SYSTEM INTERNATIONAL (SI)
Is this system easier?
12 in = 1 ft
3 ft = 1 yd
5280 ft = 1 mile
2pt= 1 qt
4 qt = gal
16 oz = 1 lb
32 oz = 1 qt
e.g grains to pounds French. English>>different in each country
1780s French Academy of Science developed Metric System
• all fundamental units are defined in terms of things that are easily and accurately
reproducible
• all units can be converted into smaller or larger units by just moving the decimal point
• original standards has some errors and some were based on objects that could be lost
or destroyed. Therefore, during WW2 germans were instructed not to bomb
International Bureau of Standards--so critical to the world.
1960 Metric System needed some improvements
• proliferation of units needed to be trimmed down>>>>>created base units
• 7 base units & derived units--all changes by just moving the decimal place
ALL UNITS MUST BE DRIVED FROM THESE 7 BASE UNITS!!
1. Length (meter) - m
2. Mass-(kilogram)- kg
3. Time-(second)- s
4. Temperature-(Kelvin)-K
5. Amount of Substance-(mole)-mol
6. Electric Current-(ampere)- A
7. Luminous Intensity-(candela)-cd
• meter = distance red light travels in 1/299,792,456 of a second>>>will never change
SOME DERIVED UNITS
volume = m3
area = m2
acceleration = m/s2
Force = ma >> kg . m/s2 >>Newton (N)
Energy = F . d >> N . m>>(kg.m/s2)(m) = kg.m2/s2>>>>Joule (J)
What would be the correct SI unit for Density....g/cm3??? No---kg/m3...not practical in
the lab setting--we use the common convenient units of g/cm3 or g/ml
SI PREFIXES
Multiple 1024 1021 1018 1015 1012 109 106 103 102 101 Prefix Yotta Zetta Exa Peta Tera Giga Mega Kilo Hecto
Deka Symbol
Y
Z
E
P
T
(trillion)
G (billion)
M (million)
k
(thousand)
h
(hundred)
da
(ten)
m (base unit)
100
Fraction of a base unit:
10-1 10-2 10-3 10-6 10-9 10-12 10-15 10-18 10-21 10-24 deci centi milli micro nano pico femto atto zepto yocto d (tenth)
c (hundredth)
m (thousandth)
u (greek symbol mu)
n
p
f
a
z
y
MUST BE ABLE TO CONVERT BETWEEN UNIT WITHIN THE SI SYSTEM
SOME DERIVED UNITS:
volume = m3
speed = m/s
density = kg/m3
energy = kg m2/s2 = J
COMMON UNITS COMMONLY USED IN CHEMISTRY EVEN THOUGH THEY ARE
NO SI UNITS:
cm3, ml, L, 0C
6 COMMON PREFIXES IN THE METRIC SYSTEM
Mega = 106 kilo = 103
centi = 10-2
milli = 10-3
micro = 10-6
nano = 10-9
PRACTICE PROBLEMS
Convert 4.38 cm to meters
4.38cm to m
Factor Label Method
(4.38cm)( m/cm) >>> (4.38cm)(1m/102cm) = .0438 m
Big Guy Little Guy Method
4.38cm (little guy)
10-2 m(big guy) >>>answer is smaller .0438 m
(move decimal to left)
100
Convert 8.86cm to mm
8.86cm(big guy)
10-2 mm(little guy) >>>answer is larger 88.6mm
(move decimal to right)
10-3 Summary:
Big to small = move right
Smal to Big = move left
PRACTICE PROBLEM #1
Convert 1.35 mm to km
1.35mm 10-3
km(103) move six places >>move left
1.35mm x 10-6km = .00000135km
PRACTICE PROBLEM #2
convert 220g to kg
little guy to big guy move decimal to the left
.220kg
PRACTICE PROBLEM #3
convert 1.25L to ml
big guy little guy move decimal to right
1250 ml
PRACTICE PROBLEM #4
convert 1.2m to cm
big guy to little guy = move decimal to right
120cm
PRACTICE PROBLEM #5
3.56x108 mm to km
little guy to big guy = go left 6 decimal places
3.56x102 km
PRACTICE PROBLEM #6
convert
25cm2 to SI units
(25cm2)(1m/ 100cm)(1m/100cm) = 2.5x10-3m2
PRACTICE PROBLEM #7
Convert the density 1.0g/cm3 to SI Units
1g = 10-3 kg and (1cm3)(1m/100cm)(1m/100cm)(1m/100cm) = 1x10-6m3
The density is 10-3kg/10-6m3 = 103kg/m3
PRACTICE PROBLEM #8
Lisa ran 100m in 17.5s. What was her speed in SI Units?
d = vt
v = d/t
100m/17.5s = 5.7 m/s
PRACTICE PROBLEM #9
How many kilometers did Patrick run in 45 minutes if his speed was 12.2 km/hour
(45min)(1hr/60min) = .75hr
12.2km/hr x .75hr = 9.2km