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SI Base Units
Length
Meter
Mass
Kilogram
Time
Second
Amount
Mole
Temperature
Kelvin
Current
Ampere
Luminous intensity
Candela
What is the definition of a meter?
What is the definition of a kilogram?
What is the definition of a second?
Meter:
Original:
000
,
000
,
10
1
of distance between the north pole and the equator.
Defined 1960:
1,650,763.73 wavelengths of a particular orangered line in Krypton86
Modern (since 1983):
The distance traveled by light in
458
,
792
,
299
1
second.
Second:
The amount of time corresponding to 9,192,631,770 oscillations of a cesium atom.
Kilogram:
The mass of a particular platinumiridium cylinder (international prototype kilogram.
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View Full Document SI Prefixes
10
12
tera
T
10
9
giga
G
10
6
mega
M
10
3
kilo
k
10
0
base unit
10
3
milli
m
10
6
micro
μ
10
9
nano
n
10
12
pico
p
Standard prefixes are used for every three powers of 10.
Exception:
10
2
centi
c
This is used mostly for centimeter (cm)a common unit of length and cm
3
, a common unit of
volume.
Derived Units
There are many “derived” units which are combinations of the base units.
Area
m
2
, cm
2
Volume
m
3
, cm
3
Force
N = Newton = kg
2
sec
m
Energy
Joule = N m
=
kg
2
2
sec
m
Pressure
P = Pascal =
2
m
N
=
2
sec
m
kg
Density
3
m
kg
3
cm
g
Liter
:
Commonly used measure of volume
Liter
= 1000 cm
3
or 1 cubic decimeter (dm
3
)
What is the difference between mass and weight?
Weight
:
Equivalent to force (unit is Newtons).
A measure of gravitational attraction.
Mass
Rough definition:
Amount of matter
Better definition:
A measure of a body’s inertia.
Inertia is the resistance to change in motion (acceleration).
Significant Figures
Experimental measurements have an
uncertainty
.
The uncertainty depends on the
measuring instrument used.
Book example:
Measuring weight of grapefruits:
Bathroom Scale
Balance
Grapefruit 1
1.5 lb
1.476 lb
Grapefruit 2
1.5 lb
1.518 lb
These have the same weight to two significant figures (both are 1.5 lb)
They have different weights with four significant figures (measured by balance).
But even the
balance has an uncertainty, in this case at least ± .001 lb.
The uncertain digit is the last significant figure.
We have some knowledge (with uncertainty) of
that last significant digit.
We have no knowledge of any digit past the last uncertain digit.
A length is measured as 4.98 cm.
Assume the uncertainty is in the last digit (4.98 cm ± .01 cm).
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View Full Document How many significant figures?
That same length is converted to meters and is now 0.0498 meter.
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This note was uploaded on 04/03/2008 for the course GENERAL CH 162 taught by Professor Kimmel during the Spring '08 term at Rutgers.
 Spring '08
 Kimmel

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