okay actually i had a song recommendation but i think in the interest of time we should start first so maybe later if there's a break then i'll play the song that was recommended to me okay so yes i want to start on time so um let me share my slides first all right everybody welcome to the sec 2 science mid-year examination revision session okay so if you are secondary one student okay i mean you can still sit in but of course the topics that i'll be covering today will be different from what will be tested for your exams now okay so this is mainly geared towards the secondary two students who are will be tested on the 2a textbook okay so what will we be covering today we'll be covering chapter 9 forces chapter 10 heat chapter 11 chemical changes and chapter 12 ecosystems and i'll be spending about 15 minutes per chapter okay so unfortunately in the interest of time i can't really like go into the nook and cranny of like each topic okay so this is more of like a brief overview and a revision of all that you've been learning for the past four months in 2022 okay so uh maybe before i even get into teaching right i'll just let you guys know who exactly i am so hi my name is hanjin i'm actually in a lower secondary science tutor here at overmark okay so actually i'm just like you guys i'm still a full-time student actually i'm studying dentistry at nus okay and i've been tutoring for about three plus years since i graduated from my junior college okay so if you guys are interested to know i my secondary school was chongqing high school maine then i graduated um from all levels i went to raffles okay then i graduated and now i'm in nus okay and i'm also currently conducting secondary two group tuitions on the site also it's raining super heavily where i am so maybe you guys might want to tell your parents that you might be waiting there and they might have to keep their clothes okay right so um please stay till the end because there will be a giveaway for the curated notes if you guys are interested in having a copy okay and since this class size is currently so small the chances of you waiting is pretty high okay so i guess if you guys are free just stay till the end right so um just some general tips on how we can prepare ourselves for our examinations okay not just for science but for other topics other subjects as well okay so here are three revision tips that i feel worked very well for me as a student okay so the first one would actually be consolidating information now this is different from just like repeating everything from the textbook into like a piece of muji paper okay i feel like when you want to take notes as a student there's also a right way or a more effective way to do it okay i unfortunately i can't really talk about it today because i don't really have a lot of time okay but i think it's important to consolidate information in the sense that okay you think through what you have learned okay like oh teacher has taught me xyz how can i link it to the questions that i've been doing in my workbook in my worksheets in all of the practice questions that have been given to me okay because textbooks are often very convoluted right there's so many words and half of it is honestly useless okay so it's good to consolidate the important information so that a few days before your exam okay you have everything you need to know for your papers okay and the second one will be practicing questions now i think it's easy for us to think oh i understand this concept right but sometimes it's only when we do a practice question in our worksheets in our school papers then we realize oh actually i didn't really understand what was required of this question okay so it is important to have exposure to more questions okay and that includes doing your worksheets doing your corrections okay and hopefully if you have time doing more school papers okay and the third one will be um good answering techniques okay so this is especially important for your biology topics okay so we will explore that a little bit more when i'm talking about ecosystems okay but keywords are very very important so if i tell you later okay this is important then hopefully you will take take it down in your notes in your like textbook or something okay and remember in your exams to write down these keywords okay so let's get started uh i will be using my ipad so just give me a second if at any point in time my screen starts hanging right okay please do let me know okay because this happens quite often now i will be using the curated notes to talk about these topics okay so also for you to like you know look through like oh okay do i want to like get these notes as well okay so if you are kid uh you can always check out our website okay for how to order these notes right so i'm gonna start with forces okay so i think you guys should already be aware at this point okay on what is a force and what the basic effects of forces are okay starting an object stopping okay changing the speed direction as well as size and shape do you need to memorize this the answer is no okay questions don't normally ask you like okay maybe the six effects of forces okay but this okay serves as the foundation for you to understand what a force is okay what do you need to know you need to know the instruments okay that can be used to measure forces that would be spring balance okay as well as the s-i units for forces forces are always measured in newtons okay and then we can have um three types of forces okay we split them into contact forces and non-contact forces so one of it okay which is friction okay is only exerted when two surfaces are in contact which is why it's called a contact force okay and in contrast we have non-contact forces such as magnetism and gravity okay so these forces exist even when surfaces are not touching each other okay so as i mentioned before right okay forces are always measured in newtons so keep that in mind okay because that will be pretty important when we're talking about gravity okay so under friction oh no it's already hanging okay give me a second okay so we're gonna talk about first type of force which is friction so friction is present whenever one surface rubs against any other surface okay but how much friction is present is dependent on texture so the rough on the surface there is more friction okay so what is important you have to know that friction always causes objects to heat up okay it never makes things colder okay when you rub your hands together for long enough oh my palms are so hot okay or you walk a marathon and then you touch the bottom of your shoe okay it's very very hot okay so friction always causes surfaces to heat up which also means that heat energy is being produced okay so this is a relevant concept when you are talking about conservation of energy which is something i talk about later okay heat energy is produced in the presence of friction okay what else do we need to know friction always slows down the motion of an object if you roll a ball the ball will eventually stop moving okay because the motion is being slowed