©Praxis Publishing_Focus On Science
©Praxis Publishing_Focus On Science
CONTENTS About This Book iv Science and Measurements 1 1.1 What is Science? 2 1.2 Science Laboratory 7 1.3 Measurements 14 1.4 Measuring Tools 17 Recall 32 Put on your Thinking Cap 33 Project 34 Matter 35 2.1 States of Matter 36 2.2 Physical and Chemical Changes 54 2.3 Density 58 Recall 63 Put on your Thinking Cap 64 Project 65 Temperature and Heat 66 3.1 Temperature and Scale 67 3.2 Thermometers 68 3.3 Expansion and Contraction of Matter 71 3.4 Heat Capacity 79 3.5 Heat Transfer 84 3.6 Heat Conductors and Heat Insulators 89 3.7 How Types of Surfaces Affect Heat Absorption and Emission 92 3.8 Body Temperature Regulation 97 Recall 100 Put on your Thinking Cap 101 Project 102 Motion and Force 103 4.1 Motion 104 4.2 Force and Motion 116 Recall 125 Put on your Thinking Cap 126 Project 127 CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 ii ©Praxis Publishing_Focus On Science
Living Things 128 5.1 Biodiversity 129 5.2 Living and Non-living Things 133 5.3 Classification of Living Things 136 Recall 151 Put on your Thinking Cap 152 Project 153 Interactions Among Organisms and the Environment 154 6.1 Biotic and Abiotic Components 155 6.2 Food Chains and Food Webs 160 6.3 Nutrient Cycles in an Ecosystem 163 6.4 Interactions between Organisms 165 6.5 Factors that Affect the Organisms and Environment 168 Recall 178 Put on your Thinking Cap 179 Project 180 Earth and the Solar System 181 7.1 The Solar System 182 7.2 Earth and Its Satellite 189 7.3 The Sun 197 Recall 200 Put on your Thinking Cap 201 Project 202 CHAPTER 5 CHAPTER 6 CHAPTER 7 iii ©Praxis Publishing_Focus On Science
ABOUT THIS BOOK Focus-on Science is a pedagogy-driven series developed to provide a clear and effective learning trajectory for Grade 7 to Grade 9 students. The inquiry approach used in the Textbook assists students in acquiring scientific knowledge and science process skills through a variety of activities, experiments and projects. To make learning more engaging, photographs, infographics, diagrams and examples are used to present the content. In addition, animations, videos, simulations and Augmented Reality (AR) models are included to help bring science to life. Chapter Opener A short write-up with trigger questions based on a photo, as in the chapter introduction, to pique students’ interest. Experiment Engages and helps students to develop science process skills, manipulative skills and an inquisitive attitude through welldesigned laboratory experiences. Sudi fastens his seat belt before he starts to drive. What happens to Sudi when the brake is applied suddenly upon seeing a cat crossing in front his moving car? Why is it necessary to use the seat belt? Motion and Force CHAPTER 4 What will you learn? Describe motion in terms of distance, displacement, speed, velocity and acceleration Measure speed Understand the relation between force and motion Understand Newton’s Laws of Motion and their applications in daily life Demonstrate Newton’s Law of Motion The temperature of a matter increases when it is heated and decreases when it is cooled. However, the temperature remains constant during a change of state, that is during melting (solid to liquid), boiling (liquid to gas), freezing (liquid to solid) and condensation (gas to liquid). During melting and boiling, the kinetic energy gained by the particles is used to overcome the forces of attraction between the particles. The temperature of the solid or liquid remains the same. On the other hand, during condensation and freezing, the particles release energy to the surroundings, thus enabling them to be pulled closer together. The temperature of the liquid or gas remains the same. Temperature (°C) Boiling point Melting point Ice Water Ice + Water Steam Time (min) Water + C Steam B D A Problem statement Does temperature remain constant during the changes of state? A Temperature during the melting of ice Hypothesis The temperature of ice remains constant during the melting process. Manipulated variable Responding variable Constant variable Quantity of ice cubes Materials and apparatus glass rod and wire gauze Ice cubes, thermometer, beaker, Bunsen burner, tripod stand, Procedure 1 Set up the apparatus as shown in the diagram below. Ice cube Thermometer Glass rod Wire gauze Bunsen burner 2 Experiment Temperature remains constant during changes of state At point A to B, the temperature of the mix of ice and water remains the same, at the melting point. At point C to D, the temperature of the mix of water and steam remains the same, at the boiling point. The change of temperature during the heating of ice 48 What will you learn? The chapter’s learning outcomes which provide an idea of what students will learn. iv ©Praxis Publishing_Focus On Science
Science Facts Provides additional information related to the topic taught in order to stimulate students’ interest in learning science. Activity Provides students with a total learning experience through learning by doing, encouraging them to reflect on the experience and think critically. The blue whale is the world’s largest animal, reaching a length of 30 metres or more and weighs as much as 24 elephants. Some species of whales can live for more than 200 years. Science Facts What is the best tool for measuring the circumference of an infant’s head? Why? Think About It Measuring Length Length is the distance between two points. The SI unit for length is metre (m). Short lengths are measured in centimetres (cm) or millimetres (mm). Long distances are measured in kilometres (km). A ruler such as the metre rule can be used to measure the length of short straight lines or objects. The metre rule gives an accuracy of 0.1 cm. The correct reading is obtained only when the eyes are vertically above the mark on the ruler. Parallax error happens when the measurement reading is more or less than the actual reading. This occurs when the mark on the ruler is viewed from the wrong position. 0 1 2 3 cm 4 5 6 7 8 9 10 11 12 13 14 15 Correct One end of the object is at the ‘0’ mark. Wrong Wrong 18 The correct eye position when taking a reading Activity 2 Aim: To measure average and instantaneous speed of a toy car on the runway Materials and apparatus: Photogate (timing gate) system and electronic timer, toy car and runway Procedure: A Measuring average speed 1 Set up the apparatus as shown in the diagram. Distance between two timing gates Black strip to break infrared beam Transparent card First timing gate linked to the timer Second timing gate linked Toy car to the timer Runway Electronic timer 15 cm 2 Adjust the distance between two timing gates to 50 cm. 3 Release the toy car from the high end of the runway. 4 Catch the toy car once it passes the second timing gate. Record the time taken. B Measuring instantaneous speed 1 Set up the apparatus as shown. Transparent card Length of black strip that breaks the infrared beam Timing gate linked to the timer Toy car Runway Electronic timer 15 cm 2 Release the toy car from the high end of the runway. 3 Catch the toy car once it passes the timing gate. 4 Record the time taken. Results: Activity A Calculate the average speed of the toy car in m/s by dividing the distance between the timing gates by the time taken. Activity B Calculate the instantaneous speed of the toy car in m/s by dividing the length of the black strip by the time taken. Discussion: Why is it advisable not to place the timing gate too high on the runway or too close to the bottom of the runway? Measuring speed Caution • Do not place the timing gates too high on the runway. • Do not place the timing gates too close to the bottom of the runway. After a hot shower, it is likely that Chapter 4 Motion and Force 109 you would not be able to see your reflection in the mirror. You have to wipe off the moisture from the mirror’s surface first. This is because condensation occurs when warm water vapour comes into contact with the cooler mirror surface. Have you ever wondered why we can see someone’s breath when he is out in very cold weather? Water exists on Earth in all three states of matter: solid, liquid and gas. Liquid water can be found in the oceans, rivers, lakes and streams, as well as in the soil and underground. Glaciers and snow all contain solid ice. The Earth’s atmosphere contains water vapour which is a gas. Let’s study how water exists in different states in the water cycle. When the warm and moist vapour of his breath comes into contact with the cold and humid air, it condenses into tiny water droplets. We can see these droplets take on a cloud-like appearance. Water cycle Resource 53 Chapter 2 Matter Think About It Provides questions that encourage students to find the answers to support constructivist learning. Resource Helps students make learning more enjoyable and in a more engaging way via scanning QR codes to access fascinating videos, animations, simulations, AR models, etc. Resource v ©Praxis Publishing_Focus On Science
