General Science Grade 8 Student Textbook PDF

General Science GRADE 8 Student TextBook UNIT ONE BASICS OF SCIENTIFIC INVESTIGATION Learning Outcomes: At the end of this unit, You will be able to: identify the basic and derived units of measurements; explain the concept of...

General Science GRADE 8 Student TextBook UNIT ONE BASICS OF SCIENTIFIC INVESTIGATION Learning Outcomes: At the end of this unit, You will be able to: identify the basic and derived units of measurements; explain the concept of measuring physical quantities; describe the components of a scientific investigation; demonstrate ability to work effectively and respectfully with others in performing fair testing. Main contents 1.1 Scientific Measurments 1.2 Doing Scientific Investigation 1 General Science GRADE 8 Student TextBook Introduction This unit contains two sub units: scientific measurement and do- ing scientific investigation. Under scientific measurement the in- digenous and modern methods of measurement, the classification of physical quantities into fundamental and derived quantity and the difference between accuracy and precision will be discussed. Under doing scientific investigation, the importance, procedures and ethical issues of a scientific investigation will be discussed. Finally using locally available materials, a simple investigation will be conducted. 1.1 Scientific Measurements At the end of this section, you will be able to: explain the concept of measuring physical quantities; describe the various indigenous methods of measurement; distinguish between the basic and derived physical quantities; categorize the basic and derived units of measurements (length, mass, time, temperature, volume, area, density, force); identify prefixes and perform conversions among units of measurements; distinguish between accuracy and precision in measurements. Introduction Making observation is common experience in science. Similarly, it is usual asking the basic questions like how big an object is? How tall are you? To answer these questions, measurements have to be made. Measurement is the process of obtaining the magnitude of a quantity relative to an agreed standard. 2 General Science GRADE 8 Student TextBook In this section both the indigenous and modern methods of measurement will be discussed. The indigenous method of measurement refers to a measurement practiced locally while the modern method refers to a measurement applied by the scientific community. Indigenous Methods of Measurements An indigenous method of measurement refers to measurement methods that are practiced locally for a long period of time and are passed from generations to generation. In this section, we will pay attention to the measurement of length, mass, and time. A. Length Length is a measure of the distance between two points. In Ethiopia we use different indigenous units of length measurement. The commonly used ones are: 1. Hand-span: The hand-span is the measure from the tip of your little finger to the tip of your thumb when your hand is stretched out, Fig 1.1 (a). 2.Digit: A digit is the width of an adult human male fingertip, Fig 1.1 (b). 3.Cubit: A measure of distance from the tip of one’s elbow to the tip of the middle finger when your arm is extended, Fig 1.1 (c). 4.Foot: A measure of distance from the back of the heel to the tip of the big toe, Fig 1.1 (d). 5.Pace: A linear distance measure of a person’s extended walk. A pace is a unit of length consisting either of one normal walking step. The pace is the distance measured from the heel of one foot to the heel of the same foot when it next touched the ground, Fig 1.1 (e). 6. Arm span: Arm span also known as fathom is the distance from the middle fingertip of the left hand to that of the right hand when you stretch your arms out as far as they can reach, Fig 1.1 (f). 3 General Science GRADE 8 Student TextBook Figure 1.1 Indigenous Length measurements Figure 1.1 Indigenous Measurement Length Activity 1.1: Make a group containing 5 students. Using your hand Activity 1.1: Make a group containing 5 students. Using your hand span, span,cubit cubit and digit digit measure measurethe thewidth widthof of a table a table or aor a desk desk in your in your classroom.Record classroom. Recordyour yourmeasurement measurement in in the the table table below. below. No Name of the student Measurement result making measurement 1 2 3 4 Question: Did each of you obtain the same measure for that bench? Question: Did each of you obtain the same measure for that table or Justify desk? the difference Justify of students‘ the difference measurement. of students’ measurement. 11 hand-span, digit, cubit, foot, pace Exercise 1.1: Compare the size of your and arm-span and write them in order of increasing value. B. Mass The amount of matter present in a substance is called mass. Like length, there is also an indigenous method of measuring mass. The following are some examples of the indigenous unit of mass measurement used in Ethiopia. 4 General Science GRADE 8 Student TextBook 1. Weqet- Weqet is a mass measuring unit usually used to measure the mass of powder of gold in local markets. 2. Quntal – Quntal (may be taken from the English word quintal) is a bag used to measure the mass of grains. It is equal to a hundred kilogram. 3. Feresula:- is used to measure the mass of pepper and coffee. It is equal to 17 kilogram. Figure 1.2 Indigenous mass measurements Exercise 1.2: Discuss about the reliability of the above three indigenous mass measuring methods. C. Time Time is the measure of the duration for an interval.There is also an indigenous method of measuring time. Our elders were used the shadow of a tree to measure time. As the position of the Sun changes from morning to evening the length of the shadow of a tree varies. In the morning and late in the afternoon, the length of the shadow is high. At noon when the Sun is overhead no shadow will be seen. Using this fact they could tell the approximate time of the day by just looking at the position of the shadow of a tree found at or near their home. Activity 1.2: Using a long tree found in your school, mark the time at different height of the shadow of the tree. Use this shadow clock for some time. Discuss your observation. 5