X-Physics Textbook 2019 PDF

m a t e ri a l y r i g h t e d cop  Physics Class Ten Author Kinley Gyaltshen, M. Ed. Sumitra Subba, M. Sc. m a te r ia l yr ig h t e d cop Published by Kuensel Corporation Limited, Thimphu Copyright © Authors Edition 2015 Reprint 20...

m a t e ri a l y r i g h t e d cop  Physics Class Ten Author Kinley Gyaltshen, M. Ed. Sumitra Subba, M. Sc. m a te r ia l yr ig h t e d cop Published by Kuensel Corporation Limited, Thimphu Copyright © Authors Edition 2015 Reprint 2018 Acknowledgment We would like to thank all individuals for making contributions in the form of suggestions, feedbacks and comments towards the writing of this textbook. Our gratitude and appreciation also goes to the following teachers for their time and space to attend the review works at Gelephu during the winter vacation of 2015. Their feedbacks and comments were very useful in bringing the book to the current shape. Mr.Surjay Lepcha Mr.Wangpo Tenzin Secondary School Curriculum Officer for Science Curriculum Specialist for Science DCRD DCRD Mr.Shankar Lal Dahal Mrs.Sonam Tshomo Principal Physics Teacher Bajothang Higher Secondary School Dechentsemo Central School Mr.Sherub Gyeltshen Mr.Tika Ram Subba Physics Teacher Physics Teacher Ugyen Dorji Higher Secondary School Nangkor Higher Secondary School Mr.Sherab Tenzin Mr.Kailash Pradhan Physics Teacher Physics Teacher Drukgyel Higher Secondary School Kamji Middle Secondary School Our sincere courtesy to all the sources of pictures that are used in this book. Lastly, sincere prayers of gratitude to all our family members for being there and rendering unwavering support during the times of need. All rights reserved. No part of this book may be reproduced in any form without a written permission from the authors and publishers. If there are any objections with regard to the use of picture and photographs in this book, please contact the publishers. ISBN: 978-99936-53-38-7 m a te r ia l yr ig h t e d cop   Preface This textbook is a progressive one from class IX Physics and all efforts are made to make linkages and progressions to scientific concepts learnt in the previous years. The chapter outlines and contents in this textbook are similar to the ones in the class IX textbook. Teaching and learning of science in our country has under gone major changes in recent times. But it is the first time in Bhutan that text books for class IX to XII are adapted to our context. Theories and laws are universal but we strongly believe that experiments and activities to either introduce or consolidate these facts can be done through our own everyday experiences. Therefore, all efforts are made in these textbook to maintain these essence. The selection of our Physics textbook in class IX has really encouraged us to continue our venture in writing this textbook, and we thought that we should not miss out on our attempts to put all out efforts to try our luck in Class X. Our hard work and effort is now paid as this textbook is selected in Class X. The advantage for students is that they shall experience the same style and flavour of writing. Like the previous book, this textbook contains relevant solved examples after topics, topic end questions, competency based questions, and a model question paper at the end. Special efforts are made to introduce the new concepts by relating to the existing knowledge of the learners and suitable activities are in place to either induce or consolidate their learning. In this textbook too, students will have the opportunity to learn all the 21st century skills for learning through active learning strategies and assessment of their learning. All suggestions and constructive feedbacks are welcome and we shall try our best to accommodate them in subsequent editions. -Authors m a te r ia l yr ig h t e d cop  Table of Content Syllabus Strand: Physical processes 1. Forces and Motion (i) Force and acceleration yy State that the centre of gravity of an object is a point where the entire weight of an object appears to act. yy Describe a simple couple as a pair of equal and opposite parallel forces whose lines of action do not coincide, and results in rotation yy Explain the torque of a couple. yy Explain that a system is in equilibrium if there is no resultant force and no resultant moment. yy Explain the principle of moments to solve problems involving forces acting in two dimensions. (ii) Force and non-uniform motion yy Explain that the forces acting on falling objects change with velocity. yy Describe terminal velocity in falling objects. (iii)Pressure F yy State and use the equation for pressure P = A m yy State and apply the equation for density t = V yy Explain Pascal’s law and its application e.g. in hydraulic systems, car brakes, diving, etc. 2. Energy (i) Energy resources and energy transfer yy Describe efficient ways to use energy yy Describe the need for economical and sustainable use of energy resources, and the environmental implications of our current methods for generating energy. m a te r ia l yr ig h t e d iv cop   (ii) Work and conservation of energy yy Apply the principle of the conservation of energy to gravitational potential energy, kinetic energy and work done against resistive forces. yy Calculate the work done by a constant force (to include examples where the force is not in the same direction as the displacement) using W=Fd(adjacent side/opposite side). yy State and use the equation for potential energy PE=mgh. 1 yy State and use the equation for kinetic energy K.E. = 2 mv 2. W yy Calculate the power of a machine using P = t yy Calculate the efficiency of a machine in P = Wout Win 3. Electricity and magnetism (i) Circuits yy Describe that the flow of charges through a resistor results in heating of resistor. yy Describe the qualitative effect of changing resistance on the current in a circuit. yy Calculate the resistance, voltage and current from Ohm’s law (V=IR) including potential drop, graph of ohmic and non-ohmic conductors. yy Describe the variation of current with voltage in a range of devices (e.g, resistors, filament bulbs, diodes, light dependent resistors (LDRs) and thermistors). yy Explain that voltage is the energy transferred per unit charge. yy Calculate power, voltage and current using P=IV. (ii) Electromagnetic effects yy Explain the working of simple a.c. generators and transformers. yy Calculate the voltages across the coils in a transformer from the numbers of turns in the coils. yy Describe transfer of energy from power stations to consumers. yy Explain that electricity is transferred at high voltages in power supply systems. yy Explain the use of a.c. in power supply systems. m a te r ia l yr ig h t e d cop v  Table of Content 4. Waves (i)The electromagnetic spectrum yy Name the different components of the electromagnetic spectrum: radio waves, microwaves, infrared, visible light, ultraviolet waves, X-rays and gamma rays. yy Describe the uses of microwaves, infrared and ultraviolet waves and their potential dangers. yy State some uses of X-rays and gamma rays in medical field. yy Explain the transfer of information along optical fibres. yy Explain that radio waves, microwaves, infrared and visible light carry information over large and small distances, including global transmission via satellites. yy Describe the ways in which reflection, refraction and diffraction affect communication. yy Describe the difference between analogue and digital signals and that more information can be transmitted using digital signals. 