THINKING CAP Put on your 1 Have you noticed that an electric fan continues to revolve for some time even after the current is switched off? How do you explain this? 2 How does swimming relate to Newton’s Third Law of Motion? Explain. 3 Why does a bird flap its wings shortly before it takes-off? 126 1 The systematic study of nature and how it affects us and our environment is known as . The application of scientific knowledge for the use of mankind is called . 2 We use to carry out experiments and make accurate measurements or observations in the laboratory. 3 Students must follow rules and precautions in the laboratory in order to prevent accidents when they carry out the experiments. 4 Students must be able to recognise the hazard warning that are placed on labels of bottles or containers of hazardous substances in order to handle the substances properly. 5 A investigation is a series of steps done systematically to study a problem or an event that involves the use of one or more science process skills. 6 The process of utilising numbers to define physical quantities is known as . 7 A quantity is a quantity that can be measured and has value. 8 Length, mass, time, temperature and electric current are quantities. 9 Area, volume, density and velocity are obtained by multiplying or dividing two or more basic quantities. They are known as quantities. 10 Unit is the process of converting one unit of measurement to another for the same quantity by multiplying or dividing by conversion factors. 11 Length is the distance between two points and its SI unit is . 12 Micrometer screw gauges are used to measure the and diameters of small objects while vernier calipers are used to measure short lengths, the internal and external , and the of objects. 13 An area is the extent of a surface or a plane figure. The SI unit for area is . 14 The of a liquid can be measured using a measuring cylinder, beaker, pipette or burette. 15 The volume of regular-shaped and irregular-shaped solids can be measured by using the water method. 16 The of an object is the quantity of matter contained in the object while the of an object is the pull of the Earth on the object. 17 A is the standard instrument used to measure time intervals in the laboratory. The SI unit of time is . 18 The measurement of how hot or cold an object is its . Its SI unit is and it is measured using a . 19 The density of a substance is defined as its mass per unit volume and its SI unit is . RECALL Fill in the missing words. 32 Project Activity objective: Introduce Newton’s First Law of Motion Problem statement: Newton’s first law of motion states that an object remains at its original state, whether it is at rest or moving at uniform velocity in a straight line, unless acted upon by an external force. Also known as the law of inertia, it has important applications in our daily life and this project will demonstrate the first part of the law: An object at rest stays at rest. Concept applied: Newton’s First Law of Motion Procedure: 1 Work in a group of five students. Each group is to build a tower of at least 60 cm tall. 2 Brainstorm the design of the tower and the role of each member in the group. 3 Determine the material to build the tower. The material used must be stackable and it is a set of identical material. For different testing, materials of different mass will be used to build the towers. 4 Build the tower. 5 Prepare notecards by punching a hole on one end and tying a string through the hole. Place the cards in the tower as shown in the picture. 6 Starting at the top, pull the first notecard quickly from the tower. Observe and record your result. 7 Continue to pull one or two more cards from top to bottom and observe what happens. 8 What improvements need to be done if the test is not successful? 9 If this was done successfully, get everyone in the group to pull the cards out at the same time. Would the result be the same as in steps 6 and 7? 10 What improvements need to be done if the test is not successful in step 9? 11 Now try to build a tower of the same height by using materials that has less mass. 12 Repeat steps 6 to 10 and record your result. 13 Alternatively, you can try another test where the cards are without the holes and string. Would this make the pull easier? Would this affect the result? Presentation: You may present your findings with a video or any method that is suitable. Share with the groups the improvements you had done for successful testing. Submit a report. Inertia Tower Chapter 4 Motion and Force 127 Put on your Thinking Cap Challenges students with questions that promote higher-order thinking skills. Recall Assists students in recalling concepts learned and serves as a summary of key points. Project Appears at the end of each chapter that helps students develop problem-solving and critical thinking skills, and to connect what students have learned to the real world. vi ©Praxis Publishing_Focus On Science
How do you tell if you have a fever? Do you check your forehead with your hand? What tool do you need to take a body temperature reading? What type of measurement do you use when you take the reading using the proper tool? Science and Measurements CHAPTER 1 What will you learn? Explain what science is and its importance Plan a safe and fair test, and carry out the test via a scientific investigation Name the base quantities and their SI units Understand that derived quantities are formed from base quantities Know how to use prefixes and do the conversion of units Measure length, area, volume, mass, time, temperature and density using the proper tools ©Praxis Publishing_Focus On Science
1.1 What is Science? Have you ever wondered why you land on the ground again after jumping in the air? This natural occurrence shows that gravity pulling you towards the centre of the Earth. Science is the systematic study of nature and how it affects us and our environment. The information produced from the study of science is known as scientific knowledge. Using scientific knowledge, we invent useful devices and the application of scientific knowledge for the use of mankind is called technology. We use technology in almost every aspect of life, thus making science part of our everyday life. How science benefits us in various fields Medical—More diseases can now be treated with the discoveries of new drugs, vaccines, antibiotics and the invention of better surgery techniques and equipment. Communication—Global communication is now possible with the use of communication satellites, e-mail, the lnternet, telephones and mobile phones. In homes—Facilities such as electricity and tap water make life easier and more comfortable. Various appliances help us to do our housework easier and faster. Transportation—Science and technology have made it possible to manufacture automobiles, aeroplanes, ships and boats, among other things, making it easier to transport people and goods. Agriculture—Machines are used to carry out heavy and difficult tasks such as ploughing and harvesting. How does science benefit us? 2 ©Praxis Publishing_Focus On Science
Artificial Intelligence (AI) Climate change is the greatest threat to the planet. It will require every possible solution, including technology such as artificial intelligence (AI). Researchers collaborate to find a solution to climate change using machine learning. Machine learning is the science of designing and implementing algorithms that can learn from previous cases. If something happened in the past, we can predict what will happen in the future. Technology utilisation frequently allows us to create new scientific discoveries and inventions. We can process massive amounts of data for research thanks to ICT and smart computers. We now use artificial intelligence on a daily basis, whether it be in speech recognition software or navigational apps. In actuality, it affects the majority of us in our daily lives. In 2020, the world experienced the Covid-19 pandemic. Most countries started taking action such as shutting down schools to stop the coronavirus from spreading. Due to school closures, students are unable to attend classes. As a result, we shifted the classroom to online learning. How has AI aided in the resolution of numerous issues over this time period? Via online teaching, students can learn from home using computers, laptops or mobile phones. Your device can serve as your virtual teacher. They allow you to learn at your own pace by providing a variety of online teaching and learning activities, such as quizzes, animations and simulations. When you need to conduct research for a school assignment, search engines will explore the entire Internet and offer the results you need with the help of AI. These results are tailored for you, powered by AI and based on your search history. Chapter 1 Science and Measurements 3 ©Praxis Publishing_Focus On Science
