Lesson 2:
MEASUREMENTS
Prepared by: Mark C. Alderite, LPT
Objectives:
At the end of the lesson, the learners:
1.
2.
3.
Explain the need for measurements;
Describe how to carry out measurements
of length, mass, and volume; and
Differentiate between precision and
accuracy
01
UNITS of
MEASUREMENTS
What do we mean by:
01
Length
in measuring the height of
a person; distances; the
size of cloths
03
Mass
in measuring the
weight of a person; the
amount of salt or sugar
being bought
02
Volume
in measuring the amount
of a liquid (e.g. soft
drinks)
Time
in measuring the duration of
an event (e.g. to run through
a distance)
04
Temperature
in measuring the body
temperature of a person
or of the atmosphere.
05
SI units
The International System of
Units (SI) is the metric
system used in science,
industry, and medicine.
Units of the SI System
There are seven base
units in the SI system:
Kilogram (kg) – Mass
Second (s) – Time
Kelvin (K) – Temperature
Ampere (A) – Electric Current
Mole (mol) – Amount of
substance
Candela (cd) – Luminous
intensity
Meter (m) – Distance
Joule (J) - Energy
Imperial Systems
(commonly used in US
and UK)
Gallons (gal), pint, ounces - Volume
Feet (ft), Inches (inch), miles (mi) Length
Pounds (lb), Ounces, stone – Mass
Square feet and acres - Area
SI UNIT PREFIXES
Designation of
multiples and
subdivisions of
unit by combining
with the name of
the unit.
02
Accuracy and Precision
in Measurements
Chemistry is an
experimental science. As
such measurements are
important in conducting
experiments, recording
data and observations,
and making conclusions.
What is precision?
Precision refers to how close each
measurement is to one another.
●
●
The precision is good if the individual
measurements are close to the average.
The precision is poor if the measurement
have a wide deviation from the average
value.
What is accuracy?
Accuracy refers to the closeness of the average
value to the actual or true value, or most
probable value.
•
•
Precise measurements are most likely to be
accurate.
Measurements with high precision can be
inaccurate.
Remember that measurements
could have errors.
In scientific research, measurement error is the
difference between an observed value and
the true value of something. It’s also called
observation error or experimental error.
There are two main types of measurement
error:
• Random error (low in precision) is a chance
difference between the observed and true values of
something (e.g., a researcher misreading a weighing
scale records an incorrect measurement).
There are two main types of measurement
error:
• Systematic error (low accuracy) is a consistent or
proportional difference between the observed and
true values of something (e.g., a miscalibrated scale
consistently registers weights as higher than they
actually are).
By recognizing the sources of error,
you can reduce their impacts and
record accurate and precise
measurements. Gone unnoticed,
these errors can lead to research
biases like omitted variable
bias or information bias.
Significant Figures
in Measurements
and Calculations
SIGNIFICANT FIGURES
In chemistry, Significant figures are the digits of value which carry meaning
towards the resolution of the measurement. They are also called significant
figures in chemistry.
Basic Law of Significant Figures
1. All non-zero digits are significant.
2. Zeroes between non-zero digits are significant.
3. A trailing zero or final zero in the decimal portion only
are significant.
Following are the significant figures rules that govern
the determination of significant figures:
1. Those digits which are non-zero are significant.
For example, in 6575 cm there are four significant figures and in
0.543 there are three significant figures.
2. If any zero precedes the non-zero digit then it is not significant.
The preceding zero indicates the location of the decimal point, in
0.005 there is only one and the number 0.00232 has 3 figures.
Following are the significant figures rules that govern
the determination of significant figures:
3. If there is a zero between two non-zero digits then it is also a
significant figure.
For example; 4.5006 has five significant figures
4. Zeroes at the end or on the right side of the number are also
significant.
For example; 0.500 has three significant figures.
5. Counting the number of objects for example 5 bananas and 10
oranges have infinite figures as these are inexact numbers.
Significant Figures Examples
4308 –
2. 40.05 –
3. 470,000 –
4. 4.00 –
5. 0.00500 –
1.
4 significant figures
4 significant figures
2 significant figures
3 significant figures
3 significant figures
Assessment:
How many significant figures are in each measurement?
1.
2.
3.
4.
5.
6.
246.32
107.854
100.3
0.678
1.008
0.00340
7.
8.
9.
10.
11.
12.
14.600
0.0001
700000
350.670
1.0000
320001
Thank
you!
Does anyone have
any questions?
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Mark C. Alderite, LPT
Science Teacher