5. The Earth and beyond yy Explain that gravity acts as a force throughout the universe. yy Describe evolution of stars over a long timescale. yy Describe the search for evidence of life elsewhere in the universe. yy Describe ideas and evidences (e.g. microwave background, red shift) used to explain the origin and evolution of the universe. m a te r ia l yr ig h t e d vi cop   Assessment Assessment in science involves detailed process of measuring students’ achievement in terms of knowledge, skills, and attitude. The progress of learning is inferred through analysis of information collected. The accuracy and objectivity of assessment determines its validity. The modality and components of assessment should be clearly conveyed to the students. The teacher’s expectations should be made clear to students and appropriate learning outcomes should be set. The teachers can play an important role in the students’ achievement by effectively monitoring their learning, and giving them constructive feedback on how they can improve, and provide the necessary scaffolding for the needy learners as identified through reliable assessment techniques and tools. Purpose of Assessment Assessment is used to: inform and guide teaching and learning: A good assessment plan helps to gather evidences of students’ learning that inform teachers’ instructional decisions. It provides teachers with information about the performance of students. In addition to helping teachers formulate the next teaching steps, a good classroom assessment plan provides a road map for students. Therefore, students should have access to the assessment so they can use it to inform and guide their learning. help students set learning goals: Students need frequent opportunities to reflect on what they have learnt and how their learning can be improved. Accordingly, students can set their goals. Generally, when students are actively involved in assessing their own next learning steps and creating goals to accomplish them, they make major advances in directing their learning. assign report card grades: Grades provide parents, employers, other schools, governments, post-secondary institutions and others with summary information about students’ learning and performances. motivate students: Students are motivated and confident learners when they experience progress and achievement. The evidences gathered can usher poor performers to perform better through remedial measures. The achievements and performances of the learners in physics are assessed on the following three domains: Scientific knowledge: Basic knowledge and understanding of energy and work, force and structures, electricity and magnetism, sound and light, thermodynamics, modern physics and inter-relationship of physical science m a te r ia l Reprint 2018 yr ig h t e d cop vii  Table of Content with other branches of science, and their attributes to people and environment. Working scientifically: Basic understanding of the nature of science, and how science works. Demonstration of logical and abstract thinking and comprehension of complex situations. Explore how technological advances are related to the scientific ideas underpinning them. Compare, contrast, synthesize, question and critique the different sources of information, and communicate their ideas clearly and precisely in a variety of ways, including the use of ICT. Scientific values and attitudes: Consider the power and limitations of science in addressing social, industrial, ethical and environmental issues, and how different groups in the community and beyond may have different views about the role of science. They make informed judgments on statements and debates that have a scientific basis, and use their learning in science for planning positive action for the welfare of themselves, others in their community and the environment. The Assessment Process Effective classroom assessment in Science: assesses specific outcomes in the program of studies. the intended outcomes and assessment criteria are shared with students prior to the assessment activity. Assessing Student Learning in Classroom Assessing, Evaluating & Communicating What will be the next What will Planning steps in learning? students self / teacher reflection learn? goal setting How will students receive summative feedback? How will we know qualitative / descriptive learning has occured? quantitative / marks criteria / indicators self / teacher as judge Program of exemplars assessment OF learning Studies : Learner How will students receive Outcomes ongoing formative feedback? descriptive specific self / peer / parent / mentor teaher as coach assessment FOR learning How will we collect evidence of learning? purpose and contex What will be the next demostration of learning steps in learning? - observation - learning log - performance tasks How will students - projects demostrate their What activities will - tests learning? enable students to - written language learn? - oral language - visual communication m a te r ia l Reprint 2018 yr ig h t e d viii cop   assesses before, during and after instruction. employs a variety of assessment strategies to provide evidence of students’ learning. provides frequent and descriptive feedback to students. ensures students can describe their progress and achievement, and articulate what comes next in their learning. informs teachers and provides insight that can be used to modify instruction. Scheme of assessment in science The following schemes of assessment are used to assess students’ performance: 1. Continuous Formative Assessment (CFA) Formative assessment is used to provide feedback to teachers and students, so that teaching and learning can be improved through the provision of regular feedback and remedial learning opportunities. It also enables teachers to understand what teaching methods and materials work best. CFA facilitates teachers to diagnose the learning needs of learners and recognize the individual differences in learning. Through the constructive feedback, students are able to understand their strengths and weaknesses. It also empowers them to be self-reflective learners, who monitor and evaluate their own progress. CFA should happen daily throughout the teaching-learning processes of the academic year. It is NOT graded, as it is only to give continuous feedbacks to the students. 2. Continuous Summative Assessment (CSA) Continuous Summative Assessment is another form of continuous assessment (CA). It helps in determining the student’s performance and the effectiveness of instructional decisions of teachers. The evidences from this assessment help students to improve learning, and mandate teachers to incorporate varied teaching strategies and resources to ensure quality teaching and learning in the science classes. This assessment also empowers students to be self-reflective learners, who monitor and evaluate their own progress. In CSA, the students’ performances and achievements are graded. This ensures active participations of learners in the teaching and learning processes. m a te r ia l Reprint 2018 yr ig h t e d cop ix  Table of Content 3. Summative Assessment (SA) Summative assessment (SA) is conducted at the end of the first term and at the end of the year to determine the level of learning outcomes achieved by students. The information gathered is used by teachers to grade students for promotion, and to report to parents and other stakeholders. The identified techniques for SA are term examinations - first term and annual examinations. The questions for the term examinations should cover all the three domains of science learning objectives, using the principles of Bloom’s taxonomy. Assessment Matrix Types of CFA CSA SA assessment Definition It is a continuous process of assessing It is a continuous process of grading Assesses student’s student’s problems and learning needs and student’s performances and achievements. cumulative to identify the remedial measures to improve Teachers provide feedbacks for performances and student’s learning. It also enables teachers improvement. It also enables teachers to achievements at the to understand what teaching methods and understand what teaching methods and end of each term. materials work best. materials work best. Scientific Working Scientific Scientific Working Scientific SK, WS SK, WS Domains knowledge scientifically values and knowledge scientifically values and & SV & SV (SK) (WS) attitudes (SK) (WS) attitudes (SV) (SV) Quiz & Immediate Observation Home work Practical Project Work. Techniques debate,class interaction of student’s and work Term Term presentation, with conduct, in chapter end exam. exam homework, students, group work, test. class work, class work, field trip, immediate home work, excursion, interaction experiments, etc. with exhibition, students. case studies Assessment Q&A, Checklist and Checklist Rubrics Rubrics Rubrics Paper Paper Tools checklist anecdotal and (HW) and (Practical (Project pencil pencil and records. anecdotal paper work) work) test test anecdotal records. pencil test records. (Chapter end test). Frequency Checklists and anecdotal records must be HW-for Practical Project Work Once in Once in a interval maintained for each topic throughout the every work –Once for a term. year. (when academic year. chapter, once in the whole &how) Chapter each term year but end test – assessed for every two times chapter. (half yearly) Format in SK WS SV Mid- Annual Progress Term Exam Report Weightings T1= 2.5 T1= 5 T1= 2.5 T1=30 T2=50 T2= 2.5 T2= 5 T2= 2.5 m a te r ia l Reprint 2018 yr ig h t e d x cop   Assessment Techniques and Tools The following techniques and tools are used in assessing students’ performance with objectivity. 