Tools like spellcheckers are used to ensure that your emails are error-free before sending them to your teachers. AI and natural language processing are used in these tools. Spam filters are used by recipients to identify emails that they would like to receive in their inbox or to prevent emails that are identified as spam. Machine learning is also used by antivirus software to protect your email account. When you unlock your phone via biometrics, such as face ID, AI is used to enable that functionality. It compares the scan of your face with the information it has stored about your face to determine if the person trying to unlock your phone is really you. When you need to order food using your smartphone, simply speak the command and it will suggest the nearest location to get your favourite food. You can pay online using an app, and the food will be delivered to your door. Can you elaborate on other applications of AI in daily life? 4 ©Praxis Publishing_Focus On Science
Fields and Careers in Science Science is divided into various fields. Each field involves different, specialised studies. Here are some examples of these studies. Field What is the field about? Examples Biology Study of living things Zoology, botany, microbiology, physiology Physics Study of matter and energy and how they interact with each other Engineering, electricity Chemistry Study of matter and its reactions Pharmacology, toxicology, forensics Geology Study of rocks, soils and minerals Geochemistry, geophysics, geomorphology Astronomy Study of the Moon, stars, planets, the Sun and other objects in space Astrophysics Meteorology Study of weather and climate change Hydrometeorology Fields of science and examples With the wide range of fields in science, you can choose various careers based on your interest. For example, if you want to be an engineer, you need to be proficient in physics; if you want to be a doctor, you need to be proficient in biology. However, do you still need to learn physics and chemistry to be a doctor? Careers in science Biology Physics Chemistry Geology • Engineer • Astronomer • Meteorologist • Architect • Pharmacist • Chemist • Biochemist • Forensic scientist • Geologist • Environmentalis • Geophysicist • Geochemist • Zoologist • Medical doctor • Botanist • Geneticist Chapter 1 Science and Measurements 5 ©Praxis Publishing_Focus On Science
Activity 1 Scientists are experts who study or work in a scientific field. They have given their knowledge, experience and time to help change the world. The photographs below show some of the scientists who have made significant contributions in various fields of science. Scientists and their contributions 1 Name the scientists above. One of the examples has been done for you. You may use the Internet or other sources to help you. 2 Some of their contributions are listed below. Match. (a) He played a key role in the development of calculus and created the first practical reflecting telescope through his extensive study of light. However, the most important and famous of his discoveries was that of gravity, which is one of the most significant contributions to the world of physics. (b) He discovered penicillin, which became the world’s first antibiotic and revolutionised modern medicine. (c) He is best known as one of the inventors of the telephon, but he also had a deep understanding of sound science and made significant contributions to the detection of hearing loss. (d) He was the first to propose a cosmology theory based on a combination of general theory of relativity and quantum mechanics. 3 Name other scientists and state their contributions. A D B C 6 ©Praxis Publishing_Focus On Science
1.2 Science Laboratory The place where a scientist works is called a laboratory. Students carry out scientific investigations or experiments during science lessons in science laboratories. Different types of apparatus are used in the laboratory to carry out experiments. The following shows some common laboratory apparatus in three-dimensional and twodimensional diagrams as well as their uses. For containing, collecting and transferring chemicals A test tube is used for containing small amounts of chemicals or for mixing solutions. A boiling tube is a scaled-up test tube with a larger size. It is made from glass that can withstand high temperatures as it is used for heating small amounts of chemicals. A beaker is used for containing, mixing and heating large amounts of chemicals and liquids. A conical flask is used for collecting filtrates. A round-bottomed flask is used for containing chemicals when uniform heating is required. A flat-bottomed flask is used for mixing solutions when no heating is required. A gas jar is used for collecting gas. A bell jar is used for enclosing samples and separating samples from the surroundings. For measuring the volume of liquids 0 10 20 30 40 50 60 70 80 90 100 ml A measuring cylinder is used to measure the volume of a liquid. A burette is used to measure the volume of a liquid accurately. 100 100 A pipette is used for measuring and transferring a fixed volume of liquid. For filtering and evaporating A filter funnel is used for separating insoluble solids from mixtures. An evaporating dish is used for evaporating excess solvents to produce concentrated solutions. Chapter 1 Science and Measurements 7 ©Praxis Publishing_Focus On Science
For heating A Bunsen burner is used to supply a flame for heating. Wire gauze Tripod stand A wire gauze is used to allow even distribution of heat. A crucible is used for heating solids to extremely high temperatures. A test tube holder is used for holding a test tube when it is hot. A tripod stand is used for supporting apparatus during heating. For holding and supporting apparatus Retort stand Clamp Retort stand and clamp are used for holding apparatus during experiments. A test tube rack is used for holding test tubes in a vertical position. Uses of some common laboratory apparatus There are rules and safety precautions that must be followed by students in order to prevent accidents. Listed below are some rules and safety precautions in the laboratory. What you should do Always follow the teacher’s instructions. Read the label on a reagent bottle before using its content. Turn off the Bunsen burner after use. Wash and return all apparatus to their proper place after use. Report any breakages to the teacher. Keep the bench clean and tidy. Wash your hands before leaving the laboratory. What you should not do Never enter the laboratory unless a teacher is present. Do not eat, drink or taste any chemicals. Never touch chemicals with your bare hands. Use a spatula. Do not pour back any unused chemicals into its bottle. Do not throw solid wastes into the sink. Do not run or play in the laboratory. Do not test anything without the teacher’s permission. Wire gauze Tripod stand 8 ©Praxis Publishing_Focus On Science
Some substances in the laboratory are hazardous or dangerous. Hazard warning symbols are placed on the labels of bottles or containers of hazardous substances to show the danger of the substances. As young scientists, you must be able to recognise the symbols and know how to handle the substances properly and prevent accidents. Symbol Danger of substances Examples Handling techniques Explosive • Easily explodes when mixed with other substances. • Sodium, potassium • Keep in paraffin. • Avoid contact with water. • Concentrated acids and alkalis • Keep away from other substances including water. Flammable or inflammable • Easily catches fire and can cause burns. • Organic solvents such as ethanol, petrol and kerosene • Keep away from fire or heat sources. Toxic / poisonous • Causes death or harm to the body if absorbed through the skin, swallowed or inhaled. • Mercury, chloroform, lead, benzene, bromine, sodium cyanide, hydrogen sulphide • Do not inhale, touch or taste the substances. • Keep in a locked cupboard. Corrosive • Causes damage to the skin or eyes upon contact. • Concentrated acids and alkalis, bromine, hydrogen peroxide • Avoid contact with skin or eyes. • Spills on body parts should be washed away quickly under running water. Irritant / harmful • Irritates (causes itchiness and rashes) skin, eyes and respiratory system. • Ammonia solution, chloroform, dilute acids and alkalis • Spills on body parts should be washed with a lot of water Radioactive • Gives out radiation that can cause cancer or destroy bodily tissues. • Uranium, plutonium, radium • Keep in special lead containers. Hazard warning symbols Chapter 1 Science and Measurements 9 ©Praxis Publishing_Focus On Science
