci
d
Tenth
0.1
io-12 a movement of the
length is the meter. Gram
Hundredth
0.01
io-3
Centi c
Milli
m
Thousandth
0.001
io-6 decimal point three
is the standard unit of
Millionth
Micro u
0.000001
io-9 places to the left or
mass and liter the standard
Billionth
0.000000001 ioNano n
right. Your instrucunit of volume. Scientists
tor will demonstrate
measure temperature in degrees Celsius (or Kelvin).
how to make conversions within the metric system using the
Measurements are further expressed using a superunit prefix
staircase.
estimates were.
A. METRIC UNITS
2. METRIC SYSTEM
Figure 2.3
The Metric Staircase
Move decimal
point to the
left.
Meter, liter or gram
Move decimal
point to the
right.
C. MEASURING
On your laboratory table, you will find several measuring
instruments such as a meter stick, graduated cylinder, balance
and thermometer. Familiarize yourself with these tools. Your
instructor will demonstrate how each is properly used.
Obtain a wooden meter stick (1 meter in length) and a plastic
1. LENGTH
metric ruler. Spend a few minutes looking at the meter stick
The basic unit of length in the metric system is the meter
and the ruler. Try to memorize how big the meter stick is,
(m). Common derived units are the centimeter (cm) (10~2 or
and how big the centimeters and millimeters on the ruler are.
1/100 of a meter) and the millimeter (mm) (10'3 or 1/1000
Now estimate the sizes of the objects below. After you have
of a meter). For measuring large distances, the kilometer (103
recorded each estimate, measure the object and see how close
or 1000 meters) is often used.
your estimate was.
Estimate;
Measurement:
Width of door (meters)
m
Length of chalkboard (meters, entire board)
m
Length of a dollar bill (centimeters)
cm
Width of your pen (millimeters)
mm
Thickness of a dime (millimeters)
mm
Which of your fingernails is closest to 1 cm in width?
2-2
m
mm
2. METRIC SYSTEM
2. VOLUME
The volume of solid objects (like rocks, for example) can
be obtained by measuring how much water they displace
in a beaker or graduated cylinder. To measure the volume
of an object using this method, first partially fill a beaker
or graduated cylinder with water. Record the volume of
water. Next, submerge the object completely under the
water. Use extreme care when placing the object into the
beaker as to avoid breaking the glass. The increase in the
water's volume is equal to the object's volume. Hint: Use
as small a beaker as possible for your object. The smaller
the beaker, the more accurate your measurement will be.
The basic unit of volume in the metric system is the liter (1).
The most common derived unit is the milliliter (ml) (10~3 or
1/1000 of a liter). The volume of a milliliter is equal to the
volume of a cube 1 centimeter per side. Another derived unit
is the micrometer (ul) (ID" 6 or 1/1,000,000 of a liter).
View the 1 liter of water (in the soda bottle) and the 1 ml
plastic cube. Spend a few minutes memorizing the volumes
of 1 liter and 1 milliliter before you begin to do the volume
estimations on the next page.
When you are doing the volume estimations,
how do you measure the actual volumes of
the objects you have estimated?
40
Meniscus
To measure the volume of a liquid,
it is usually poured into a beaker or
cylinder with measurement marks (or
"graduations" as they are sometimes
called). The top of the liquid forms a
slight curve, called a "meniscus". The
volume of the liquid is the graduation
closest to the bottom of the meniscus.
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Very small volumes of water can be accurately measured
using a scale, because each milliliter of water weighs 1
gram. To measure water this way, first put a small beaker
on the scale, "zero" the scale by pressing the tare button
(O/T on our scale). Be sure the readout shows a little "g"
after the zero. If it says "N" the reading is not in grams.
Now add the water to the beaker. Each gram that the
scale reads equals 1 ml of water.
Now estimate the volumes of the liquids and objects listed
in the table below. It helps to hold the 1 ml cube or the liter
bottle next to the object while estimating its volume. After
you have recorded each estimate, measure the volume and see
how close your estimate was.
