Transcript chapter 1 -measurement

CHAPTER 1 MEASUREMENT
Working With Measurements
pp. 18 - 22
VOCABULARY
1.
2.
3.
Significant digits – meaningful digits in
a measured quantity
Accuracy – how close a measurement
is to an accepted or true value
Precision – describes how close
together or reproducible repeated
measurements are.
VOCABULARY
4.
5.
Resolution – refers to the smallest
interval that can be measured
Significant difference – two
measurements are only significantly
different if their difference is much
larger than the estimated error.
PRECISION VS. ACCURACY
Dart Game:

Hitting the bulls eye is an
example of accuracy.

People may demonstrate
precision by throwing a
group of darts close
together, even though
they may not be close to
the bulls eye.
Two Types of Numbers
Exact Numbers – Values are known exactly that
have defined values or are integers obtained
by counting.
Example: 2.54cm/inch, 12 inches/foot, 6
moles of iron atoms
Inexact Numbers – Values that have some
uncertainty
Numbers obtained by measurement
When measuring, the last digit is uncertain.
All digits including the uncertain one are called
significant figures (or significant digits)
The number of significant figures indicates the
exactness of a measurement.
Exact numbers theoretically have infinite significant
digits!!!
Rules for Counting Significant
Digits (a.k.a. SigFigs)
Non-zero integers always count as significant.
32.7 cm
3 sigfigs
3.7 g
2 sigfigs
1421 km
4 sigfigs
2. Zeros
A. Captive zeros are ALWAYS significant
307cm
3 sigfigs
1.007mg
4 sigfigs
1.
Rules for Counting SigFigs
(cont.)
B.
Leading zeros are NEVER significant
0.0025 mol
2 sigfigs
0.0264 g
3 sigfigs
C.
Trailing zeros at the right end of a number ARE
significant only if there is a decimal point.
100cm
1 sigfig
100.cm
3 sigfigs
100.0cm
4 sigfigs
1200cm
2 sigfigs
2.56 x 107cm 3 sigfigs
Rounding Rules
If a digit is to be removed…
1.) Less than 5; preceding digit remains same.
2.) Equal to or greater than 5; preceding digit is
increased by 1.
1.36  1.4
6.28  6.3
BOX AND DOT METHOD
1.
2.
3.
Draw a box around all nonzero digits ,
beginning with the leftmost nonzero digit
and ending with the rightmost nonzero digit
in the number.
If a dot is present, draw a box around any
trailing zeros.
Consider any and all boxed digits
significant.
SIGNIFICANT FIGURES
 Read
Significant Figures
WS and then Complete
SigFigs WS
RESOLUTION
RESOLUTION
Find out the
resolution of your
digital camera (if
you own one).
 What does
“megapixel”
mean?