Scientific Investigation We obtain scientific knowledge by carrying out scientific investigations. A scientific investigation is a series of steps done systematically to study a problem or an event. Each step involves the use of one or more science process skills. These refer to the twelve types of skills, which are needed for scientific investigations. Positive attitudes towards science such as staying curious, persevering, not giving up, keeping an open mind, being fair, objective and honest, are important in the study of science. Identifying the problem • Determine what we want to find out. • To do so, we need to gather information by observing things and happenings. Based on observations, we ask why and how something happens. Planning an experiment • Determine the materials and apparatus required. • Determine the procedure to carry out the experiment and methods of collecting and analysing data. Carrying out the experiment Section involved: • Control the variables as planned so that the experiment is a fair test. • Collect data through observations and measurements. All these must be done systematically, accurately, objectively and honestly. Analysing and interpreting data • Explain the collected data in an objective and logical manner. • Give an explanation about the pattern or relationship between the variables based on the data collected. Experimenting Planning and conducting an investigation to test a hypothesis, collecting data, interpreting data until a conclusion is made. Making a conclusion • State whether the hypothesis is true. • Make a conclusion based on the data and not on a biased opinion. Writing a report on the experiment • Present the aim, materials, apparatus, procedures, results, table or graph, and conclusion clearly in the report. • It is important as a means of communication among scientists. Science process skills involved in a scientific investigation and a sample science report • Think of as many ideas to explain the observations or why and how something happens. • Identify the variables involved and their relationships. A variable is anything that can be controlled, manipulated (independent variable) or measured (dependent variable) in an experiment. • Formulate a hypothesis which has to be tested based on the evidence collected. Forming a hypothesis 10 ©Praxis Publishing_Focus On Science
Making an inference Making an initial explanation of an observation. Making a hypothesis Making a general statement about the relationship between the manipulated variable and the responding variable to explain an event or observation. This statement can be tested to determine its validity. Observing Using the five senses to gather information on a subject or phenomenon. Classifying From observations, grouping things or phenomena based on their similar characteristics. Measuring and using numbers Making quantitative observations using numbers or tools with standard units. Predicting Forecasting events based on observations or previous experience or from existing data. Defining operationally Defining concepts by describing what is observed. Using space-time relationship Describing changes in parameters such as location, direction, shape, size, volume, weight and mass, with time. Interpreting data Giving rational explanations based on collected data. Communicating Presenting information or ideas in writing, verbally, tables, graphs or models. Controlling variables Identifying manipulated (independent) variables, responding (dependent) variables and constant (controlled) variables. In an investigation, a variable is manipulated to observe its relationship with the responding variable. At the same time, the other variables are kept constant. I think different materials have different heat conductivity. The diameter and length of these rods must be the same. With this microscope, I can see what an animal cell looks like... We can interpret the data and present it in the form of graph. Chapter 1 Science and Measurements 11 ©Praxis Publishing_Focus On Science
A complete report, which is an important means of communication among scientists should be written based on the findings in the experiment. An example of the report is as shown below. Problem How does the length of the pendulum affect the period of oscillation? Hypothesis The longer the length of the pendulum, the longer the period of oscillation. Manipulated variable Length of the pendulum Responding variable Period of oscillation Constant variable Weight of the pendulum Materials and apparatus String, cork, wooden block, retort stand with clamp, stopwatch and metre rule Procedure 1 A simple pendulum of 20 cm in length is made as shown in the figure. P Q Wooden block Retort stand String Length of pendulum = 20 cm 2 The time taken for the pendulum to make 20 oscillations is recorded. 3 The experiment is repeated using the pendulum with lengths of 40 cm, 60 cm, 80 cm and 100 cm. 4 The results are recorded in a table and a graph of the time taken to complete one oscillation against the length of the pendulum is plotted. Result Lenght of pendulum (cm) 20 40 60 80 100 Time taken for 20 oscillations (s) 16 25 31 36 40 Time taken for one oscillation (s) 0.8 1.3 1.6 1.8 2.0 Length of pendulum (cm) 20 40 60 80 100 2.0 1.5 1.0 0.5 0 Time taken to complete one oscillation (s) Conclusion The longer the length of the pendulum, the longer the period of oscillation. The hypothesis is accepted. 12 ©Praxis Publishing_Focus On Science
Scientific Attitudes and Values in Carrying Out Scientific Investigations When conducting scientific investigations, you should have the attitudes and values listed in the checklist below. How many do you think you have? When conducting scientific investigations, we should put our best ethical and moral principles into practice. When attempting to understand how the world works, scientists also used these methods. They express their curiosity by posing queries, coming up with plans for repeating trials, gathering information and finding the answers to those queries. They keep doing the same thing until they find the answers because they are persistent and consistent in doing so. 4 Realise that science is a means to understand nature. 4 Be responsible with the safety of yourself, others and the environment. 4 Appreciate and practise clean and healthy living. 4 ✓ Diligent and persistent in carrying out a task. 4 Thankful to God. 4 Interested and curious about the environment. 4 Cooperative. 4 Virtuous. 4 Flexible and open-minded. 4 Systematic, confident and ethical. 4 Appreciate the contributions of science and technology. 4 Honest and accurate in recording and validating data. 4 Willingness to tolerate uncertainty. Chapter 1 Science and Measurements 13 ©Praxis Publishing_Focus On Science
Based on the photos given, what do we measure? Think About It Physical Quantities Physical quantities are quantities that can be measured and have values.They are divided into base quantities and derived quantities. Physical quantities are measured in SI units. SI units are the abbreviation of the French term ‘Le Systéme International d’Unités’ which means International System of Units. Before the SI units were introduced, there was no uniformity in units of measurement, thus causing difficulties and confusion in communicating data. Since the use of SI units as the standard units all over the world, this has resolved many problems that stem from this miscommunication. 14 1.3 Measurements Measurement can be defined as the process of utilising numbers to define physical objects. The sentence, “This boy is taller than that boy” serves no comparing purpose. But if the first boy’s height is 170 cm and the second boy’s height is 160 cm, the first boy is 10 cm taller than the second boy. Mathematically, this sentence makes greater sense. In science, we often make quantitative observations using measuring instruments to get accurate results. The result of the measurement is a numeric value with certain units. We make measurements in our daily lives What units are shown on the packaging of these products? ©Praxis Publishing_Focus On Science
Base Quantities Base quantities are independent physical quantities that have single standard units. The examples are length, mass, time, temperature and electric current. They can be measured with instruments. The following table gives the base quantities, their SI units and the instruments used for measuring. Base quantity (symbol) SI unit (symbol) Measuring instrument Length (l) metre (m) Metre rule Mass (m) kilogram (kg) Lever/beam balance Time (t) second (s) Stopwatch Temperature (T) Kelvin (K) Thermometer Electric current (I) Ampere (A) Ammeter Derived Quantities Derived quantities are the results of the combination of basic quantities. Derived quantities such as area, volume, density and velocity are obtained by multiplying or dividing two or more basic quantities. Derived quantity (symbol) Formula and example units involved Symbol for unit Area (A) length (m) × width (m) m2 Volume (V) length (m) × width (m) × height (m) m3 Density (ρ) mass (kg) ÷ volume (m3 ) kg m–3 Velocity (v) distance (m) ÷ time (s) m s–1 By adding a prefix to a SI unit, we can use it to simplify the description of a physical quantity that is very big or very small. Giga, mega and kilo are used for big quantities. Deci, centi, milli, micro and nano are used for small quantities. Prefix Symbol Numerical value Standard form Giga G 1 000 000 000 × 109 Mega M 1 000 000 × 106 Kilo k 1000 × 103 Deci d 0.1 × 10–1 Centi c 0.01 × 10–2 Milli m 0.001 × 10–3 Micro μ 0.000 001 × 10–6 Nano n 0.000 000 001 × 10–9 Chapter 1 Science and Measurements 15 ©Praxis Publishing_Focus On Science
