Scientific Measurement Review
Physics 1st Six Weeks
An appetizer to start…
What the TEKS say…
§112.39. Physics
(c) Knowledge and skills.
(2) Scientific processes. The student uses a systematic
approach to answer scientific laboratory and field investigative
questions. The student is expected to:
(H) make measurements with accuracy and precision and
record data using scientific notation and International System
(SI) units
What the law says…a history lesson
• In 1866, the “Metric Act” was signed into law by President Andrew Johnson
legalizing the use of the metric system.
• 1975 President Gerald Ford signed the “Metric Conversion Act” into law and It
declared the Metric System "the preferred system of weights and measures for
United States trade and commerce”, but permitted the use of United States customary
units in non-business activities.
• The legislation was sponsored by Rep. Olin Teague of Temple, Texas who was the
Chairman of the US House Subcommittee that oversaw the manned missions to the
Moon.
• 1988, the “Trade and Competitiveness Act” required federal agencies to use the
metric system
• By the way, “customary units” are better known as the “English System” or
“Imperial System” of miles, quarts, gallons, feet, inches, pounds, cups, ounces, etc.
What is the metric system?
• The first standardized system of measurement, based on the decimal
was proposed in France about 1670.
• It was created to develop a unified, natural, universal system of
measurement.
• In 1790 King Louis XVI of France assigned a group to begin this task.
• At that time, every country had their own system of weights and
measures. England had three different systems just within its own
borders!!
• In fact if you look up an old land document in Texas (or other parts of
the US that used to be part of the Spanish Empire) you’ll see land
measured in a Spanish unit “Varas” which were about 33.3 inches or
0.85 m long.
• It was called the "metric" system, based on the French word for
measure.
• As of 2005, only three countries, the United States, Liberia, and
Myanmar, have not changed over to the metric system.
• The official modern name of the metric system is the International
System of Units or abbreviated SI.
Behold! The countries of the world that
still use the English System*
*They’re the ones in red – Burma, Liberia, & The United States
according to the “CIA World Fact Book” (accessed 9/13/2015)
https://www.cia.gov/library/publications/the-worldfactbook/appendix/appendix-g.html
What the law says…and an example of why
we have to catch up
• The problem is that all the acts passed thus far have been voluntary on the part of the
States, counties, and the public. (The only exception is the FDA which requires dual
labelling)
• But as the world has increasingly gone metric and the US must strive to stay
competitive in industry, science, and business – soon will come the time when it will
be mandatory.
• Not converting has its costs. In 1999, NASA lost $125 million when its Mars
Climate Orbiter (what was to be the first weather observer on another world) was
destroyed after its altitude-control system mixed up U.S. customary units with metric
units.
“A NASA review board found that the problem was
in the software controlling the orbiter’s thrusters. The
software calculated the force the thrusters needed to
exert in pounds of force. A separate piece of software
took in the data assuming it was in the metric
unit: Newtons.”
The Metric System
• All measurements must have a number and a unit to make sense
(Example: 150 cm).
• Also to avoid confusion, never leave a naked decimal point – cover
it up with a zero!
• In the United States, the most widely used standards of
measurement are the English and the Metric System.
• The US is currently the only country in the world who still makes
routine measurements using English units (feet, miles, gallons,
etc.). Myanmar & Liberia claim they are in the process of
converting.
• However, Science worldwide uses the Metric System for taking
measurements.
• Another term for Metric Units are SI Units (from the French
“System Internationale” or “International System”)
•
The Metric System
System
The metric system is based on a base unit that
corresponds to a certain kind of measurement
• The unit is known as a base unit and prefixes are added
to show different multiples of the base unit
•
•
•
•
•
•
Length = meter (m)
Weight or Force = Newton (N)
Volume = Liter (L)
Energy = Joule (J)
Mass = gram (g)
Pressure = Pascal (Pa)
Power = Watt (W)
Note: Certain symbols for some bases are capitalized.
In the case of the Liter it is capitalized when by itself only, that is to
avoid the l being confused with a 1 (see they look alike, right!).
• The bases Watt, Joule, Newton, and Pascal are capitalized with or
without a prefix, since they were named for people.
Metric Units (aka “Bases”)
Prefixes plus base units make up the metric system
Example:
Centi + meter = Centimeter (which is 0.01x the meter)
Kilo + Liter = Kiloliter (which is 1000x the Liter)
*Note: without a prefix YOU ONLY HAVE A BASE
Common Small Prefixes
• nano – one billionth, symbol n
• micro – one millionth,
symbol μ
• milli – one thousandth,
symbol m
• centi – one hundredth,
symbol c
• deci – one tenth, symbol d
Common Large Prefixes
• Tera – Trillion times the base unit,
symbol T
• Giga – Billion times the base unit,
symbol G
• Mega – Million times the base,
symbol M
• kilo – 1000 times the base, symbol k
• hecto – 100 times the base, symbol h
• deca – 10 times the base, symbol da
Metric System…odds & ends
• Derived Units – are units that are mathematical
combinations of other units.
•
•
•
•
•
Common Metric Examples include:
Density (which is mass ÷ volume) = g/ml or g/cm3
Pressure (force ÷ area) = N/cm2
Speed (distance ÷ time) = cm/sec or km/hr
Momentum (mass x speed)= kg * cm/sec
• Note: 1 mL = 1 cc = 1 cm3
What is the order of the common metric
prefixes?
• King Henry Died By
Drinking Chocolate Milk
–
–
–
–
–
–
–
King: kilo
Henry: hecto
Doesn’t: deca
Usually: unit (m, L, g)
Drink: deci
Chocolate: centi
Milk: milli
Note: In the SI System, the symbol for the prefix is added to the
Symbol for the unit – so that to show hundredths of a meter you’d
Use (hundredth) + (meter) or centimeter
Converting within the Metric System
• For each “step” to right,
you are multiplying by 10
• For example, let’s go from a base unit to centi
1 Liter = 10 deciliters = 100 centiliters
• For each “step” to left,
you are dividing by 10
2 grams = 0.2 decagrams = 0.02 hectograms
kilo
hecto
deca
meter
Liter
gram
deci
centi
Note: There
are no
fractions in
the SI
System!
milli
Metric System
• Moving to the right, moves the decimal to the right.
• Now let’s start from meters and convert to centimeters
5 meters = 500 centimeters
kilo
hecto
deca
meter
Liter
gram
deci
centi
milli
• Now let’s start from kilometers and
convert to meters
0.3 kilometers = 300 meters
kilo
hecto
deca
meter
Liter
gram
deci
centi
milli
Metric System
• Moving to the left, moves the decimal to the left
• Now let’s start from meters and convert to kilometers
4000 meters = 4 kilometers
kilo
hecto
deca
meter
Liter
gram
deci
centi
milli
• Now let’s start from centimeters and
convert to meters
4000 centimeters = 40 meters
kilo
hecto
deca
meter
Liter
gram
deci
centi
milli