1. Observation Check list Observing students as they solve problems, model skills to others, think aloud during a sequence of activities, or interact with peers in different learning situations provides insight into student’s learning and growth. The teacher finds out under what conditions success is most likely, what individual students do when they encounter difficulty, how interaction with others affects their learning and concentration, and what students need to learn next. Observations may be informal or highly structured, and incidental or scheduled over different a period in different learning contexts. Observation checklists are tools that allow teachers to record information quickly about how students perform in relation to specific outcomes from the program of studies. Observation checklists, written in a yes/no format can be used to assist in observing student performance relative to specific criteria. They may be directed toward observations of an individual or group. These tools can also include spaces for brief comments, which provide additional information not captured in the checklist. Tips for using Observation Checklists i. Determine specific outcomes to observe and assess. ii. Decide what to look for. Write down criteria or evidence that indicates the student is demonstrating the outcome. iii. Ensure students know and understand what the criteria are. iv. Target your observation by selecting four to five students per lesson and one or two specific outcomes to observe. Date all observations. v. Collect observations over a number of lessons during a reporting period and look for patterns of performance. vi. Share observations with students, both individually and in a group. Make the observations specific and describe how this demonstrates or promotes thinking and learning. vii. Use the information gathered from observation to enhance or modify future instruction. m a te r ia l Reprint 2018 yr ig h t e d cop xi  Table of Content Sample Checklist Name Topic: Pressure Teacher’s com- Scientific knowledge Working scientifically Scientific values ments Demonstrates concern for oneself and Explains pressure and thrust per unit Lists down the significance of experimental Handles equipment, apparatuses, Demonstrates ability to set up State Pascal’s Law and describe its Respects others ideas and views Shows curiosity to learn science pressure in our daily lives and chemical safely. correct experiments. applications procedures. Follows others area Tandin Tshering 2. Anecdotal notes Anecdotal notes are used to record specific observations of individual student behaviours, skills, and attitudes in relation to the outcomes of the science teaching and learning process. Such notes provide cumulative information on students’ learning and direction for further instruction. Anecdotal notes are often written as ongoing observations during the lessons, but may also be written in response to a product or performance of the students. They are generally brief, objective, and focused on specific outcomes. The notes taken during or immediately following an activity are generally the most accurate. Anecdotal notes for a particular student can be periodically shared with the student, or be shared at the student’s request. The purpose of anecdotal notes is to: provide information regarding a student’s development over a period of time. provide ongoing records about individual instructional needs. capture observations of significant behaviours that might otherwise be lost. Tips for maintaining Anecdotal Notes i. Keep a notebook or binder with a separate page for each student. Write the date and the student’s name on each page of the notebook. m a te r ia l Reprint 2018 yr ig h t e d xii cop   ii. Following the observations, notes are recorded on the page reserved for that student in the notebook. iii. The pages may be divided into three columns: Date, Observation and Action Plan. iv. Keep notes brief and focused (usually no more than a few sentences or phrases). v. Note the context and any comments or questions for follow-up. vi. Keep comments objective. Make specific comments about student strengths, especially after several observations have been recorded and a pattern has been observed. 3. Project work Project work is one of the best ways to practice the application of scientific conceptual ideas and skills. The very purpose of including project work is to provide opportunity to explore and extend their scientific knowledge and skills beyond the classroom. Students learn to organize, plan and piece together many separate ideas and information into a coherent whole. Through project work, students learn various scientific techniques and skills, including data collection, analysis, experimentation, interpretation, evaluation and drawing conclusion; and it fosters positive attitude towards science and environment. The science curriculum mandates students to carry out project work to help them to: i. develop scientific skills of planning, designing and making scientific artefacts, carrying out investigations, observation, analysis, synthesis, interpretation, organization and recording of information. ii. enhance deeper understanding of social and natural environment. iii. develop student’s ability to work in group and independently. iv. provide opportunity to explore beyond the classroom in enhancing their scientific knowledge and skills, which will contribute towards the development of positive attitudes and values towards science and environment. v. understand how science works and the nature of scientific knowledge. vi. develop oral and written communication skills. Teachers can facilitate students to carry out the project work by considering the following suggested guidelines. Allow students to select their own project ideas and topics. Encourage students to be scientifically creative and productive. Provide a clear set of guidelines for developing and completing projects. Help students to locate sources of information, including workers in science- m a te r ia l Reprint 2018 yr ig h t e d cop xiii  Table of Content related fields who might advise them about their projects. Allow students the option of presenting their finished projects to the class. Inform students about the general areas on which assessment may be made. For example, scientific content or concepts, originality of ideas, procedures, and the presentation. Advice students to contact their teacher for further assistance or consultations, for, students must be closely guided by the teacher starting from the selection of the topic, doing investigations, data collection, and analysis to writing report in a formal style. Each student is assigned a Project Work for the academic year. The project work is assessed out of 28 marks, which should be converted out of 5 marks for the whole year. Students can share their project work findings, either in the form of class presentation or display. At the end of the project work, every student must prepare a project work report, about 2000 to 2500 words, in the formal format, suggested in the following section. The product of the project work must be inclusive of write ups, illustrations, models, or collection of real objects. Following are some of the useful steps that students may follow. 