Transcript Metric System

The Metric System
“I’m ten times
better than the
Standard system
of measurement!”
Metric System
Many laboratory activities require measurements.
Science uses the S.I. (Metric System) of
measurements.
Measurements in Experiments
Metric System
• Developed by the French in the late 1700’s.
• Based on powers of ten, so it is very easy to use.
• Used by almost every country in the world, with
the notable exception of the USA.
• Especially used by scientists.
• Called the International System of Units or
in French the Le Système International
d'Unités abbreviated SI.
Metric Prefixes
• Regardless of the unit, the entire metric
system uses the same prefixes.
• Common prefixes are:
kilo = 1000
centi = 1/100th
milli = 1/1000th
pico = 1/1000,000,000,000 or 1 x 10 -12
1 meter = 100 centimeters =1000 millimeters
Length
• The SI base unit for length is the meter (m)
• Common units for length – millimeter, centimeter,
meter or kilometer
• Abbreviated (mm, cm, m, km)
Mass
• The SI unit for mass is the kilogram (kg)
• Balances are used to determine mass.
• Common units of mass: gram (g), milligram (mg),
kilogram (kg)
Your mass in Kg?
1 kg / 2.2 lbs
Triple Beam Balance
Electronic Balance
Temperature
•The Kelvin (K) is the SI unit for temperature
•Celsius (0C) is the metric unit for temperature
•O 0 Celsius = 273 K
Know the temperature at which water freezes and boils in the
3 different temperature scales:
temperature
kelvin
symbol
K
degree Celsius
degree Fahrenheit
°C
°F
boiling point of water
373.15
100.
212.
melting point of ice
273.15
0.
32.
absolute zero
0.
-273.15
-459.67
Volume
• Units of volume are derived
from units of length.
Formula:
Volume = length x width x height
• The metric units of volume are
cubic centimeters (cm3)
• A box 2 cm x 3 cm x 5cm has
a volume of __________ ?
• 30 cm3
Liquid Volume
• Graduated Cylinder used
to measure volume
• 1 cm3 of water is equal
1 milliliter (ml) of water
and 1 ml of water will
always have a mass of
one gram.
1 cm3 of anything = 1 mL of anything
Meniscus – the ‘bubble’ that
1 cm3 water = 1 mL of water = 1 gram
form on the wall of the glass.
Always read from the bottom of
the meniscus
Water Displacement
• Water displacement is
used to find the volume
of objects that are not
boxed shaped. (irregular
shaped objects)
• Example: 50-mL of water is
placed in a graduated cylinder.
• If a rock causes the level to
rise to 73-mL, the rock must
have a volume of 23-mL.
• 73 – 50 = 23 mL
To Convert Measurements use Dimensional
Analysis by multiplying by a conversion factor:
a factor equal to one.
Example: To convert 56 m to km --
56 m x 1 km = 0.056 km
1000 m
Example:
Convert 65 miles per hour (mph) to km/hr
65 mi/hr x 1.61 km/hr
1 mi /hr
= 104 km/hr
Accuracy and Precision
 Accuracy – describes how close a measurement is to the
true value of the quantity measured.
 Precision – the exactness of a measurement
 Example:
45.052 m is more precise than 45.0 m
Low Accuracy
High Precision
High Accuracy
Low Precision
High Accuracy
High Precision
So, if you are playing soccer and you always hit the left
goal post instead of scoring, then you are not accurate,
but you are precise!
Significant Figures
 Used to show the precision of a measured quantity
 Include all digits that are actually measured plus one estimated digit.
 Rules:
1) All non zero number are significant
738
= 3 sig figs
12345 = 5 sig figs
2) Zeros located between non-zero digits are significant
2012
= 4 sig figs
This measurement should be read
as 4.95 cm. This measurement has
3 significant figures.
3) Trailing zeros (at the end) are significant only if the
number contains a decimal point; otherwise they are
insignificant (they don’t count)
1.00 = 3 sig figs
549000. = 6 sig figs
549000 = only 3 sig figs
4) Zeros to the left of the first nonzero digit are insignificant
(they don’t count); they are only placeholders.
000.456 = 3 sig figs
0.052 = 2 sig figs
Rules for addition/subtraction problems
 The number of decimal places in the result equals the number
of decimal places in the least precise measurement
 Example:
7.939 + 6.26 + 11.1 = 25.299
 Answer =
3 sig figs
25.3 (rounded up)
Rules for multiplication/division problems
 The number of sig figs in the result equals the number in the
least precise measurement used in the calculation
 Example:
 Answer =
(27.2 x 15.63) ÷ 1.846 = 230.3011918
3 sig figs
230. (rounded down)
Estimating the last digit in a measurement
This measurement should
be read as 4.95 cm. This
measurement has 3
significant figures.
Reading a metric ruler correctly:
This point can be read as 1.65 cm. or 16.5 mm.
Density
• Density - the amount of matter (mass) compared to
the amount of space (volume) the object occupies.
• Density – Is a Physical Property of matter - it is a
constant, a number that does not change.
Example: Density of
Gold = 19.30 g / ml
Question: If you cut a
brick of gold in half
would the Density still
be 19.30 g/ml?
Yes…. Why?
Formula
Density = mass/volume D = M / V
• The unit for mass is grams (g), and the unit for
volume is mL or cm3 usually,
so the units for Density are g/mL, or g/cm3
Density Formula Wheel
• Formula wheels make it
easy to solve density
problems.
• Cover the property you
are trying to find, and
do what is left over.
• To find density, cover
the word density. You
have mass over volume
remaining. So divide
mass by volume to find
density!
Mass
density
volume
Density Formula Wheel
• To find mass, you cover
the word mass. You now
have density times
volume remaining.
• To find volume, cover
volume. You have mass
over density remaining,
so divide mass by
density to find volume.
Mass
density
volume
Understanding Density
• In the following illustrations, each
will
represent 1 cm3.
• Each g will represent 1 gram.
• Mass = 24g
• Volume = 8 cm3
g g g g
g g g g
3
• Density = 3g/cm
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
g
•In other words, there are 3 grams in
every cm3.
Density Problem 2
g
g
g
g
g
g
g
g
g
g
g
g
•Mass =
12 grams
•Volume = 6 cm3
•Density = 2 g/cm3
•In English we say the density of the object
is 2 grams in every cubic centimeter.
Density Problem 3
g
g
g
g g
g
g
g g
g g
ggg g
g
•Our previous problems were materials of
uniform density. They were the same stuff
throughout. But many materials are not.
Gravel is a great example.
•Mass = 16 grams
•Volume = 8 mL
•Density = 2 g/mL
Powers of Ten Interactive Tutorial
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
How to Convert Metric Units
See link below for an online calculator
http://www.onlineconversion.com/length_common.htm
•To convert to larger unit (example: meter to a
kilometer), move the decimal point to the left or
divide.
•To convert to a smaller unit (example: meter to
centimeter), move the decimal point to the right or
multiply.
Example: to convert 100 g to kilograms move the
decimal place 3 places to the left (or divide by 1000).
Answer: 0.100 kg