Scientific Measurement
Chapter 3
3-1 The Importance of
Measurement
• Qualitative vs Quantitative
Measurement
•What color vs What
mass?
• Scientific Notation
•Powers of Ten
3-2 Uncertainty in
Measurements
• Accuracy, Precision and
Error
• Communicate the quality of
Experimental Data and
Calculations
3-2 Uncertainty in
Measurements
• Accuracy
•How close to the
accepted value is the
measurement?
3-2 Uncertainty in
Measurements
• Precision
•How are the Data
Grouped?
–Tight vs Loose
3-2 Uncertainty in
Measurements
• Error = Accepted value –
Experimental value
• % Error =
Error
x 100%
Accepted value
Practice Problem
• Suppose you compare a
wooden meter stick to a
certified standard meter stick
and get the following data:
Practice Problem
• Length of wooden meter
stick
= 1.009 m (oops)
• What should the “accepted
value” be?
Practice Problem
• That’s right! 1.000 m
• Error = accepted –
experimental
= 1.000 – 1.009
= -0.009 m
Practice Problem
• % Error = Error x 100%
Accepted
= -0.009m  x 100%
1.000m
= 0.9 %
Significant Figures in
Measurements
• How well do you know your
data? Is it •0.8m
•0.75m
•0.753m
•0.7529m
Significant Figures
• All four measurements could
have come from the same
object measured with
increasingly precise
equipment.
•“Degree of Precision”
Significant Figures
• Significant Figures show
all digits directly
obtained in a
measurement plus the
first estimated digit.
Significant Figures
• The number of significant
figures in measurements is
governed by RULES
See pages 56 & 57
… beware the lowly zero,
it will confuse you.
Significant Figures
• Exact numbers: infinite sig
figs
• counting numbers
1 cookie, 2 cookies …
• defined quantities
1 meter = 100 centimeters
Significant Figures in
Calculations
• It’s a different game.
• You can’t know a calculated
result any more precisely
than your least precise term.
• “Weakest Link”
Significant Figures in
Calculations
• Rules governing
addition/subtraction are
–DIFFERENT
– from the rules governing
multiplication/division.
–See pages 58-61
3-3: Units
• SI = International System of
Units
–
see Table 3.1 page 63
• Base units vs derived units.
Units
• SI is related to the metric
system.
• We generally use the metric
system and its prefixes.
–See Table 3.2 page 64
Units: Length
• Meter
• Derived units:
•Area (squared)
•Volume (cubed)
Units: Volume
• Space matter occupies
• Unit cubes
3
• V= lwh = s
3
• 1 cm x 1cm x 1cm = 1cm =
1ml
• 1 liter = 1,000 ml
Units: Mass
• Amount of matter in
object
• Unaffected by gravity
• 1 ml water = 1 gram
Units: Density
• Relates mass of an object to
its volume
• Property of all matter
• Density = mass = m
–
volume
v
Units: Temperature
• SI: Kelvin scale (absolute)
•unit = K (kelvin)
• Metric: Celsius
•unit = C (degree Celsius)
• Pet peeve: There is no such
thing as a “Degree Kelvin”
Units: Temperature
• Convert from K to C
•C = K – 273
• Convert C to K
•K = C + 273