1. Select a topic for the science project The first step in doing science project is selecting a topic or subject of your interest. Teachers guide students in identification and selection of the topic. The concerned teacher has to approve the topic prior to the commencement of the project work. 2. Gather background information Gather information about your topic from books, magazine, Internet, people and companies. As you gather information, keep notes from where you got the information as reference list. 3. Write your hypothesis Based on your gathered information, design a hypothesis, which is an educated guess in the form of a statement, about what types of things affect the system you are working with. Identifying variables is necessary before one can make a hypothesis. For example, depth of the fluid affects the fluid pressure. Develop a research question supported by a few questions to test your hypothesis. For example, how does the depth of fluid affect the pressure? Sub-questions may include, what is the fluid pressure at the same depth at different points? What is the fluid pressure as the depth increases? 4. Identify variables The hypothesis and the research questions should guide you to identify m a te r ia l Reprint 2018 yr ig h t e d xiv cop   the variables. When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes, variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other. 5. Design an experiment or observation method Having made the hypothesis, design an experiment to test the hypothesis and devise the method of observation. Make a systematic list of what you will do or observe to answer each question. This list is known as experimental or observational procedure. For observations or an experiment to give answers, one must have a “control”. A control is a neutral “reference point” for comparison that allows you to see what changing or dependent variable does by comparing it to not changing anything. Without a control, you cannot be sure what variable causes your observations. 6. Write a list of material Make a list of materials useful to carry out your experiment or observations. 7. Write experiment results Experiments are often done in series. A series of experiments can be done by changing one variable at a time. A series of experiments are made up of separate experimental “runs”. During each run, you make a measurement of how much the variable affected the system under the study. For each run, a different amount of change in the variable is used. This produces a different degree or amount of responses in the system. You measure these responses and record data in a table form. The data from the experiments and observations are considered as a “raw data” since it has not been processed or interpreted yet. When raw data is processed mathematically, for example, it becomes result. 8. Write a summary of the results Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments. It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, one can see trends or patterns that tell you how different variables cause to change the observations. Based on these trends, you can draw conclusions about the system under the study. These conclusions help to confirm or deny your original hypothesis. Often, mathematical equations can be made from graphs. These equations can help you to predict how a change will m a te r ia l Reprint 2018 yr ig h t e d cop xv  Table of Content affect the system without the need to do additional experiments. Advanced levels The Format for Project Work write-up (report) should include the following of experimental science rely heavily on aspects: graphical and mathematical analysis of The title of the project work. data. At this level, science becomes even Acknowledgement: Show courtesy to more interesting and powerful. thank the people and organizations for the help received. 9. Draw conclusions Table of content. Using the trends in your experimental data Introduction: What is the topic about, and and your experimental observations, try why was the topic chosen? hypothesis, research question. to answer your original questions. Is your Background information: Scientific hypothesis correct? Now is the time to concepts, principles, laws and pull together what happened in the form of information on the topic. conclusion, and assess the experiments you Methodology: Methods of data collection did. Describe, how variables have affected – sampling, tools used, etc; data sorting. Data analysis: Data tabulation, data the observations, and synthesize a general processing, findings, etc. presented statement. For example, the pressure for the in a logical order with illustrations, same fluid increases with the increase of photographs, and drawings where depth! appropriate and necessary to support the findings. 10. Write a report on the project Conclusion: Reflection of the findings, Having completed all the steps of learner’s experiences and opinions experiment and investigation with regarding the project. appropriate results and conclusion Bibliography: List of the sources of the information. drawn, the last thing is to write a report. The report should start with an introduction on the topic related to your hypothesis, purpose of the study, literature review, methods used, findings, and conclude with conclusions. Do not forget to acknowledge the support provided by all individuals and organizations. Write a bibliography to show your references in any form. Such information includes the form of document, name of writer, publisher, and the year of publication. The teacher uses the “Rubric for the Project Work” given below to assess the student’s project work. Random viva voce is necessary to guide and support students’ work during the course of project work. m a te r ia l Reprint 2018 yr ig h t e d xvi cop   Criteria for the Project Work Criteria Background Experimental Total Problem Format Bibliography scores Name research and design / Investigation Analysis and (4) on the (28) hypothesis (4) (4) editing hypothesis materials / (4) (4) (4) procedure (4) Nima Dawa Rubrics for the Project Work Scoring Total Criteria Score 4 3 2 1 (28) Problem and Problem is new, Problem is Problem is Problem is meaningful and not new but stated but not stated Hypothesis well researched. meaningful. neither new nor and meaningful. Hypothesis is Hypothesis is Hypothesis clearly stated clearly stated. Hypothesis is unclear. in the “IF... is not clearly THEN” format. stated. Background Research is Research is Research is not Research research on the thorough and thorough but thorough and not thorough hypothesis specific. not specific. not specific. and All the ideas Most ideas are Few ideas are Ideas are not are clearly explained. explained. explained. explained. Experimental Procedure is Procedure is Procedure is A few steps detailed and detailed but not not detailed of procedure design / sequential. sequential. and not are listed. materials / sequential. All materials Most materials Materials procedure are listed. are listed. Few materials list is are listed. absent. Safety issues Safety issues have been have been Few safety Safety issues addressed. addressed. issues have are not been addressed. addressed. m a te r ia l Reprint 2018 yr ig h t e d cop xvii  Table of Content Scoring Total Criteria Score 4 3 2 1 (28) Investigation Variables have Variables have Variables have Missing two been identified, been identified somewhat or more of controls are and controls are been identified, the variables appropriate and appropriate but controls are or the explained. not explained. somewhat controls. known. Sample size is Sample size