Transcript Diapositiva 1

Warm up: Tuesday, Aug. 19
1. Get out Ch. 1.3 Notes, turn to 1.4, have out HW Set 1-3
2. The density of an object was found by using water
displacement. The following data was collected (this is
in packet).
Mass of Object
Volume of Water
Volume of Water
and Object
24.46 g
12.5 mL
16.3 mL
(a) Determine the volume of the object.
(b) Calculate the density of the object.
RULES FOR DETERMINING
SIGNIFICANT FIGURES
• Rule #1: Nonzero digits always count as
significant figures:
Examples:
438 g
26.42 m
_____ sig fig
_____ sig fig
1.7 cm
_____ sig fig
2.653 L
_____ sig fig
• Rule #2: Captive zeros always count as
significant figures:
Examples:
506 dm
1005 mL
900.43 kg
20.006 cm
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
• Rule #3: Leading zeros do not count as
significant figures:
Examples:
0.8 g
_____ sig fig
0.06 g
0.0047 L
_____ sig fig
_____ sig fig
• Rule #4: Trailing zeros are significant only if
the number contains a decimal point:
Examples:
60 g
4830 km
8.0 dm
1.60 sec
35.000 L
0.002450 kg
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
_____ sig fig
RULES FOR ROUNDING NUMBERS
• If the digit immediately to the right of the last
significant figure you want to retain is:
• Less than 5 ------ the last significant digit
should stay the same.
Example:
Round 17.32 m to 3 significant figures.
– Since the 2 is less than 5, you should round to
__________ m
• 5 or greater --------- the last significant
figure should increase by 1.
Example:
Round 42.68 g to 3 significant figures.
– Since 8 is greater than 5, you should
round to __________ g
What Do You Think?
1)
Determine the number of significant figures in each
of the following:
a. 12.045
d. 12.0
b. 0.0028
e. 0.500
c. 6500
f. 16.002070
2)
Round each of the following to 2 significant figures.
a. 5.2836
b. 0.06382
c. 3196
3)
Explain how the measurement 6.2 cm is different
from 6.20 cm.
CALCULATIONS WITH MEASUREMENTS
• Rule #1: Whenever you add or subtract
measurements, your answer should have as
many DECIMAL PLACES as the measurement
with the LEAST number of DECIMAL PLACES.
EXAMPLE:
23.445 g + 7.83 g =
31.275 g
31.28 g
• Rule#2: Whenever you multiply or divide
measurements, your answer should have as
many SIGNIFICANT FIGURES as the
measurement with the LEAST number of
SIGNIFICANT FIGURES.
EXAMPLE:
1.342 cm × 5.5 cm =
7.381 cm2
7.4 cm2
Its Your Turn!
• Perform the following calculations and
record your answer to the correct number of
digits.
a. 14.025 – 6.49 =
b. 142.38 x 3.050 =
c. 59.968 / 0.07628 =
Scientific Notation
• Short hand for writing very large or small
numbers
• Two parts: Coefficient and Power of 10
A number between 1
and 10 (can include
1 but not 10).
Exponent:
 + exponent
 - exponent
Practice
Write the following numbers in scientific
notation:
1. 41,000
2. 0.0029
3. 60,007,000
4. 0.000 000 132
5. 123,000,000
One Minute Paper
• You have one minute to answer these two
questions concerning significant figures and
calculations with measurements.
– What was the most important thing you
learned?
– What is still muddy?