Activity 2 1 Measure (a) the length of an exercise book with your hands and a ruler (b) the weight of a beaker using a traditional beam balance and an electronic balance (c) the time taken to complete a walk of 10 steps using an hourglass and an electronic stopwatch 2 Write down the measurements of using these methods. 3 Which method is better for measuring? 4 Explain why the method you stated in no. 3 is important for measuring. Using non-standard and standard techniques to measure Conversion of Units Unit conversion is the process of converting one unit of measurement to another for the same physical quantity. This is done by multiplying or dividing the measurement by conversion factors. When the bigger units are converted to smaller units, multiplication method is used. Conversely, when the smaller units are converted to bigger units, the division method is used. The conversion of units table is given below: Physical quantity How to convert Example Length × 1000 × 100 × 10 ÷ 1000 ÷ 100 ÷ 10 km m cm mm 3 km = 3 × 1000 = 3000 m = 3 × 100 000 = 300 000 cm 3000 cm = 3000 ÷ 100 = 30 m = 3000 ÷ 100 000 = 0.03 km Mass × 1000 × 1000 ÷ 1000 ÷ 1000 kg g mg 5 kg = 5 × 1000 = 5000 g = 5 × 1 000 000 = 5 000 000 mg 50 000 mg = 50 000 ÷ 1000 = 50 g = 50 000 ÷ 1 000 000 = 0.05 kg Area × 1 000 000 × 10 000 × 100 ÷ 1 000 000 ÷ 10 000 ÷ 100 km2 m2 cm2 mm2 7 m2 = 7 × 10 000 = 70 000 cm2 = 7 × 1 000 000 = 7 000 000 mm2 70 000 cm2 = 70 000 ÷ 10 000 = 7 m2 = 70 000 ÷ 10 000 000 000 = 0.000007 km2 16 ©Praxis Publishing_Focus On Science
1.4 Measuring Tools Rulers are used to determine the length of a straight line between two points. Do we measure the distance we go between locations with rulers? We should use the most appropriate measuring tools in the correct way to get the most accurate and consistent reading. Let’s explore the three important aspects in measurement. Accuracy 4 Accuracy is how close a measured value is to the actual value of a physical quantity. 4 A measured value with a small or no error is said to be more accurate. 4 The error in a measurement is the difference between the measured value and actual value. Sensitivity 4 The ability of an instrument to detect small changes in the quantity that is being measured. 4 Measuring instruments that have smaller scale divisions are more sensitive. For example, a milliammeter is more sensitive than an ammeter. Consistency 4 The ability of an instrument in measuring a quantity in a consistent manner. 4 Measurements are said to be consistent when the values of the measurement are close to each other when a measurement is done repeatedly. Assume the actual value is at the midpoint. It is considered more accurate if the arrow lands in the red circle. When the arrow lands in the orange circle, it is deemed less accurate. Accurate and consistent. Not accurate and not consistent. Chapter 1 Science and Measurements 17 ©Praxis Publishing_Focus On Science
The blue whale is the world’s largest animal, reaching a length of 30 metres or more and weighs as much as 24 elephants. Some species of whales can live for more than 200 years. Science Facts What is the best tool for measuring the circumference of an infant’s head? Why? Think About It Measuring Length Length is the distance between two points. The SI unit for length is metre (m). Short lengths are measured in centimetres (cm) or millimetres (mm). Long distances are measured in kilometres (km). A ruler such as the metre rule can be used to measure the length of short straight lines or objects. The metre rule gives an accuracy of 0.1 cm. The correct reading is obtained only when the eyes are vertically above the mark on the ruler. Parallax error happens when the measurement reading is more or less than the actual reading. This occurs when the mark on the ruler is viewed from the wrong position. 0 1 2 3 cm 4 5 6 7 8 9 10 11 12 13 14 15 Correct One end of the object is at the ‘0’ mark. Wrong Wrong 18 The correct eye position when taking a reading ©Praxis Publishing_Focus On Science
Vernier Calipers Vernier calipers are used for a variety of exact measurements, such as to measure the thickness of an object, the internal and external diameters of circular objects, and the depth of objects. There are the main scale and the vernier scale on the vernier calipers. The main scale has the smallest division of 0.1 cm while the vernier scale has the smallest division of 0.01 cm. The diagram shows the correct way of using a pair of vernier calipers. Zero error is the error that occurs when the measuring instrument does not show zero before taking the measurement. Thus to ensure the reading is accurate, always close the jaws of the vernier calipers without any object in between and check for the zero error before using it. Inside jaws are used to measure the internal diameter Outside jaws are used to measure the external diameter Tail is used to measure the depth Vernier scale Main scale 0 cm 1 2 3 4 5 6 7 8 9 10 0 5 10 2 cm 3 0 5 10 Main scale Iron pipe Vernier scale No zero error means the ‘0’ mark of both the main scale and vernier scale is perfectly aligned 0 0 10 1 Main scale Vernier scale Calipers and micrometer screw gauges are commonly recognised as essential and common tools in most machining shops. Using a set of digital equivalents of these equipment, the measurement is shown rapidly and precisely on an electronic screen. Science Facts 4 The external diameter of the iron pipe = main scale + vernier scale reading reading = 2.1 cm + 0.07 cm = 2.17 cm 1 Grip the iron pipe to be measured between the outside jaws. 2 Read the main scale where it lines up with the ‘0’ mark of the vernier scale. The reading of the main scale is 2.1 cm. 3 Read the first mark on the vernier scale that aligns perfectly with any line on the main scale. The reading of the vernier scale is 0.07 cm. Chapter 1 Science and Measurements 19 ©Praxis Publishing_Focus On Science
Micrometer Screw Gauge A micrometer screw gauge is used to measure the thickness and diameters of small objects, such as paper and wire. It has two scales which are the main scale and the vernier scale. The vernier scale has 50 equal parts and its smallest division is 0.01 mm. Thus, it gives a more accurate reading compared to that of vernier calipers. The steps below show the correct way of using a micrometer screw gauge. 0 mm 5 10 5 0 45 0 mm 5 10 5 0 45 Datum line Main scale Vernier scale Rope Spindle Anvil Ratchet Thimble 1 Place the rope to be measured between the anvil and spindle, then rotate the thimble to grip it gently. Then, rotate the ratchet until a ‘click’ sound is heard. 2 Read the main scale. The reading is 6.5 mm. 3 Read the mark on the vernier scale that aligns perfectly with the datum line on the main scale. The reading is 0.02 mm. 4 The thickness of the rope = main scale reading + vernier scale reading = 6.5 mm + 0.02 mm = 6.52 mm To ensure the accurate reading, always check for the zero error before using the tool. Make sure the gap between the anvil and the spindle is closed. Measuring Area An area is the extent of a surface or a plane figure. The SI unit for area is square metre (m2 ). Square kilometre (km2 ) can be used as a unit for large areas. Other units for smaller areas are square centimetre (cm2 ) and square millimetre (mm2 ). The area of objects with regular shapes such as a rectangle, a triangle or a circle can be calculated using mathematical formulae. To measure the area of an irregular shape, an estimation is normally done as shown in (a) to (c). 20 ©Praxis Publishing_Focus On Science
(a) First, the shape of the object (e.g. leaf) is traced on the graph paper. (b) Then, every square that is fully covered, half-covered and more than half-covered is ticked. (c) The total number of ticks in this case is counted as 9. This gives the estimated area in cm2 = 9 × 1 cm2 = 9 cm2 . 1 cm 1 cm Measuring Volume A volume is the amount of space occupied by a three-dimensional object. The SI unit for volume is cubic metre (m3). Other units of volume are cubic centimetre (cm3) and cubic millimetre (mm3 ). The volume of solids is usually measured in cm3 and m3 units whereas the volume of liquids is measured in millilitre (ml) and litre (l). The relation between the units of volume: 1 cm3 = 1 ml 1 l = 1000 ml = 1000 cm3 1 m3 = 1 000 000 cm3 = 1 000 000 ml Measuring the Volume of Liquids The volume of a liquid can be measured using a measuring cylinder or a beaker. However, a more accurate measurement can be made using either a burette or a pipette. The level of the liquid in any measuring tool is curved. This curve is known as the meniscus. 30 20 40 Meniscus Wrong reading: 28 ml Correct reading: 27 ml Wrong reading: 26 ml The correct eye position when taking a reading Chapter 1 Science and Measurements 21 ©Praxis Publishing_Focus On Science