is Sample appropriate and appropriate. Sample size is size is not explained. not appropriate. considered. Data collected Data collected from at least 3 Data collected Data from at least 4 sources from at least 2 collected sources. sources. from only 1 source. Analysis& Appropriate Appropriate No appropriate No conclusion tool used for tool used for tool used for appropriate analysis. analysis. analysis. tool used for analysis. Explanation is Conclusions Not enough made for how are supported explanation is Not enough or why the by the data. made for how explanation hypothesis was or why the is made for Not enough supported or hypothesis was acceptance explanation is rejected. supported or and made for how rejected. rejection of Conclusion is or why the hypothesis. supported by hypothesis was Conclusion is the data. supported or not appropriate. Conclusion rejected. is absent. Reflection is Reflection is stated clearly. Reflection is not clear. Reflection is stated. not stated. Format and Correct format Only one aspect Only two Three editing followed of format is aspects of or more throughout. incorrectly format are aspects of done. incorrectly format are Report is free done. missing. of errors in Report contains grammar, a few errors Report contains Report spelling or in grammar, some errors contains punctuation. spelling, and in grammar, many errors punctuation. spelling, in grammar, punctuation spelling, and punctuation. m a te r ia l Reprint 2018 yr ig h t e d xviii cop   Scoring Total Criteria Score 4 3 2 1 (28) Bibliography Five or more Three or four One or two No references are references references references cited in APA are cited and are cited and made. format and referenced referenced referenced throughout throughout throughout the paper and the paper and the paper and presentation. presentation. presentation. TOTAL SCORE 4. Practical Work Learning by doing is fundamental to science education. Practical work is one of the means that helps students to develop their understanding of science, appreciate that science is evidence driven and acquire hands-on skills that are essential to science learning and in their future lives. The practical work as defined by SCORE (2009a) is ‘a “hands-on” learning experience which prompts thinking about the world in which we live’.Therefore, the purposes of doing practical in science classes are to – i. help students to gain or reinforce the understanding of scientific knowledge. ii. develop students’ understanding of the methods by which the scientific knowledge has been constructed. iii. increase a student’s competence to engage in scientific processes such as in manipulating and/or observing real objects and materials with due consideration for safety, reliability, etc. iv. develop technical and scientific skills that improve science learning through understanding and application. v. develop manipulative skills, knowledge of standard techniques, and the understanding of data handling. vi. Inculcate excitement of discovery, consolidation of theory, and the general understanding of how science works. Practical work is integral to the aspects of thinking and working scientifically in science, and must be built in as a full learning experience for students. Students are engaged in a range of practical activities to enable them to develop their understanding through interacting with apparatus, objects and observations. The assessment of students’ scientific skills and their understanding about the scientific processes through practical work is crucial in the process of science learning. To ensure the validity, assessment needs to sample a range of activities in different contexts; and reliability is ensured through the appropriate moderation procedures so that fairness in assessment is maintained. m a te r ia l Reprint 2018 yr ig h t e d cop xix  Table of Content The new science curriculum envisages that students are given the opportunity to undertake work in which they make their own decisions. They should be assessed on their ability to plan, observe, record, analyze, communicate and evaluate their works. To ensure that the assessment in the practical is evidence-based and objective, rubrics is used. The rubrics are scored out of 16, which must be reduced to 5% each for the two terms. Criteria for the Practical Work Criteria Scientific Total scores Name operation & Results & data Analysis & Conclusions (4) (16) report format representation (4) discussion (4) (4) Sonam Wangmo Rubrics for the Practical Work Criteria Scoring Total Score (16) 4 (Very good) 3 (Good) 2 (Fair) 1 (Poor) Purpose is clear Purpose is clear Purpose is inac- Purpose is vague purposeful. purposeful. curate, general or or inaccurate. Scientific All the pro- All the procedures are extraneous. Procedures are operation cedures are followed but not done A few procedures are not followed followed system- systematically. skipped. Safety atically. Work is carried out Safety procedures procedures Full attention is with some attention were frequently are ignored given to relevant to relevant safety ignored completely. safety for oneself procedures. and others. Results & data Representation Representation of the Representation of Representation representation of the data/ data/results in tables the data/results in of the data/ results in tables and graphs with some tables and graphs results in tables and graphs with error in units of mea- numerous error in and graphs are correct units of surement. units of measure- not relevant. measurement. Transformations in ment. Transformations Transformations some of the results/ Transformations in in the results/ in the results/data data are evident. most of the results/ data are not are evident. Graphs and data are not evident. evident. Graphs and tables are scaled Graphs Some attempts tables are scaled correctly with and tables are evident to correctly, with appropriate titles are scaled produce graphs appropriate titles but no labels. correctly, from the data/ and labels. but without results. appropriate titles and labels. m a te r ia l Reprint 2018 yr ig h t e d xx cop   All the tools used Most of the tools used Only a few tools are No appropriate Analysis & for analysis are for analysis are ap- used for analysis. tools are used for discussion appropriate. propriate. A comprehen- analysis. A comprehensive A comprehensive sive discussion, Comprehensive discussion, discussion, containing containing a few discussion is containing a com- some comparative comparative analysis absent. parative analysis analysis is evident. is evident. The experimental is evident. The experimental The experimental findings have no The experimental findings do not have findings have weak significance to findings are strong significance significance to the the purpose of significant to the to the purpose of the purpose of the the experiment. purpose of the experiment. experiment. experiment. Conclusions are Conclusions are drawn Conclusions are No valid conclu- drawn from the from the findings but not drawn from the sions drawn from Conclusions findings and are less significant to objec- findings and have the findings. significant to tives of the experiment. no significance to Limita- objectives of the Limitations of experi- objectives of the tions of experiment. ment are identified. experiment. experi- Limitations of Some limitations ment are experiment are of experiment are not identi- identified, and identified. fied. ways to improve are evident. TOTAL SCORE m a te r ia l Reprint 2018 yr ig h t e d cop xxi Chapter-wise Weighting and Time allocation Maximum time required Chapters Chapter title Weighting (%) (mins) Chapter 1 Forces and Motion 605 14% Chapter 2 Pressure in Fluids 432 10% Chapter 3 Energy 950 22% Chapter 4 Electricity and Magnetism 950 22% Chapter 5 Waves 605 14% Chapter 6 The Earth and Beyond 778 18% Total 4320 100% The total time required to complete the topics is 4320 minutes or 96 periods of 45 minutes in a period. m a te r ia l Reprint 2018 yr ig h t e d cop Contents Chapter 1: Forces