Transcript Friction: What you need to know!

Measurement and Precision
NOTES
You need your clicker
(from the 1st Day)
Equipment Scavenger Hunt
Answers on my CP Chem
page (on my website!)
Accuracy vs. Precision
• Accuracy is how close your measurement
is to the actual or accepted value.
• Precision is the degree of “exactness” of a
set of measurements – something you can
repeat the same way again and again. Also,
a number with more significant figures is
more precise than one with less.
• accurate
(the average is accurate)
not precise
• precise
not accurate
• accurate
and
precise
The Basic Rules of Sig. Figs!
1. NONzero Numbers are ALWAYS significant!
(ex. (123456789!)
2. ZEROs within other nonzero numbers ARE sig.
(ex. 50005  all are significant!)
3. Zeros that are PLACE HOLDERS are NOT
significant! (.0000005 or 50000)
*However a decimal shows precision (50000.)
We will use the DOT RIGHT, NOT LEFT method.
• When using or averaging a set of numbers, the final answer can
only be as precise as THE LEAST precise number!!!!!
• Look for the number that is the least precise and round the
answer to the same number of digits.
• For addition and subtraction: Line up the numbers and round
to the last decimal place of the least precise number.
• Add the following set and round the answer to the correct
number of places.
.0029, 1.00988, 15.2, 12.098
• For multiplication and division: Round the final answer to the
same NUMBER of SIGNIFICANT FIGURES as the number of sig.
fig.s in the least precise measurement.
Example: .05x2001 = 100 (only 1 S.F.)
What is the most commonly
used SI unit/units for the
following?
Mass – g (kg for physics)
Length – m
Volume – L (usually ml for chem)
Density – g/ml or g/cc
How to Convert????
The easy way: 1. Write down the scale or use the print out of the entire scale.
Kilo- hecta- deka- X
K
Try
h
da
deci-
base unit
centid
c
1g  µg
2. Find out what unit you have.
(grams)
3. Count the # of spaces you need to move.
4. Figure out what direction to go.
millim
microµ
(3 dec. places)
The metric system is based on
multiples of 100.
1. True
2. False
0%
ue
Tr
0%
F
se
al
Response Grid
What is 5.0121 rounded to the
hundredths place?
0%
0%
Response Grid
es
e
th
of
No
ne
0%
5
0%
5.
5.01
5.0
5
None of these
5.
01
a.
b.
c.
d.
What is 5.0121 rounded to the
tenths place?
5.01
5.0
5
None of these
0%
0%
Response Grid
No
ne
of
th
es
e
5
0%
5.
0%
5.
01
a.
b.
c.
d.
What is 152,251 rounded to the
hundreds place?
152
152,000
152,250
152,300
Response Grid
0%
15
23
00
0%
15
22
50
0%
15
20
00
0%
15
2
a.
b.
c.
d.
What is 152,251 rounded to the
thousands place?
152
152,000
152,250
152,300
Response Grid
0%
15
23
00
0%
15
22
50
0%
15
20
00
0%
15
2
a.
b.
c.
d.
How many milliliters are there in
a Liter?
1
10
100
1000
Response Grid
0%
10
00
0%
10
0
0%
10
0%
1
a.
b.
c.
d.
The measurement 20.00 grams is more
precise than 20 grams.
1. True
2. False
Response Grid
se
0%
Fa
l
Tr
ue
0%
Which of the following best describes the
length of the beetle's body in the picture?
1 to 2cm
1.5 to 1.6cm
1.54 to 1.56cm
1.546 to 1.547cm
0%
1.
54
6
to
1.
56
cm
to
to
1.
5
1.
54
2c
m
o
0%
Response Grid
1.
54
7.
..
0%
1.
6c
m
0%
1t
a.
b.
c.
d.
If the black lines in the picture at left just touch
the rim of the penny, which of the following
best describes the penny's diameter?
1 to 2
1.9 to 2.0cm
1.92 to 1.94cm
1.935 to 1.945 cm
0%
1.
94
5.
..
Response Grid
to
1.
93
5
to
1.
92
1.
9
to
1.
94
cm
2
o
0%
.. .
0%
2.
0c
m
0%
1t
a.
b.
c.
d.
What can you estimate from the
left ruler?
1-2 in
1.5 in
1.45 in
1.450in
Response Grid
n
0%
1.
45
0i
in
0%
1.
45
in
0%
1.
5
in
0%
12
a.
b.
c.
d.
What can you estimate from the
RIGHT ruler?
1-2 in
1.5 in
1.45 in
1.450in
Response Grid
n
0%
1.
45
0i
in
0%
1.
45
in
0%
1.
5
in
0%
12
a.
b.
c.
d.
Levi collects the following measurements:
50.33g, 50.32g, 50.31g
The actual accepted value is 55.60 grams, what
can we say about his data?
at
e.
..
cc
ur
sa
re
c is
e,
It
i
sp
re
c is
e
sp
It
i
0%
...
0%
.. .
0%
It
i
a. It is precise and
accurate.
b. It is precise, but not
accurate.
c. It is accurate, but not
precise.
Katie collects the following measurements:
55.63g, 55.62g, 55.61g
The actual accepted value is 55.60 grams, what
can we say about her data?
at
e.
..
cc
ur
sa
re
c is
e,
It
i
sp
re
c is
e
sp
It
i
0%
...
0%
.. .
0%
It
i
a. It is precise and
accurate.
b. It is precise, but not
accurate.
c. It is accurate, but not
precise.
These two are equivalent: .230km in 230m
and equal in number of significant digits.
1. True
2. False
0%
ue
Tr
0%
Fa
e
ls
Which number has 4 significant
figures?
1.00
1020
100.
1000.
B and D
0%
B
an
d
D
0%
10
00
.
0%
10
0.
0%
10
20
0%
1.
a.
b.
c.
d.
e.
Bob is going to run 5km. This is
the same as running 5000m.
1. True
2. False
se
0%
Fa
l
Tr
ue
0%
Which number has the most
significant figures?
0%
0%
..
e.
lh
av
al
Th
ey
0%
10
00
0%
10
0
10
100
1000
They all have the
same # of sig. figs
10
a.
b.
c.
d.
How many tablespoons are in a
cup?
10
12
14
16
0%
16
0%
14
0%
12
0%
10
a.
b.
c.
d.
There are 4 pecks in a bushel.
1. True
2. False
se
0%
Fa
l
Tr
ue
0%