To avoid errors when taking a reading, ensure that the eye position is at the same level as the bottom of the meniscus of the liquid. This must be done for all liquids except mercury. The meniscus of water is concave while the meniscus of mercury is convex. Take the reading at the bottom of the meniscus Take the reading at the top of the meniscus Liquids Mercury The menisci of liquids and mercury Measuring the Volume of Solids The volume of regular-shaped and irregular-shaped solids can be measured by using the water displacement method. A measuring cylinder with a known volume of water is used. There is a new volume reading when the object is immersed. The volume of the object is determined by the difference between the two readings. Activity 3 1 First, fill half of a measuring cylinder with water. Record the initial volume of the water. 2 Lower a solid object slowly into the measuring cylinder. Record the final volume. 3 Find the difference between the two readings to obtain the volume of the solid object. Initial volume Water Final volume Thread Stone 4 What is the method used in this activity? 5 How to measure the volume of a solid such as a cork that is less dense than water? 6 Name one other tool that is used to measure the volume of regular-shaped and irregular-shaped solids. Measuring the volumes of solids Archimedes established that the volume of water displaced by an object when it is submerged is equal to the volume of the object itself in an experiment to ascertain if a crown was composed of pure gold or not. By comparing the crown to a known density of gold, Archimedes was able to determine its true composition. Science Facts 22 ©Praxis Publishing_Focus On Science
Measuring Mass The mass of an object is the quantity of matter contained in the object. The mass of an object is the same everywhere. This is because the quantity of matter in an object is the same wherever the object is. The mass of an object is measured using a lever balance, a beam balance or an electronic balance. The SI unit for mass is the kilogram (kg). There is a difference between mass and weight. The weight of an object is the gravitational pull of the Earth on the object. Weight depends on the gravitational pull (at a place) that acts on the object. As a result of this pull, the weight of an object differs from place to place. The weight of an object is measured using a spring balance or a compression balance. The SI unit for weight is Newton (N). The weight of an object having a mass of 1 kg is 10 N. Balances for measuring mass The 5 cm bee hummingbird, which weighs less than 2.0 g, is the smallest extant hummingbird species while the 23 cm enormous hummingbird is the largest hummingbird species, measuring 18–24 g. The mass of an apple is about 100 g. The mass of an orange is about 50 g. The mass of a kiwi fruit is about 45 g. Can you estimate the mass of other fruits in this photo? A beam balance Scale Scale Indicator A beam balance AA lever balance Scale Scale Indicator A beam balance A lever balance Chapter 1 Science and Measurements 23 ©Praxis Publishing_Focus On Science
Activity 4 Aim: To estimate length, area and mass of objects Materials and apparatus: Pencil, ruler, paper clips, leaf, graph paper with 1 cm 3 1 cm grid, A4 paper (100 pieces) and balance Procedure: A Length 1 Estimate the length of a paper clip. 2 Arrange the paper clips next to a pencil as shown in the diagram below. 3 Calculate the number of paper clips required to become the same length as the pencil. Then, estimate the length of the pencil and record the result in the table. 4 Measure the length of the pencil using a ruler and record the reading in the table. B Area 1 Place a leaf on a graph paper. Trace the outline of the leaf using a pencil. 2 Tick (3) for all the complete squares, half squares and more-than-half squares. (Area of each square = 1 cm2 ) 3 Estimate the area of the leaf. C Mass 1 Weigh 100 pieces of A4 paper on a balance. 2 Repeat step 1 three times to obtain an average reading. 3 Estimate the mass of one piece of A4 paper. Result: A Length Estimation length of the pencil (cm) Actual length of the pencil (cm) B Area Area of leaf = ___________ cm2 C Mass Mass of 100 pieces of A4 paper (g) Mass of one piece of 1 2 3 Average A4 paper (g) Determining estimated measurements 24 ©Praxis Publishing_Focus On Science
Minute Second Discussion: 1 What is the definition of length? 2 Is the estimated length of the pencil the same as the actual length of the pencil in Activity A? 3 What is the definition of area? 4 What is the formula used to calculate the area of a rectangular object? 5 Is the area of the leaf determined in Activity B accurate? 6 If the grid of the graph paper is changed to 1 2 cm 3 1 2 cm, what would happen to the estimated area? 7 What is the definition of mass? 8 Using 50 pieces of A4 paper and 500 pieces of A4 paper, which is a better way to determine a more accurate estimation of mass for an A4 paper in Activity C? Conclusion: Write down your conclusion. Measuring Time The SI unit of time is second (s). Seconds are used to quantify shorter time intervals while minutes, days, months and years are used to quantify longer time intervals. A stopwatch is the standard instrument used to measure time intervals in the laboratory. It has two scales: the external scale indicates the time in seconds and the internal scale indicates the time in minutes. Did you know how to use the stopwatch? • Press the button twice in rapid succession to clear the previous reading and reset to zero. • Press and release the button once to start recording the time. • Press the button one more time to stop the stopwatch. • The readings on the minute scale and second scale are taken. What is the time recorded as shown in this stopwatch? Start, stop and reset button Chapter 1 Science and Measurements 25 ©Praxis Publishing_Focus On Science
Our body temperature is measured using a clinical thermometer that has a temperature range of 35°C to 42°C. Measuring Density Density of a substance is defined as its mass per unit volume. It is stated mathematically as: = m V where m is the mass of a substance in kg and V is the volume in m3 . Thus, the SI unit for density is kg m-3. Did you know that a hydrometer is an instrument used to measure a liquid’s density? A multi-layered drink with colourful layers that uses the concept of density looks appealing and impresses customers. Why do helium-filled balloons float in the air? Think About It What is the correct way to read a thermometer? Think About It Measuring Temperature We come across hot and cold objects in our daily lives. However, we cannot always rely on our sense of touch to determine how hot or cold an object is. The concept of temperature was introduced in order to measure exactly how hot or cold an object is. Its SI unit is kelvin (K). However, temperature is commonly measured in degrees Celsius (°C) or in degrees Fahrenheit (°F) in daily use. A laboratory thermometer has a temperature range of –10°C to 110°C, with a 1°C precision. 26 ©Praxis Publishing_Focus On Science
Measuring is an important skill in scientific investigations. We say that a measurement is accurate if it is very close to the actual value. Inaccurate measurements may lead a scientist to make a wrong conclusion to an experiment. Measurements cannot be 100% accurate all the time. However, we can increase the accuracy of measurements by (a) using suitable measuring tools. For example, to measure 1 ml of water, we should use a burette instead of a measuring cylinder. The scale of a burette is smaller. (b) using the right techniques. For example, employing the correct eye position when taking a reading. (c) taking several readings. Then, the average of the readings is determined and taken as the measurement. Activity 5 Aim: To study the correct methods to use measuring tools Materials and apparatus: Pencil, ruler, mineral water bottle, measuring tape, tap water, dry cells, thermometer, stopwatch, ammeter, voltmeter and measuring cylinder Procedure: 1 Carry out the activities in the table below. 2 Repeat step 1 three times for each activity. 3 Record the measurement readings in the same table. Result: Activity Measuring tool Measurement Reading 1 2 3 Average 1 Ruler Length of a pencil 2 Measuring tape Circumference of mineral water bottle 3 Thermometer Temperature of tap water 4 Stopwatch Time taken by a student to jump 10 times in one place 5 Ammeter Electric current supplied by two dry cells in a closed circuit 6 Voltmeter Voltage supplied by two dry cells in a closed circuit 7 Measuring cylinder Volume of tap water Correct methods to use measuring tools Chapter 1 Science and Measurements 27 ©Praxis Publishing_Focus On Science
