2. SI (Systeme Internationale) System of units
Fundamental units
A quantity that cannot be measured in a
simpler form
Quantity Unit
Distance Meter
Mass Kilogram
Time Seconds
3. Units are standardized and regulated by two
organizations:
International Bureau of Weights and
Measures (France)
National Institute of Science and Technology
(Maryland)
All measurement tools are calibrated using the
standards stored at these locations
4. Standard Unit Definitions
• Meter
1790 – 1/10,000,000 the distance from the north pole to the
equator, measured along a line passing through Lyons, France
1875 – The distance between two lines engraved on a platinum-
iridium bar stored in Paris
1984 – the distance traveled by light in a vacuum during a time
interval of 1/299,792,458 s
5. Standard Unit Definitions
• Second
old – 1/86,400 of the mean solar day
new – the duration of 9,192,631,770 periods of the
radiation corresponding to the transition between the two
hyperfine levels of the ground state of the cesium atom
(the vibration of the cesium atom in an atomic clock)
6. Standard Unit Definitions
• Kilogram
1790 – mass of exactly one cubic decimeter of water
1899 – mass of the international prototype of the kilogram
This apple sized piece of platinum-
iridium protected behind glass in
Paris is the definition of a kilogram.
Because of contaminants and
cleaning, the mass does change ever
so slightly.
7. This is the future standard of the
kilogram.
The kilogram will soon be defined as a
specific number of silicon atoms since
atoms have a set mass that does not
change due to cleaning, etc.
The Avogadro Project has created a grapefruit sized silicon ball which
is the most perfectly spherical object ever created by man. Cost:
$700,000
They are in the process of COUNTING HOW MANY ATOMS IT
IS COMPOSED OF!
Avogadro’s number may even eventually change due to this
experiment.
8. Derived unit – a unit that is composed of
other units
Example: Newton, watt, volt
A Newton is a kg m/s2
9. Metric Prefixes
Prefix (symbol) Conversion Factor Example
Mega- (M) 106 1 MW = 106 W
kilo- (k) 103 1 kg = 103g = 1000 g
centi- (c) 10-2 1 cm = 10-2 m = 0.01 m
milli- (m) 10-3 1 mL = 10-3 L = 0.001 L
micro- (µ) 10-6 1 m s = 10-6 s = 0.000001 s
10. A desk was measured to be
62.52 cm tall. How many
millimeters tall is this desk?
The world's largest strawberry
was measured to be 231 g. How
many kilograms is this?
11. Factor Label Converting
When we convert units that are not metric system
based (ex: feet, inches, miles, etc) we have to use
conversion factors.
1 mile (mi) = 1609 m
1 inch (in.) = 2.54 cm
2.2 pound (lb) = 1 kg
1 lb = 454 g
1 mL = 1 cm3
1 gallon (gal) = 3.785 L
1 gal = 8 pints
12. When factor label converting, we make fractions
(ratios) out of the conversion factors so that the
original unit cancels out and the new unit remains:
Example:
According to the Guinness Book of World Records
(2008), a man from London balanced a 352 lb car (a
Mini) on his head for 33 seconds. What is the mass
of this car in kilograms?
160 kg
13. Usain Bolt ran the 100-m race at the
Beijing Olympics in a world record
time of 9.69 seconds. His average
speed was 10.3 m/s.
How fast was he running in miles per
hour?
23 mi/hr
14. The speed of sound is 330 m/s. How
fast is this in miles/hour?
15. An acre, which is 43,560 ft2, is an
area unit often used to describe the
size of a farm. What is the size of a
600 acre farm in square miles?
16. Factor Labeling
1)When a woman turns 100 years old, how any seconds has she lived?
2)If one Deutschmark (the West German unit of currency) is worth 40 cents and gasoline costs
1.30 Deustchmarks per liter, what is its cost in dollars per gallon?
3)The gasoline consumption of a small car is 17 km/l. How many miles per gallon is this?
4)The speed limit on a highway in Lower Slobbovia was given as 150,000 furlongs per fortnight.
How many miles per hour is this? (One furlong is 1/8 mile and a fortnight is 14 days. A furlong
originally referred to the length of a plowed furrow.)
5)A speed limit sign on a Canadian road reads “80 km/h.” What is this limit in miles per hour?
7)An acre, which is 43,560 ft2, is an area unit often used to describe the size of a farm. What is the
size of a 600 acre farm in square miles?
8)A football field is 120 yd long by 53 yd wide. What is the size of a football field in acres?
17. The Googol
Physicists, mathematicians and others
often deal with very large numbers.
The number 10100 has been given the
name googol by mathematicians. Let’s
compare some large numbers in physics
to the googol.
18. Approximately now many atoms make up
the earth? For simplicity, take the average
atomic mass of the atoms to be 14 g/mole.
Mass of Earth = 6 x 1024 kg
2.58 x 1050 atoms
19. Approximately how many neutrons are
in a neutron star? Neutron stars are
made up of neutrons and have
approximately twice the mass of the sun.
Mass of sun = 1.99 x 1030 kg
Mass of neutron = 1.675 x 10-27 kg
2.38 x 1057 neutrons
20. In one theory of the origin of the universe, the
universe at a very early time had a density (mass
divided by volume) of 1015 g/cm3, while it radius
was approximately the present distance of the
earth ot the sun. Assuming 1/3 of the particles
were protons, 1/3 were neutrons and the
remaining 1/3 were electrons, how many particles
made up the universe?
Distance of earth to sun = 1.49 x1011 m
Mass of proton = 1.673 x 10-27 kg
Mass of electron = 9.11 x 10-31 kg
4.12 x 1078 particles
21. Googol fun facts:
A googolplex is a 1 followed by a googol of
zeroes.
The word googol was invented in 1938 by the nine
year old nephew of mathematician Edward Kasner.
The name of the website Google is a misspelling of
the word.
Q: Who shops at the Googolplex Mall?
A: Phineas and Ferb