and Motion 1 1. Gravitational Force 1 A. Centre of Gravity and stability of bodies 2 B. Equilibrium 5 2. Moment of Force 8 A. Forces and equilibrium 8 B. Couple 11 C. Principle of moments 12 3. Falling Objects 15 A. Force on falling objects 15 Chapter 2: Pressure and its Applications 23 1. Pressure 23 A. Thrust on a surface area 23 B. Body in a fluid 28 2. Transmission of Pressure inside a liquid 31 A. Pascal’s law 31 B. Application of Pascal’s law 31 Chapter 3: Energy 41 1. Work and Energy 41 A. Work and Power  42 B. Energy 49 2. Energy Conservation 55 A. Sustainable use of energy 55 m a te r ia l Reprint 2018 yr ig h t e d cop Table of Content Chapter 4: Electricity & Magnetism 73 1. Electric Circuits 73 A. Flow of electric current 73 B. Ohm’s Law 77 C. Heating effect of current 86 2. Electromagnetic Effects 90 A. Electromagnetic induction 90 Chapter 5: Waves 105 1. The Electromagnetic Spectrum 105 A. Types of electromagnetic waves 107 2. Communication through Waves 113 A. Communication over short distances 113 B. Communication over long distances 115 C. Communication through sound waves 117 D. Analogue and digital signals 119 Chapter 6: The Earth and Beyond 127 1. Gravity and Universe 127 A. Gravitational force 127 B. The role of gravity in universe 133 2. Evolution of Stars and Galaxies 140 A. Cosmic Microwave Background and Redshift 141 B. Evidence of life elsewhere in the universe 145 Specimen Question Paper 155 Glossary 165 m a te r ia l Reprint 2018 yr ig h t e d b cop  1 FORCES AND MOTION E arth attracts everything towards its centre. This force of attraction of the Earth is called gravitational force. The weight of all bodies is due to the gravitational pull of the Earth. All kinds of bodies have a point on them through which the entire weight of an object appears to act. The stability of bodies depends on the position of this point. This point is called centre of gravity. Statics is a branch of mechanics which deals with the system in equilibrium. A system is said to be in equilibrium if there is no resultant force and no resultant moment. Resultant force displaces a body in linear direction, while resultant moment makes a body rotate in either clockwise or counter clockwise direction. When objects fall freely, they experience various forces. The forces acting on falling objects change with velocity. When the resultant force on the falling objects become zero they attain maximum velocity called terminal velocity. 1. Gravitational Force Learning Objectives On completion of this topic, you should be able to: describe gravitational field. define centre of gravity of an object. explain the stability of a body. Do you ever wonder how moon remains in place around the Earth in space? Sir Isaac Newton discovered that all the objects have mass and attract each other with certain amount of force called gravity. Every object around you attract each other with the force of gravity. However, this force is very negligible that it is not felt. The force acting between these bodies is determined by their masses and the distances m a te r ia l Reprint 2018 yr ig h t e d cop Chapter 1 between them. The region around a body where force of attraction is felt is the gravitational field of the body. The body with larger mass will have more gravity and larger gravitational field. For example, an aeroplane has more gravitational force of attraction than a car. Similarly, the Moon has less gravitational force and field than the Earth. The gravitational force of attraction is greater if the bodies are closer. A. Centre of gravity and stability of bodies The Earth pulls every mass towards its centre. This force is referred to as weight. The larger mass has more weight. Our body is a matter made up of tiny particles with individual mass. Each of these small mass has weight. Therefore, the total weight must act downward as if the whole weight is located at a single point. Activity 1.1 Locating centre of gravity of a body Materials required: A paper card board of uniform thickness, nails, retort stand with clamp, small weight or stone, thread, cork, pencil, ruler, and scissors. Precaution H1 Be careful while using knife and sharp objects. H2 H3 Procedure Figure 1.1 Step 1  Cut out an irregular shaped lamina from a paper cardboard, similar to the one in Figure 1.1. Step 2  Using the nail; make three holes (H , H and H ) on the lamina near the edge as shown in Figure 1.1. 1 2 3 Step 3  Tie a small weight or a stone to the end of a thread to make a major plumb line. Cork pivot Mini Nail H1 plumb lines Cardboard plate Thread Stand H2 H3 Weight Figure 1.2 Figure 1.3 m a te r ia l Reprint 2018 yr ig h t e d 2 cop  Forces and Motion Step 4  Make mini plumb lines by tying thread to the tail of small arrows made up of card board. Step 5  Fix the mini plumb lines at different locations on the lamina as shown in Figure 1.2. Step 6  Pierce a nail through a cork and clamp it on the retort stand to set up a pivot as shown in Figure 1.3. Step 7  Hang the lamina on the pivot at hole H. 1 Suspend the plumb line from the pivot at H. Slightly displace the Step 8  lamina 1 and release it. Allow it to swing freely until it comes to rest. After it comes to rest, mark three dots at three different locations on the lamina, directly behind the thread of the plumb line. Step 9  Remove the plumb line and the lamina from the pivot and join the three dots with a straight line using a ruler. Repeat steps 7 to 9 through hole H. Mark the point of intersection of Step 10  the two lines as G. 2 Step 11  Hang the lamina at hole H , and repeat steps 8 and 9. 3 Step 12  Try to balance the lamina at G on the tip of a drawing pin as shown in Figure 1.4. G Pin Answer the following questions. Figure 1.4 1. What do mini plumb lines represent? 2. What are the directions of mini plumb lines when the lamina hangs from holes H1, H2 and H3? 3. What conclusion would you draw from the behaviour of mini plumb lines? 4. What does the major plumb line represent? 5. Did the third line intersect at G? Why? 6. What does G represent? 7. Did the lamina balance at point G? 8. Where would the line drawn intersect if we hang lamina by any other point H4? 9. What conclusion can you draw from the experiment? m a te r ia l Reprint 2018 yr ig h t e d cop 3 Chapter 1 10. Locate the point of balance (point G) for the lamina given in Figure 1.5. A B C D E F Figure 1.5 In Activity 1.1, we find that the irregular paper board lamina balances on the single point G and the whole weight of the paper board lamina appear to act from point G, even though the Earth attracts every part of plate at different locations. Thus, a point on a body through which the whole weight of a body appears to act is known as Centre of Gravity of the body. It is usually represented as ‘C.G’. The point can be either within or outside the body. A bowl usually do not tumble easily compared to a tumbler kept on the same surface level. This is because a bowl is more stable than the tumbler. The stability of a body is determined by its position of centre of gravity. The stability of a body is determined by the following: (a) Position of C.G. of a body The stability of a body depends upon its position of centre of gravity (C.G.). The body is more stable if the position of C.G. is at its lower part. Let us consider an empty container A as shown in Figure 1.6(a). In this case, the C.G. is somewhere at the middle and the container is stable. When the bottom compartment of the same container is filled with marbles as in Figure 1.6(b), the position of C.G. is lowered and the container becomes more stable. Similarly, if the middle compartment of the same container is filled with marbles as in Figure 1.6(c), the position of the C.G. is raised higher. Hence the body becomes unstable. Now, if the topmost compartment of the same container is filled with marbles as shown in Figure 1.6(d), then the position of C.G. is raised even higher than in m a te r ia l Reprint 2018 yr ig h t e d 4 cop  Forces and Motion third case. Hence the body becomes more and