Discussion: 1 Why do each measurement need to be repeated three times? 2 Tick (3) on the correct eye position when taking the following readings. Then, state the reading value. (a) (c) (b) (d) 3 What is the proper way to use a stopwatch? Arrange the steps in the correct order. Press and release the button once to start recording the time. Take the readings on the minute scale and second scale. Press the button twice quickly to reset the reading to zero. Press the button again to stop the stopwatch. 4 In general, what are the two types of error that you might make while using a measuring tool? Conclusion: 1 Readings should be taken times to obtain more accurate data. 2 Students’ eye position should be above the mark on the ruler, measuring tape, stopwatch, ammeter and voltmeter. 3 For the measuring cylinder and thermometer, the eye position should be at the same level as the of the liquids. 0 cm 1 2 3 4 5 6 7 9080 30 20 Mercury 28 ©Praxis Publishing_Focus On Science
Activity 6 Aim: To compare the accuracy of measuring tools Materials and apparatus: Beaker, copper wire, textbook, vernier calipers, digital vernier calipers, micrometer screw gauge, digital micrometer screw gauge, digital thermometer, clinical thermometer, triple beam balance and digital balance Procedure: 1 Measure the internal and external diameters of a beaker using a pair of vernier calipers as shown in Diagram (a). 0 cm 1 2 3 4 5 6 5 100 10 Vernier scale Main scale Beaker Beaker Inside jaw Outside jaw (a) 2 Repeat step 1 three times to obtain an average reading. 3 Repeat steps 1 and 2 using a pair of digital vernier calipers. 4 Measure the diameter of a copper wire using a micrometer screw gauge as shown in Diagram (b). (b) 5 Repeat step 4 three times to obtain an average reading. 6 Repeat steps 4 and 5 using a digital micrometer screw gauge. 7 Hold the bulb of the clinical thermometer in one hand for 2 minutes as in Diagram (c). Read and record the temperature reading. (c) Comparing Accuracy in Measurements Vernier scale Main scale Copper wire 0 5 20 15 10 5 0 –10 10 20 30 40 50 60 70 80 90 100 110 Clinical thermometer Chapter 1 Science and Measurements 29 ©Praxis Publishing_Focus On Science
8 Repeat step 7 three times to obtain an average reading. 9 Repeat steps 7 and 8 using a digital thermometer. 10 Weigh a textbook on a triple beam balance as in Diagram (d). (d) 11 Repeat step 10 three times to obtain an average reading. 12 Repeat steps 10 and 11 using a digital balance. Result: Measuring tool Reading 1 2 3 Average (a) Vernier calipers Internal diameter External diameter (b) Digital vernier calipers Internal diameter External diameter (c) Micrometer screw gauge (d) Digital micrometer screw gauge (e) Clinical thermometer (f) Digital thermometer (g) Triple beam balance (h) Digital balance 30 ©Praxis Publishing_Focus On Science
Discussion: Write down the accuracy of each of the measuring tools. Measuring tool Accuracy (a) Vernier calipers (b) Digital vernier calipers (c) Micrometer screw gauge (d) Digital micrometer screw gauge (e) Clinical thermometer (f) Digital thermometer (g) Triple beam balance (h) Digital balance Conclusion: Digital vernier calipers, digital micrometer screw gauge, digital thermometer and digital balance are more _____________ measuring tools. Chapter 1 Science and Measurements 31 ©Praxis Publishing_Focus On Science
1 The systematic study of nature and how it affects us and our environment is known as . The application of scientific knowledge for the use of mankind is called . 2 We use to carry out experiments and make accurate measurements or observations in the laboratory. 3 Students must follow rules and precautions in the laboratory in order to prevent accidents when they carry out the experiments. 4 Students must be able to recognise the hazard warning that are placed on labels of bottles or containers of hazardous substances in order to handle the substances properly. 5 A investigation is a series of steps done systematically to study a problem or an event that involves the use of one or more science process skills. 6 The process of utilising numbers to define physical quantities is known as . 7 A quantity is a quantity that can be measured and has value. 8 Length, mass, time, temperature and electric current are quantities. 9 Area, volume, density and velocity are obtained by multiplying or dividing two or more basic quantities. They are known as quantities. 10 Unit is the process of converting one unit of measurement to another for the same quantity by multiplying or dividing by conversion factors. 11 Length is the distance between two points and its SI unit is . 12 Micrometer screw gauges are used to measure the and diameters of small objects while vernier calipers are used to measure short lengths, the internal and external , and the of objects. 13 An area is the extent of a surface or a plane figure. The SI unit for area is . 14 The of a liquid can be measured using a measuring cylinder, beaker, pipette or burette. 15 The volume of regular-shaped and irregular-shaped solids can be measured by using the water method. 16 The of an object is the quantity of matter contained in the object while the of an object is the pull of the Earth on the object. 17 A is the standard instrument used to measure time intervals in the laboratory. The SI unit of time is . 18 The measurement of how hot or cold an object is its . Its SI unit is and it is measured using a . 19 The density of a substance is defined as its mass per unit volume and its SI unit is . RECALL Fill in the missing words. 32 ©Praxis Publishing_Focus On Science
THINKING CAP Put on your 1 Explain why you should not pour any unused chemicals back into its bottle. 2 Assume that 2.54 cm is equivalent to 1 inch. How many inches are there in a metre? 3 The following describes the properties of objects. Every object has a mass and a volume. The mass of an object remains the same in all places, unlike its weight. (a) Based on the statements given above, what is the difference between mass and weight? (b) Does the mass of an astronaut change when he lands on the Moon? Give your reasons. Chapter 1 Science and Measurements 33 ©Praxis Publishing_Focus On Science
Project Activity objective: Explore research method and techniques used by scientists in order to develop hypotheses, conduct experiments, collect and analyse data, and draw conclusions to communicate the results. Concept applied: Scientific investigation Procedure: 1 Carry out this project individually at home. 2 Examine the materials you have at home. Choose one material and start asking some questions about the material. Identify one question and carry out a scientific investigation to find an answer to the question. 3 Include the following in the planning of the investigation. (a) The aim of the investigation (b) Problem statement (c) Tools and materials (d) Hypothesis (e) Variables (f) Procedure (can apply diagrams if needed) (g) Result/Observation (h) Conclusion Reflection: 1 What have you learned from the investigation you carried out? 2 Do you need to improve any of the procedure in order to get an accurate result/ observation? If yes, what are they? 3 What are the new skills or knowledge that you have achieved through the investigation you constructed? 4 If the investigation is carried out in pairs or groups, what are the values you have learned? 5 What scientific attitudes did you practise when conducting the investigation? Presentation: Write a complete report of the investigation based on the standard format that you have learned. Include your answers of the reflection section. Scientific Investigations 34 ©Praxis Publishing_Focus On Science
We are used to seeing steam coming from a hot drink. In the picture on the right, is the steam coming from the hot coffee, or from the air above it condensing due to heat from the coffee? If the hot coffee is replaced with hot chocolate, how do you turn the hot chocolate, liquid form to solid form? Matter CHAPTER 2 What will you learn? Describe the arrangement and movement of particles in solid, liquid and gas, and their properties Explain what happens in changes of state using the particle theory Describe the physical and chemical changes Define density and calculate the density of a material Explain why some objects float and some objects sink in water ©Praxis Publishing_Focus On Science
