Units
and
Measurement
Physics
Mr. Austin
International Space Station
http://apod.nasa.gov/apod/image/0706/iss_sts117_big.jpg
What is Physics?
• The study of the relation between energy
and matter
• The study of:
– Motion
– Heat
– Light
– Energy
– Much More!
Math and Units
• Math- the language of Physics
• SI Units – International System
– MKS
• Meter m
• Mass kg
• Time s
• National Bureau of Standards
• Prefixes
SI Unit Prefixes - Part I
Name
Symbol
Factor
tera-
T
1012
giga-
G
109
mega-
M
106
kilo-
k
103
hecto-
h
102
deka-
da
101
SI Unit Prefixes- Part II
Name
Symbol
Factor
deci-
d
10-1
centi-
c
10-2
milli-
m
10-3
micro-
μ
10-6
nano-
n
10-9
pico-
p
10-12
femto-
f
10-15
SI Unit Prefixes for Length
Name
gigameter
megameter
kilometer
decimeter
centimeter
millimeter
micrometer
nanometer
picometer
Symbol
Gm
Mm
km
dm
cm
mm
μm
nm
pm
109
106
103
10-1
10-2
10-3
10-6
10-9
10-12
The Seven Base SI Units
Quantity
Unit
Symbol
Length
meter
m
Mass
kilogram
kg
Temperature
kelvin
K
Time
second
s
Amount of
mole
Substance
Luminous Intensity candela
mol
Electric Current
a
ampere
cd
Derived SI Units (examples)
Quantity
unit
Symbol
Volume
cubic meter
m3
Density
Speed
kilograms per
kg/m3
cubic meter
meter per second m/s
Newton
kg m/ s2
N
Energy
Joule (kg m2/s2)
J
Pressure
Pascal (kg/(ms2)
Pa
Scientific Notation
Mx
n
10
• M is the coefficient 1<M<10
• 10 is the base
• n is the exponent or power of 10
Other Examples:
• 5450000 = 5.45E+6
or 5.45 x 10^6
Numbers less than 1 will have a
negative exponent.
A millionth of a second is:
0.000001 s or 1x10-6 s or 1.0E-6
s
Write in Scientific Notation
• 3250 =
– 3.250 x 103
• .000435 =
– 4.35 x 10-4
• 425620000 =
– 4.2562 x 108
Factor-Label Method of Unit
Conversion
• Example: Convert 5km to m:
• Multiply the original measurement by a
conversion factor.
NEW UNIT
85km x 1,000m
1km
OLD UNIT
=
85,000m
Factor-Label Method of Unit
Conversion: Example
• Example: Convert 789m to km:
789m x 1km =0.789km= 7.89x10-1km
1000m
Convert 75.00 km/h to m/s
75.00 km x 1000 m x 1 h___ = 20.83m/s
h
1 km
3600 s
• Accuracy - a measure of how
close a measurement is to the
true value of the quantity being
measured.
Example: Accuracy
• Who is more accurate when
measuring a book that has a true
length of 17.0cm?
Susan:
17.0cm, 16.0cm, 18.0cm, 15.0cm
Amy:
15.5cm, 15.0cm, 15.2cm, 15.3cm
• Precision – a measure of how
close a series of measurements
are to one another. A measure of
how exact a measurement is.
Example: Precision
Who is more precise when measuring
the same 17.0cm book?
Susan:
17.0cm, 16.0cm, 18.0cm, 15.0cm
Amy:
15.5cm, 15.0cm, 15.2cm, 15.3cm
Example: Evaluate whether the
following are precise, accurate or
both.
Accurate
Not Accurate Accurate
Not Precise Precise
Precise
Solving Word Problems
• Analyze
– List knowns and unknowns.
– Draw a diagram.
– Devise a plan.
– Write the math equation to be used.
• Calculate
– If needed, rearrange the equation to solve for the
unknown.
– Substitute the knowns with units in the equation and
express the answer with units.
• Evaluate
– Is the answer reasonable?
Practice!
• Please complete the following problems in
class. What you do not finish will be
homework to be turned in tomorrow.
• Pg. 24 #34, 36, 37, 41, 50, 51, 56, 67, 84,
85.
• Read pages 9 and 10 and answer # 49
from pg. 25
• Short Quiz Tomorrow after HW review