more unstable. C.G. C.G. W C.G. W C.G. W W B.S. B.S. B.S. B.S. (a) (b) (c) (d) Figure 1.6 (b) Area of the Base of Support (B.S.) The surface area in contact with another surface which supports a body is the area of base of support. A B C D For example, State A of the upright bottle in Figure 1.7 has larger B.S. than the bottle upside down in State B, thus making State A of bottle more C.G. C.G. C.G. C.G. stable than State B. Even when bottle in State A is slightly tilted W W W W as shown in state C, the bottle do not tumble because the line of gravity due to the weight of B.S. B.S. B.S. B.S. body acts vertically downward through its base. In case of State Figure 1.7 B, the B.S. is narrow and on slight disturbance as shown in state D, the line of gravity due to the weight of body will not act through the base of the bottle, making it tumble. The stability of a body depends upon the position of C.G. and the area of B.S. B. Equilibrium When a body is balanced, it is said to be in equilibrium. If a force is applied to a body in equilibrium, the body either tilts, topples or rolls. Therefore, the equilibrium of a body is categorised in the following states. m a te r ia l Reprint 2018 yr ig h t e d cop 5 Chapter 1 (i) Stable Equilibrium A body is said to be in stable equilibrium when a body has an ability to regain its original position even when displaced by an external force. This state is achieved when the line of gravity due to the weight of body acts vertically downward through its B.S., at all positions. The body becomes more stable when the position of C.G. is lowered. For example, a cone in Figure 1.8(a) is in stable equilibrium. The C.G. rises when the tip of the cone is slightly pushed, however, the line of gravity due to the weight of the body still passes through its B.S. In such state, when the cone is released C.G. brings it back to its initial position. C.G. C.G. C.G. W B.S. B.S. B.S. (a)Stable Equilibrium (b) Unstable Equilibrium (c) Neutral Equilibrium Figure 1.8 (ii) Unstable Equilibrium A body is in state of unstable equilibrium when the line of gravity of its weight falls outside the B.S. on slight displacement and it loses its ability to regain its original position. In this condition, the body takes up new position. A body with narrow B.S. and C.G at high position is usually unstable. For example, a cone in Figure 1.8(b) is in unstable equilibrium. The C.G. of the cone is at the highest point. When the cone is slightly pushed the line of gravity due to the weight of the body no longer passes through its B.S.,therefore, the cone topples. In such state, the cone takes up new position which has lower C.G. (iii) Neutral Equilibrium If a body neither takes a new position nor regains its original position when displaced slightly by an external force, then the body is said to be in neutral equilibrium. In this case, the position of the C.G. and B.S. do not change when displaced. For example, a cone in Figure 1.8(c) is in neutral equilibrium. When the cone is pushed, the position of C.G. remains at the same level. In such state, the cone does not take up new position. Similarly, if a ball is pushed slightly to roll over a horizontal surface, it will not come back to its original position and C.G. of the ball is neither raised nor lowered. m a te r ia l Reprint 2018 yr ig h t e d 6 cop  Forces and Motion Questions 1. Why would you advice a person to sit rather than stand in a moving bus? 2. “The centre of gravity of a body may not be necessarily on the body”. Justify. 3. Why do dzongs have broader base? http://alexei.nfshost.com/PopEcol/lec9/equilib.html http://www.citycollegiate.com/staticsXb.htm https://www.youtube.com/watch?v=muM4hhwqEwE m a te r ia l Reprint 2018 yr ig h t e d cop 7 Chapter 1 2. Moment of Force Learning Objectives On completion of this topic, you should be able to: describe statics, and system in equilibrium. describe resultant, moment and parallelogram law of forces. explain the couple, torque of a couple and the principle of moments. A. Forces and equilibrium The simple descriptions of motion that we have used so far implicitly treated the motion of only one point in a body. It is a good description provided that all points in the body follow similar, parallel paths. This kind of motion is called pure translational motion. Along with translational motion, a body can also execute rotational motion (like that of a spinning wheel) and vibrational motion (like that of a shaking jelly). A body which cannot vibrate noticeably is said to be rigid; its shape and size do not change significantly when it is acted on by a system of forces. Therefore, the general kind of motion of a rigid body is a combination of translation and rotation. For example, the flight of boomerang executes translational motion due to its rotation. A couple of forces may act on a body at a same time at different or same lines of action. Figure 1.9(a) shows two forces; 8 N and 10 N, acting on a rigid body in straight line in the same direction. The total magnitude of these two forces on the body is numerically equal to the sum of the magnitudes of these individual forces and the body moves in the direction of the greater force. The net force of these forces is referred to as resultant force. The resultant force in case of Figure 1.9 (a) is 18 N and the rigid body moves in the direction of the greater force, 10 N. Resultant Force= 18 N Resultant Force= 2 N 8N 10 N 8N 10 N (a) (b) Figure 1.9 If two equal forces act in opposite direction in the same line of action, as shown in Figure 1.9 (b), then the magnitude of resultant force is equal to the difference of the magnitude of two forces, i.e., 2N and the body moves in the direction of the greater force, 10 N. m a te r ia l Reprint 2018 yr ig h t e d 8 cop  Forces and Motion When a couple of forces act on a non-rigid (elastic) body, the resultant force generally tends to change the dimension of the body and at the same time, it may execute rotational, translational and vibrational motion. For example, bouncing of a soft rubber ball undergoes all these motions. A rigid body which is currently stationary will remain stationary if the resultant force is zero for all the forces applied on it. Similarly, a moving rigid body will remain in uniform motion if the resultant force is zero for all the forces applied on it. In both the cases, the body is said to be in equilibrium. Statics is a branch of mechanics that deals with the study of forces in equilibrium. The general conditions for equilibrium are as follows: (i) The total force must be zero. (ii) The total turning effect of force about any axis must be zero. If a resultant force acts on a body then that body can be brought into equilibrium by applying an 3N 5 N = additional force that exactly balances this resultant. ltan t su Such a force is called equilibrant and is equal in Re magnitude but opposite in direction to the original 4N resultant force acting on the body. 5 N = nt Force is an influence which causes motion of any uil ibr a q rigid object. Force is a vector quantity, which has E Figure 1.10 both magnitude and direction. Hence, it follows all the properties of vectors, such as vector addition and vector subtraction. One of the vector addition technique is known as the parallelogram law of vector addition. It is a graphical representation of vectors that is used to determine the magnitude and direction of the resultant vector. This method can be easily used to determine the magnitude and direction of the resultant force. Activity 1.2 Verifying the law of parallelogram of forces Materials required: A drawing board, a sheet of plain paper, pencil, protractor, drawing pins. Procedure Step 1  Using board. the drawing pins, mount the sheet of plain paper on the drawing m a te r ia l Reprint 2018 yr ig h t e d cop 9 Chapter 1 Step 2  Consider two force vectors A of 10 N and B of 5 N. Draw arrows to represent these forces in such a way that these force vectors are tail to tail in contact with each other and inclined to each other at an angle of 500. Let.1 cm = 1 N of force as shown in Figure 1.11. Step 3  Complete the parallelogram by drawing these vectors as adjacent sides of the parallelogram. Step 4  Now draw the diagonal originating from the touching tails. The diagonal represents the resultant force vector. Note the magnitude of resultant force. A B A B A and B are the force vectors to be added A and B are arranged as per Step 2 and parallelogram is completed A A +B R= Diagonal arrow represents the resultant vector Figure 1.11 B Step 5  Draw an arrow from the tails of the two vectors equal in length as the diagonal but in exactly opposite direction to it. Answer the following questions. 