Measurements
1.
2.
3.
4.
Length
Volume
Temperature
Mass
Will learn to use different measuring instrument
Will learn that the smaller the unit increment, the
more accurate your measurement will be
Will learn the difference between measurements that
are accurate and those that are precise
Will learn to record measurements in the correct
number of digits.
Parts of a Measurement
1. The value (numerical portion)
2. The unit (describes what units)
3. The name of substance being measured
EX:
1 teaspoon salt
2 liters of pop
2
Uncertainty in Measurement
Measurements
-are an estimated amount
-a numerical value with attached units that
expresses a physical quantity such as length, mass,
volume, time or temperature
-are only as good as the instrument used to make
the measurement.
3
Uncertainty in Measurement
• All measurements have a certain degree of
uncertainty
• No matter how careful you are
• No matter how carefully you read the measuring
instrument
• No measurement is perfectly accurate
• The quality of our measurements are stated in
terms of accuracy and precision
4
Uncertainty in Measurements
•Accuracy: how closed the measurement is to the
reference value
•Precision: How close repeated measurements are to
each other
5
Accuracy
= of a measurement is how close that
measurement is to the true or “exact” value
EX: Standard weight = 5.00g
4.98g more accurate than 5.12 g
6
Accuracy
• Also subject to the
reliability of the
measuring instrument
• The smaller the
increments of units on
the instrument, the
more accurate
7
Length Measurements
Measuring the length of a
metal rod
• Ruler A has more
uncertainty and gives less
precise measurements.
• Ruler B has less
uncertainty and gives
more precise
measurements.
Metric Rulers for Measuring
Length.
8
Precision
• Precision = making reproducible or repetitive
measurements of the same quantity
• How fine the divisions are
• There will always be some uncertainty
because of the limits in the accuracy of your
instruments
9
Precision versus Accuracy
Precise and
accurate
Imprecise and
inaccurate
Precise but
inaccurate
It is also possible
to have an
accurate
measurement
without being
precise.
10
“Accuracy is telling the truth…..
Precision is telling the same story over and
over again.”
Yiding Wang
yiang@mtu.edu
11
• Strive for measurements that are accurate and
precise
• Measurements you perform will be used in
subsequent calculations
• In scientific measurements all the digits
known w/certainty, plus the one estimated
digit, are known as significant figures or
significant digits.
12
Significant Figures
Significant figures: is defined to be all digits in a
number representing data or results that are known
with certainty plus the first uncertain digit.
5.4 cm
0
1
2
3
4
5
6
7
8
9
10 cm
9
10 cm
5.48 cm
0
1
2
3
4
5
6
7
8
13
Significant figures or
Significant digits
• ANY numbers generated by means of a
measurement (length, volume, time, etc)
should be expressed in the correct number of
significant figures.
• This reflects how close the measured values
are to the true values.
14
Length Measurements
Lab 3
Scientific Measurements
Page 30
Measurements With a Ruler or
Meter Stick – Look at it FIRST! – Where is
“0”
16
Protractor for Measuring Angles
17
Measuring Angles
Units are degrees (º)
18
Angle Measurements
Lab 3
Scientific Measurements
Page 31
Using a Vernier Caliper
http://phoenix.phys.clemson.edu/labs/cupol/vernier
/
•Used to accurately determine the fraction part of the least
count division.
•Length of an object, the outer diameter (OD) of a round or
cylindrical object, the inner diameter (ID) of a pipe, and the
depth of a hole.
20
Parts of a Caliper
21
Main scale
Auxillary
(Venier) Scale
•
•
•
•
The caliper consists of a main scale engraved on a fixed ruler and an auxiliary
caliper scale engraved on a movable jaw
The movable auxiliary scale is free to slide along the length of the fixed ruler.
The main scale is calibrated in centimeters with the smallest division in
millimeters.
The auxiliary scale has 10 divisions that cover the same distance as 9 divisions
on the main scale. Therefore, the length of the auxiliary scale is 9.0 mm.
22
• When the caliper is closed and properly zeroed the
first mark (zero) on the main scale is aligned with the
first mark on the auxiliary scale.
• The last mark on the auxiliary scale will then coincide
with the 9 mm-mark on the main scale.
• This is read 0.00 cm.
23
24
25
• Once the caliper is positioned to make a reading,
make a note of where the first mark on the auxiliary
scale falls on the main scale.
• We see that the object's length is between 1.2 cm
and 1.3 cm because the first auxiliary mark is
between these two values on the main scale.
26
• The last digit (tenths of a millimeter) is found by
noting which line on the auxiliary scale coincides
with a mark on the main scale.
• The last digit is 3 because the third auxiliary mark
lines up with a mark on the main scale. T
• The length of the object is 1.23 cm.
27
Practice Reading the Following
Calipers
28
Measurement with a Caliper
Lab 3
Scientific Measurements
Page 31