EXACT NUMBERS!
Numbers determined by counting
or by definition
Ex: 6 apples, 1 teacher
1 inch=2.54 cm
IN SCIENCE…
Numbers are based on
MEASUREMENTS made in the lab.
Our data is only as good as the
measurements we make and the
instruments we use.
UNITS OF MEASUREMENT
There is one system for all scientists around the world.
We must have a standard for comparison
length – meter (m)
mass – gram (g)
time – second (s)
volume – liter (L)
Accuracy: how close a measured value is to
the actual (true) value.
Precision: how close the measured values
are to each other.
ACCURACY VS. PRECISION
SIGNIFICANT FIGURES
• Shows how PRECISE a measurement is
• Indicates the QUALITY of the instrument you use
(how sensitive or exact)
EX. Graduated cylinder vs. beaker
• When recording measurements, always estimate
one place value more than the instrument
provides.
SIG FIG RULES!
COUNTING SIGNIFICANT FIGURES
5432.1
0.00032
4004
82.0000
5 sig figs
2 sig figs
4 sig figs
6 sig figs
9
SCIENTIFIC NOTATION
Used to write really LARGE
or really small #’s
Why? To save space & time
SCIENTIFIC NOTATION RULES!
Written in the form of m x 10n
m: ≥ 1 AND <10
indicates the number of sig figs
STEPS OF THE SCIENTIFIC NOTATION
Step 1) Determine the sig figs
106,000,000 = 3 sig figs
Step 2) Determine the value of “m” using the sig figs
1.06 (remember this must be between 1 and 10)
Step 3) Add the 10’s multiplier
1.06 x 10n
Step 4) Determine the value of “n” by counting the number of
times you move the decimal in the original number to get
the value for “m”
Step 5) Determine the sign of “n” by looking at the direction
that you moved the decimal
 Move decimal to left = “n” is positive
 Move decimal to right = “n” is negative
Ex. 1) 7,801
Ex. 2) 0.00030
7.801 x 103
3.0 x 10-4
14
NOW GO THE OTHER WAY!!
Ex. 3) 3.1 x 104
Ex. 4) 4.08 x 10-6
31,000
0.00000408
15