Object:
Estimate:
Measurement:
Water in clear bottle on front desk
(use a graduated cylinder to measure; refill the bottle when you are done)
Water in full cup (use graduated cylinder)
ml
Water in glass vial (use a small beaker)
il
il
How many drops does it take to equal 1 ml? To find out, add drops, counting one at a time, to a 10 ml graduated cylinder.
Stop when the water reaches the 1 ml mark on the cylinder.
Drops per 1 ml =
ml per one drop =
Medium rock*
(milliliters)
Large rock*
(milliliters)
(* Write the letter of each of your rocks in the blank space)
ml
2. METRIC SYSTEM
3.
may take a moment to zero itself. (The zero should have a "g"
after it for grams). Lastly, place the object in the container
The basic unit of mass in the metric system is the gram (g).
and read its weight.
3
The most common derived unit is the milligram (mg) (10" or
1/1000 of a gram). For measuring large masses, the kilogram
3
(10 or 1000 grams) is often used.
If the mass of an object and the volume of the object are
both known, the density of the object can be calculated. The
formula for density is simply the object's mass (in grams)
Obtain the box of metric weights from the counter. Spend a
divided by its volume (in ml). For example, a 76 gram piece
few minutes holding the various weights in your hand to get
of gold might have a volume of 4 milliliters. The density of
a feel for a kilogram, 500g, 200g, Ig, etc. When done, please
gold is therefore:
replace the box for the next group to use.
(76 grams) / (4 milliliters) = 19 grams per milliliter
Masses are measured by using a scale. Before you weigh
anything, first place a container to hold the object (for
Estimate the masses of the objects below. After you have
example, a beaker to hold water if you are weighing water or
recorded each estimate, measure the object and see how close
a pan if you are weighing a solid). Next, press the tare button
your estimate was.
(labeled O/T on our scale) to reset the scale to zero. The scale
Estimate:
Measurement:
Nickel (grams)
Penny (grams)
The weight of one person from your group (kg)
(Don't step on our scale! Ask me for a conversion factor)
Medium rock* (grams)
Large rock* (kg)
* Use the same two rocks you used in the volume section.
.kg
.kg
What is the density in grams per milliliter (g/ml) of each rock? (Section 2 must be completed to answer this question).
Medium rock = _
g/ml
Large rock =
What is the density in grams per milliliter (g/ml) of each rock? (Section 2 must be completed to answer this question).
Medium rock = _
g/nil
Large rock = _
Would the density of these rocks be different if you had used a larger piece of the same rocks?
2-4
g/ml
_
2. METRIC SYSTEM
4, TEMPERATURE
REVIEW QUESTIONS
The basic unit of temperature in the metric system is the
degree Celsius. (°C ). There are no commonly derived units.
1) Convert the following values into the new units. Use the
unit factor method and show all your work.
To get a feel for degrees Celsius, consider the following
temperatures:
•
•
•
•
8 meters =
mm
22.1 ml =
1
g
Ice water and the freezing point of water are 0°C
0.00003 m =
mm
Room temperature water are 20 — 25°C
10,900 cm =
m
57 mm =
0.0034 mg =
g
0.98 kg =
ul
349 ml =
cm
Normal body temperature is 37°C
mg
Water gets too painful to touch between 50 — 60°C
0.0087 1 =
•
0.98 kg -
ul
Water boils at 100°C
6602 =
mg
4590 ul =
ml
With the above temperatures in mind, estimate the temperatures of the four water baths by placing your finger in each
one for a few seconds. Don't look at the thermometers until
2) How many grams does 73 ml of pure water weigh?
after you have made your estimates.
Object (° Celsius):
Estimate:
Measurement:
3) What is the volume of 0.23 kg of pure water?
o g~~*
o S~~*
Water in beaker B
°c
°C
Water in beaker C
°c
0
Water in beaker D
°c
Water in beaker A
C
C
4) Pure gold has a density of 19 g/ml. If you bought a "gold"
C
ring and found it had a volume of 0.3 ml and that it weighed
5.7 grams, is it real gold?
O
f~^
C
2-5