Perfect Guide. Lower Secondary SCIENCE. Notes. Book A. Christopher N. Prescott

Transcription

1 Perfect Guide Lower Secondary SCIENCE Notes Book A Christopher N. Prescott

2 x x x x Preface PERFECT GUIDE TO LOWER SECONDARY SCIENCE NOTES is a study aid for school examinations. With comprehensive notes, this study guide promises to build knowledge and facilitate understanding for effective learning. These books can be used in conjunction with the Lower Secondary Science Matters (2nd Edition) textbooks. Textbook links are provided for convenient referencing and further reading. Features in these books IMPORTANT TERMS AND POINTS are highlighted in bold. These terms are also found in the Glossary. Concise STUDY NOTES with ample illustrations and photographs. 5 TOPIC APPLICATION OF FORCES 5.1 STUDY NOTES (a) Describe forces as pushing or pulling actions and show an understanding of how we can detect such forces. A force is a pushing or pulling action. The following actions involve pushing and pulling: stretch squeeze twist press fold/bend lift We cannot see forces but we can see the effect of a force on an object: Causes a stationary object to move. Makes a moving object move faster. Changes the direction of a moving object. Slows down or stops a moving object. Changes the shape and size of an object. Common Error Force is a type of energy as it causes When forces move, energy is used up as work is done. motion. However, force is not a type of energy. PHYSICS Each LEARNING OUTCOME is followed by study notes. COMMON ERROR Refutes common misconceptions. EXAM TIP Useful hints for exams. (b) Show an understanding of how you can measure forces and state its S.I. unit. The S.I. unit of force is the newton (N), named after the English scientist Isaac Newton. This is equivalent to the pull of gravity on an apple of mass 100 g. 6 Theory: You can repeat the experiment with different volumes of water and find that the results were always the same. If you had enough results, you could plot a graph as shown below. The theory you have confirmed is: The rate of evaporation of a liquid depends on the surface area of the liquid and not its volume. Volume of water evaporated (cm 3 ) Surface area (cm 2 ) of water in the container Inferences and hypotheses are the same. Exam Tip 1.2 WORKED EXAMPLES 1. A good scientist will have the following science skills: 2013 Marshall Cavendish International (Singapore) Private Limited Topic 5 Forces and Pressure 57 Common Error Inferences always come after experimentation whereas hypotheses always come before experimentation. In experiments, be able to identify the control variables (variables you keep constant to ensure fair test). Also distinguish the independent variable (variable you change) from the dependent variable (variable you measure). observing inferring communicating planning Match each of the following science activities to one of the above skills. (a) Drawing graphs. (e) Making models. (b) Taking photographs. (f) Looking for patterns. (c) Making hypotheses. (g) Recording volumes. (d) Smelling grapes. (h) Collecting data in a computer. Answer Analysis Exam Tip (a) Communicating: Graphs can show overall patterns in results and are a good way of displaying large amounts of data. (b) Observing: Photographs give a permanent record of a result. They can also be used to slow down (stroboscopic photography) or speed up (time-lapse photography) the recording of results. (c) Planning: A hypothesis is a prediction. After experimentation, this hypothesis is either confirmed or rejected. If it is confirmed, it becomes a scientific theory Marshall Cavendish International (Singapore) Private Limited Topic 1 Introducing Science 13 Liquid pressure like air pressure acts equally in all directions. It does not depend on the shape of the container. It does depend on the density of the liquid and it increases with depth. Link Lower Secondary Science Matters Volume B (2 nd Edition) Section GLOSSARY OF TERMS Atmospheric pressure The pressure caused by the gravitational attraction of the air to Earth. Force A pushing or pulling action. Size of force is measured in newtons (N). Forcemeter An instrument to measure forces. Most of these normally have springs inside. Friction The force produced when one material rubs against another. It is a force which always opposes motion. It will slow a moving object down and eventually cause it to stop. Fulcrum The turning point or pivot when using a lever. Gravitational force The force of attraction between an object and the earth. (gravity) Isobar A line on weather map joining places with the same atmospheric pressure. Lever A simple machine used to move or lift heavy weights. Lubricant A liquid which reduces friction between surfaces (oil or grease). Magnetic force An attractive or repulsive force between materials like iron. Millibar The unit of measurement of atmospheric pressure (1mB = 100 Pascal). Moment (forces) The turning effect of that force about a pivot or fulcrum (unit is Nm). Neap tide acting A small tide caused by the Moon and Sun s gravitational force at right angles to one another. Newton The S.I. unit of force and weight (N). Parallax error The error caused by reading the scale of an instrument at an angle. You should always read the scale of an instrument when looking vertically at it Marshall Cavendish International (Singapore) Private Limited Topic 5 Forces and Pressure 69 PHYSICS TEXTBOOK LINK For further reading GLOSSARY OF TERMS at the end of every chapter provides explanations to various scientific terms Marshall Cavendish International (Singapore) Private Limited Topic 1 Introducing Science iii

