Scientific Measurement
I.
Quantitative vs. Qualitative
A. Quantitative is a measurement. It is expressed in
numbers.
B. Qualitative is a description.
II.
Accuracy and Precision
A. Accuracy indicates the closeness of the measurement to
the actual value.
B. Precision indicates the reproducibility of the
measurement.
III.
Significant Digits or Significant Figures (sig figs)
Measurements are reported using all digits accurately known
plus a last digit that is estimated.
Rules
A digit is SIGNIFICANT if it is:
a. a non-zero.
b. a zero between non-zero digits.
205 1001 40.4
c. a zero at the end of a decimal number
11.0 700. 80.0
A digit is NOT SIGNIFICANT if it is:
a. a zeros before a non-zero
0.025
b. a zero at the end with no decimal point
300 10
Significant Figures in Calculations
1. Addition and Subtraction
Answer gets the same number of digits after the decimal as the
original number with the least number of digits after the
decimal
1.1 m
+ 10.557 m
-----------
17.20 g
- 0.5263 g
------------
2. Multiplication and Division
Answer gets the same number of total significant digits as the
original number with the least number of total significant digits
25 x 3.75 = 93.75 round to 94
8.00/2.00 =
Round answers at the end of your calculations.
IV. SI Units
Used worldwide in the scientific community.
Quantity
Length
Volume
Mass
Density
Temperature
base unit
m
m3
kg
g/cm3
K
also used
L
g/ml
o
C
Metric Prefixes
kilo
deci
centi
k
d
c
103
10-1
10-2
milli
micro
nano
pico
m

n
p
10-3
10-6
10-9
10-12
V.
Volume
the amount of space matter takes up
derived from length
v=lxwxh
liquid volume measured in a graduated cylinder
m3 L(dm3)
mL(cm3, cc)
VI. Mass
amount of matter in an object
measured on a balance
grams (g)
VII. Density
the amount of matter in a given space
density will change with temperature because volume
changes with temp.
density = mass divided by volume
m
d=
v
units: g/ml or g/cm3
VIII. Specific Gravity
compares density of a substance to density of water
has no units
density
spec. grav. =
density of water
IX. Temperature
measure of hotness or lack of heat
average kinetic energy
A. Heat Transfer
from high heat to low heat
B. Temp. affects volume
in general:
T goes up, V goes up (material expands)
T goes down, V goes down (material contracts)
H2O is an exception, solid is less dense than liquid
C. Units: Celsius and Kelvin
0 K is absolute zero, temp. where all molecular motion
theoretically stops
0 K = -273oC
o
K = oC + 273
C = K – 273
X.
Error in Measurements
Human error – biggest source
misreading the instrument
calculation errors
carelessness
Instruments
Problem Solving Techniques
1. Identify the unknown.
What is the problem asking?
2. Identify and list what is known or given.
3. Plan a solution.
Write down the equations you will need.
Draw a picture if it will help.
Write down any constants or conversion factors.
4. Do the calculation.
Plug and chug.
5. Finish up.
Are your units correct?
Does the answer have proper significant digits?
Put a box around your answer.
Check your work!
Conversions
Conversion Factors
 ratio of equivalent measurements
 fractions where the numerator and denominator
represent the same quantity, units are different
Examples:
1 dollar
100 cents
or
100 cents
1 dollar
1m
1000mm
or
1000mm
1m
 used to convert from one unit to another
 can be used to solve problems (called dimensional
analysis or factor label method)
 can be used in multi-step problems
Examples:
1. How many grams are in 15kg?
1000g
15kg x 1kg = 15000g
(kg cancel)
2. How many second are in 1 day?
24hrs 60 min 60sec
1day x 1day x 1hr x 1min = 86400 sec