1. Find the resultant of vectors 7 N and 12 N inclined at an angle of 600 with each other. 2. Find the resultant of vectors 5 N and 10 N inclined at an angle of 450 to each other. 3. What are the factors on which the resultant of vectors depend? 4. What does the arrow drawn in step 5 represent? m a te r ia l Reprint 2018 yr ig h t e d 10 cop  Forces and Motion B. Couple If two forces are not acting in a straight line, then the resultant effect of the force is different. For example, when a water tap is turned to open or close, we apply two forces at the two ends of the bip cock. Here the forces are applied simultaneously, parallel and in opposite direction to each other. Thus, it results in rotational motion of bip cock. A few such examples from our day to day activities are shown in Figure 1.12. In these pictures, we use a pair of forces which are parallel to each other, equal in magnitude, and acting in the opposite directions. A pair of equal and parallel forces, acting in opposite directions is called a couple. F F F F d F F Figure 1.12 Couples In Figure 1.12, two equal and opposite forces ‘F’, which are parallel to each other act on a body. The resultant force makes a body turn. The turning effect of a force is known as the moment. If the perpendicular distance between these forces is ‘d’, then the product of the magnitude of one of the forces (F) and the perpendicular distance from the line of action of the forces give the turning effect of the force called moment of couple. The moment of couple is also called torque and is usually represented by ‘τ’ (tau). Mathematically, Moment of couple (τ) = Force (F) x Perpendicular distance (d) between forces. Example 1.1 Two forces each of 20 N is applied to a car steering wheel that has a diameter of 40 cm. If the two forces act tangentially to the steering wheel and in anti-parallel directions calculate the torque applied. Solution: Torque = F x d = 20 N x 0.4 m= 8 Nm m a te r ia l Reprint 2018 yr ig h t e d cop 11 Chapter 1 C. Principle of moments It is everyday experience that the handles on doors are Fulcrum usually located at the outer edge, so that it is easier to open or close. It is difficult to open a door if the handle is located near the hinge, that is, a much larger force is needed to open the same door. Likewise, it is easier to loosen a nut on a bolt by using a long spanner than with a short one. In all these cases, the applied force produces a turning effect Force about a pivot called moment of force. The moment of force is determined by the magnitude of force and distance of the applied force from the pivot. Similar to moment of couple, moment of a force is the product of force and the perpendicular distance of the line of action of force from Figure 1.13 Torque the pivot. Mathematically, Moment of force (τ) = Force (F) x distance from the fulcrum (d) If the force is measured in newton (N) and distance in metre(m), then the unit of moment of force is newton-metre (Nm). The moment of force brings about counter clockwise or clockwise rotation of the body. A body will not turn when it is in equilibrium even when forces act on it about a fixed pivot. This state of equilibrium is explained by the principle of moments. The principle of moments states that the total counter clockwise moment is equal to the total clockwise moment when the body is in equilibrium. In equilibrium, Total Counter Clockwise Moment = Total Clockwise Moment In case of Figure 1.14 d1 d2 Figure 1.14 F1 F2 total counter clockwise moments = total clockwise moments F1 x d1 = F2 x d2 m a te r ia l Reprint 2018 yr ig h t e d 12 cop  Forces and Motion In case of Figure 1.15 d1 d2 d3 F2 F1 Figure 1.15 F3 total counter clockwise moments = total clockwise moments F1 x d1 = (F2 x d2 ) + (F3 x d3) Activity 1.3 Verifying the principle of moments Materials required: A metre ruler, wedge, five weights of 100 g, clamp and stand, and thread. Procedure Step 1  Balance the ruler on the wedge so that it is perfectly horizontal as shown in Figure 1.16. 10 cm x Take two different weights of your Step 2  choice and note down their values as W1 and W2. W1 W2 Figure 1.16 Step 3  Hang 1.16. the two weights on either side of the pivot as shown in Figure Step 4  Adjust the distance of the two weights from the pivot until the ruler becomes perfectly horizontal again. Step 5  Record the distance of the two weights from the pivot. Answer the following questions. 1. Calculate the moment of force in clockwise direction. 2. Calculate the moment of force in counter clockwise direction. 3. Compare the magnitude of moment of force in clockwise direction and counter clockwise direction. 4. What do you conclude from the comparison of clockwise and counter clockwise moments? m a te r ia l Reprint 2018 yr ig h t e d cop 13 Chapter 1 Questions 1. Figure 1.17 shows two forces acting on the edge of a disc making it rotate. Rotating disc 1200 N 0.20 m 1200 N Figure 1.17 a) Define torque of a couple. b) Calculate the torque produced by these forces. 2. Write down five examples of couple. http://www.splung.com/content/sid/2/page/moments http://physicsnet.co.uk/a-level-physics-as-a2/mechanics/moments/ http://www.tutorvista.com/physics/parallelogram-law-of-forces m a te r ia l Reprint 2018 yr ig h t e d 14 cop  Forces and Motion 3. Falling Objects Learning Objectives On completion of this topic, you should be able to: explain that the forces acting on falling objects change with velocity. describe terminal velocity of falling objects. A. Force on falling objects Hundreds of years ago, people thought that the mass or weight of an object was the main thing that determined how fast it would fall. This idea was put forth by the Greek philosopher Aristotle, who said that the speed of a falling object was directly proportional to how heavy it was. Although this seems reasonable at first glance, there are some big problems with this idea. The scientist Galileo Galilei (1564-1642) disproved this idea by showing that objects of the same size and shape but with different masses would hit the ground at the same time when dropped from the same height. Later, Isaac Newton (1643-1727) demonstrated not only which type of object falls fast, but also answered why do objects fall in the first place. Earth exerts a force on all objects near it which causes falling objects to speed up as they fall. He called this force as gravity. Whenever, we describe about falling object, two forces come into picture, namely; the weight of the object and the air resistance. The weight of the object acts downwards. The air resistance is the frictional force acting in the opposite direction to the 0s - 0 m/s movement of the object. 1s - 10 m/s (i) Free falling object 2s - 20 m/s A free falling object is an object that is falling under the sole influence of gravity. Any object that is being acted upon only 3s - 30 m/s by the force of gravity is said to be in a state of free fall. There are two important motion characteristics that are true of free- falling objects: Free-falling objects do not encounter air resistance. 4s - 40 m/s On Earth, all free-falling objects accelerate downwards at a rate of 9.8 m/s2.. A dot diagram of motion of free-falling objects could be used to depict an acceleration of the object. The dot diagram in Figure 1.18 depicts the acceleration of a free-falling object. 5s - 50 m/s l Figure 1.18