3 Contents Topic 1 : Introducing Science 1 PHYSICS Topic 2 : Physical Properties of Matter 15 Topic 3 : Ray Model of Light 32 Topic 4 : Electrical Systems 42 Topic 5 : Application of Forces 57 Topic 6 : Energy and Work Done 71 Topic 7 : Sound Energy 81 Topic 8 : Heat Energy 90 iv Topic 1 Introducing Science 2008 Marshall Cavendish International (Singapore) Private Limited

4 TOPIC 1 INTRODUCING SCIENCE 1.1 STUDY NOTES (a) Describe science as the systematic study of the world around us and technology as the application of scientific knowledge for practical purposes. Science is the systematic study of the natural and physical world through observation, experimentation and analysis. Science is not confined to the laboratory and shows itself in all aspects of our lives. It is important to have a healthy curiosity about the natural and physical world around you. Three main areas of science are Physics, Chemistry and Biology. Science Physics is the study of matter and energy including light, sound, electricity, magnetism, radiation and motion. Chemistry is the study of molecular structures of matter and their interactions. Biology is the study of living things from the tiniest microscopic organisms to the largest whales. Science can give meaningful explanations of why things happen and help to predict what might happen in the future. Science helps to create machines and inventions which improve our surroundings and the quality of life. We call the use of scientific knowledge for practical purposes technology. Examples are found in areas like communication (information technology), transportation, medicine and computers. (b) State some benefits and abuses of science and technology. Show an appreciation of Science as a human endeavour which has been contributed to by different civilisations over the centuries. Recognise that science and technology cannot solve all of society s problems Marshall Cavendish International (Singapore) Private Limited Topic 1 Introducing Science 1

5 Benefits of science and technology Abuses of science and technology Science can solve some of society s problems such as diseases (by developing drugs and medicines) and shortage of food (by using fertilisers and pesticides). However, science cannot solve all of society s problems. Sometimes, science itself creates problems, such as drug abuse, pollution and global warming. (c) State the various safety rules in a science laboratory and recognise the various hazard symbols used in the laboratory. A science laboratory should be a safe place for conducting experiments. To ensure that it is a place safe to work in, the following safety rules should be observed. Safety Rules 1. Do not enter a laboratory or carry out any experiments without supervision from your teacher. 2. Do not run around in a laboratory. Leave coats and school bags outside the laboratory. 3. Do not eat or drink in the laboratory. 4. Read all instructions carefully before carrying out any experiment. 5. Handle all equipment and materials carefully. Never touch or taste chemicals. 6. Always wear safety goggles when heating or mixing chemicals. 7. Report all accidents, breakages or spillages immediately. 8. Try to keep your workbench clean and dry. Dispose of all chemicals in waste bins, not down the sink. 9. Never remove any chemicals or apparatus from the laboratory. 10. When in doubt whether something is safe or not, ask your teacher. Many chemicals used in the laboratory can be dangerous. These substances have hazard symbols on the labels of their containers. The important hazard symbols are: Symbol Hazard Explosive substance This may react violently when heated or struck. It must be handled carefully. Example: Flash powder Flammable substance This catches fire easily. It must be kept away from naked flames. Examples: Petrol, alcohol, kerosene Toxic substance This is poisonous. Always wash your hands after handling it. Examples: Methanol, cyanide, mercury, chlorine Continued 2 Topic 1 Introducing Science 2013 Marshall Cavendish International (Singapore) Private Limited

6 Symbol Hazard Irritable substance This can irritate the skin. It can produce vapours that irritate the eyes, nose and throat. When handling it, always use a spatula. Examples: Phenol, chloroform Corrosive substance This eats away some materials. You must quickly wash with tap water if such substance is spilled. Example: Sulphuric acid Radioactive substance This gives off harmful radiation. It must be stored in lead-lined containers. Example: Uranium Common Error Inflammable substances do not catch alight. Inflammable substances catch alight easily. It is best to describe such substances as flammable. flammable hazard symbol (d) Identify common laboratory equipment and know its use in the laboratory. There are many types of laboratory equipment and apparatus, especially glassware, in your school laboratory. You should know how to use simple apparatus and be able to draw sectional diagrams of such apparatus. The diagrams are in outline and must be in the correct proportions. Apparatus Diagram Use Test tube To contain or heat a small amount of solid or liquid. Beaker To contain, heat or mix chemicals. Funnel To separate an insoluble solid from a liquid using filter paper. Continued 2013 Marshall Cavendish International (Singapore) Private Limited Topic 1 Introducing Science 3

7 Apparatus Diagram Use Conical flask To mix liquid chemicals such as acids and alkalis. Round-bottomed flask To prepare gases when heating is required. Flat-bottomed flask To prepare gases when heating is not required. Gas jar To collect gases. Water trough Measuring cylinder To hold a large amount of water in a container. To measure a certain volume of liquid. Burette To accurately add a measured volume of liquid. Thistle funnel To pour a liquid into a flask when preparing a gas. Crucible To heat a solid strongly. Continued 4 Topic 1 Introducing Science 2013 Marshall Cavendish International (Singapore) Private Limited