Solid Solid 2.1 States of Matter Matter is anything that has mass and volume. According to the particle theory of matter, matter is made up of very small particles that cannot be seen with a light microscope. These tiny particles are discrete. This means that the particles are completely separate from one another and there are spaces between them. The particles of matter are in constant motion. Solid The particles in a solid are packed closely together in a fixed and regular pattern. They are held together in fixed positions by very strong forces of attraction. The spaces between particles are very small. Thus, they cannot move around and can only vibrate in their fixed position. With an increase in temperature, the particles gain kinetic energy and vibrate faster and more strongly. Solids cannot be compressed because the particles are close together and have very little space to move into. Thus, they have a fixed shape and volume. As a result, solids do not flow. Due to the limited spaces among the particles, solids diffuse the slowest compared to liquids and gases. In general, solids have the highest density because the particles are closely packed and have a large number of particles per unit volume. Particles of copper Copper Wire Solid, Liquid and Gas Matter can exist in three states which depend on how the particles are arranged. The three states of matter are solid, liquid and gas. Water is an example of a matter that exists in all three states. (a) Water is liquid at room temperature. (b) Ice is water in solid state. (c) Steam and water vapour are water in gaseous state. The arrangement and movement of particles are different in different physical states of matter. Hence, each state of matter has different physical properties. 36 ©Praxis Publishing_Focus On Science
Liquid The particles in a liquid are quite close together but are arranged randomly without a fixed pattern. They are held together by strong forces of attraction but not as strong as in solids. The spaces between particles are moderate. Thus, they are able to move freely and collide with one another. When a liquid is heated, its particles gain kinetic energy, resulting in an increased collision rate. Liquids cannot be compressed to any extent because the particles are still arranged quite closely and have little space to move into. Thus, they have a fixed volume. Since the particles can move, liquid can flow and take the shape of its container. They have moderate density because the particles are arranged randomly without a fixed pattern and has slightly smaller number of particles per unit volume compared to solids. They diffuse slowly. For example, when a perfume is sprayed at a corner in a room, the smell of the perfume can be detected a few metres away. Gas The particles of gas are far apart from one another. They have little or no forces of attraction between them. The spaces between particles are large. Thus, they are able to move freely and randomly in all directions at high speeds. When a gas is heated, collisions occur more frequently among the particles as they gain more kinetic energy and move faster in all directions. Gases can be easily compressed because the particles are far apart and have large spaces to move into. Thus, they have no fixed volume. They flow much more easily than a liquid because the particles move randomly in all directions and spread out as far as they can, occupying the entire space of the container quickly. They take the shape of their container. Gases have very low density because the particles are arranged far apart and has a smaller number of particles per unit volume compared to solids and liquids. They diffuse rapidly. For example, bromine gas in a gas jar diffuses and spreads evenly throughout another gas jar filled with air within a few minutes. Liquid Gas Chapter 2 Matter 37 ©Praxis Publishing_Focus On Science
Activity 1 Aim: To show that matters have mass and occupy space Materials and apparatus: Balloons, needle, thread, cellophane tape, metre rule, green beans, retort stand and clamp, measuring cylinder and lever balance Procedure: Activity A 1 Set up the apparatus as shown below. Balloons Needle Cellophane tape Metre rule P Q Thread 2 Balance two balloons on a metre rule. 3 Use a needle to prick balloon Q through the cellophane tape. Then, record your observation. Activity B 1 Weigh an empty measuring cylinder with a lever balance and record its mass. Lever balance Empty measuring cylinder 2 Place a random amount of green beans into the measuring cylinder. Weigh the measuring cylinder and record its mass. Lever balance Measuring cylinder containing green beans Matter has mass and occupies space 38 ©Praxis Publishing_Focus On Science
Observations: Activity A The air in balloon Q escapes and the metre rule tilts to the . Activity B (a) Mass of empty measuring cylinder = g (b) Mass of measuring cylinder and green beans = g Discussion: 1 What is meant by matter? 2 Give inferences for your observation in (a) activity A (b) activity B 3 Give four examples of objects around you that have mass and occupy space. 4 Rizal found that his flat bicycle tyre inflates after being pumped. Why does this happen? 5 Which of the following substances are matter? (a) Water (b) Sound (c) Soil (d) Time (e) Heat (f) Sunlight 6 Why is the mass of air not measured using the lever balance? Conclusion: Write down your conclusion. Chapter 2 Matter 39 ©Praxis Publishing_Focus On Science
Activity 2 Aim: To make a simulation about the arrangement and movement of particles in solid, liquid and gas Materials and apparatus: A plastic container with partitions, and marbles Procedure: 1 Put marbles in each of the sections A, B and C in the plastic container as shown in the diagram below. A B C Marble Plastic container 2 Move the plastic container back and forth repeatedly. 3 Observe the arrangement and movement of the marbles in each section. Observation: Label section A, section B and section C in the tree map below. Draw the arrangement of the particles, and complete the characteristics of each matter (solid, liquid and gas) with the words given. loose solid orderly very loose high moderate low liquid vibrate randomly quickly gas Arrangement and movement of particles in solids, liquids and gases Matter Section A Section B Section C • Compact and • about a fixed position • kinetic energy • and not in order • Move and sometimes collide • kinetic energy • and in disorder • Move at random and often collide • kinetic energy 40 ©Praxis Publishing_Focus On Science
Discussion: 1 (a) What is represented by the marbles? (b) What is matter made up of? 2 The diagrams below show two syringes, one filled with air and another filled with water. Both syringes are pressed down. Air Water (a) Which syringe is easier to be compressed? The syringe filled with air or the syringe with water? (b) Explain why it is easier to compress that syringe. 3 Based on the diagram below, label solid, liquid or gas for (a) to (d). Conclusion: Particles in solid, liquid and gaseous states have different and . d a c b Chapter 2 Matter 41 ©Praxis Publishing_Focus On Science
Diffusion Rate in Three States of Matter When a freshener is sprayed at a corner in a room, the smell of the freshener can be detected a few metres away. The spread of this freshener’s smell is due to the diffusion of freshener particles from a high concentration area (region A) to a low concentration area (other regions). What do you know about diffusion? Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. It can occur in solids, liquids and gases because there are spaces between the particles of solids, liquids and gases. A few factors influence the diffusion process, altering the rate and extent of diffusion. These factors are: • Temperature • The particle’s size • Area of interaction A room freshener will be diffused into the air allowing us to detect the scent. Let’s look at this example. People sitting in the living room may smell the freshly made food in the kitchen. This is due to air diffusion. Chemical compounds from the food reaches us as aroma. Since the escaping compounds travel more quickly when food is hot due to an increase in kinetic energy, we can smell the food from a distance away. In contrast, the kinetic energy of the aroma emitting from cold food is insufficient to go a wide distance, therefore we can only detect it from a close distance. Region A 42 ©Praxis Publishing_Focus On Science
When a tea bag is submerged in hot water, the process of diffusion begins. The highly concentrated tea particles travel through the beg into the lower concentration of particles in the water. This affects the colour of the water. The particles of tea move through the spaces between the particles of water quickly. Thus, the colourless water turns brown. You can find this substance in the laboratory. When you place this crystal in water, the water will turn purple. What is it? What is its medical use? Think About It When we light the incense stick, the smoke diffuses into the air and spreads throughout the room. It spreads because the particles move in all direction at the same time. As a result, its scent quickly spreads throughout its surroundings. Chapter 2 Matter 43 ©Praxis Publishing_Focus On Science