down by friction okay as well as the fact that friction always opposes the movement of an object so if i am pushing a box this way okay friction is being exerted this way okay it always opposes the movement of an object okay so similarly sr unit for friction since it is a force will be in newtons okay so applications of friction nuisances are friction and ways to reduce friction i think these are in your textbook okay it's good to remember at least one example each okay now the second one and the most important of the three will be gravity so what is gravity okay essentially it is the force okay that pulls objects towards the earth okay and gravity causes objects to have weight so you can think of weight okay as the measure of force of gravity okay or it is a measure of gravitational force so what is important to take note of okay it is super important to remember the formula for weight okay weight equals to mass times gravitational force super important okay they don't give this to you in your like exams okay they expect you to already know okay how to calculate weight okay and on earth whether or not your question specifies it it your gravitational force is always 10 the value is 10. so for example i say oh okay i weigh 50 kg right okay but actually that term is wrong okay my mass is 50 kg okay 50 kg then i say what is my weight okay so my weight equals to 50 kg times 10 equals to 500 newtons my weight is 500 newtons on earth okay but of course sometimes questions will be like oh this person is standing on planet x this person is standing on the moon standing on jupiter okay then the gravitational force value will be different okay so you have to follow the question of when it's on a different planet okay but if it's on earth always remember that the gravitational force is tense okay so what else is important to know okay you need to know the differences between mass and weight okay i know we always use the terms interchangeably okay but they actually refer to very different things okay now mass refers to the amount of matter in an object okay the number of particles in an object okay so whether or not okay let's say this box has like six particles okay now whether or not you put this box on earth you put this box in space you put you put this box on like the moon okay it still has this six particles the mass does not change okay but weight on the other hand is the force of gravity exerted on an object okay is dependent on the gravitational force okay and gravitational force changes depending on location gravitational force on earth is different from the moon which is different from jupiter which is different from saturn okay so weight changes depending on where you are but mass never changes okay so this is a very key concept all right of course the measuring tools that we use will be different as well and the si unit will also be different okay so take note of these differences now uh next one will be magnetism this is generally a small thing i don't think there's much to talk about because you've also learned this in primary school okay so like post repel unlike pose attract all right um nothing much to be said about this okay now we go into pressure all right so pressure refers to the amount of force acting on a unit area okay so once again super important to remember the formula okay pressure equals to force over area now i always tell my students okay when you are doing a pressure question it is super important okay first of all to write out the formula so i want them to write down the paper pressure equals the force over area as well as the units so newton over meter square why because a lot of questions for example they'll be like oh i have a box okay 5 cm by 10 cm okay then what's the pressure exerted okay if you have a box 5cm by 10cm okay if you don't write these units okay you will just use the formula with like cm square okay and that does not work okay when you are using this formula you must be having meter square so it means that you have to be converting this cm into meters first okay so uh when you are doing these questions okay write down in your paper like pressure equals to force in newtons over area in meter square okay just to remind yourself what the correct units are okay uh yes okay then under oh no it's hanging again sorry guys this happens all the time okay so i want to go straight into energy energy is the ability to do work okay we are no longer talking about forces okay so energy the s-i unit will be in joules okay not in newtons okay newtons will only be for forces but for energy it will be in joules okay and there are different forms of energy okay so um honestly only the first four are important uh okay so it's the ones that i really need you guys to remember for your exams okay the first one would be kinetic energy okay and it's defined as the energy that object possesses due to its motion okay big words but essentially you just need to remember moving objects okay have kinetic energy when you're riding a bike when you're running a 2.4 okay as long as something is moving okay it has kinetic energy okay and the faster it moves the more kinetic energy it has okay so that's the first one you guys need to be very familiar with okay second one gravitational potential energy okay defined as energy starting in an object due to its positions okay once again very big words but essentially it is just okay energy when there is height okay so kinetic energy when things are moving but gravitational potential energy is when things have height okay so when you're standing on a cliff when you're standing on the 20th story of your hdb flat okay or you're just standing on a flight of stairs okay as long as you are above ground level okay that object has gravitational potential energy and the higher you go the more gpe you have okay so do take note of that now the third one is elastic potential energy so energy is on an object due to its condition once again uh doesn't really explain it okay so what is it exactly it is the energy okay that elastic materials contain okay when it is stretched or compressed okay what do i mean okay only things that can be stretched or compressed like rubber bands springs okay can have elastic potential energy okay but let's say i just have a rubber band right the thing i tie my hair with okay i just put it on a table like this okay we cannot say that there is elastic potential energy i must be stretching it or compressing it okay so there must be an action you must be stretching the rubber band or compressing the spring okay for there to be elastic potential energies okay the last important one will be chemical potential energy so this is just energy stored in foods and chemical substances so whenever you see questions talking about food or digestion for example okay a person eating an apple or you are burning fossil fuels okay all of this is releasing chemical potential energy okay and sorry my screen is hanging again okay winner okay so uh we can classify sources of energy into renewable and non-renewable sources so renewable energy is whatever can be replenished in a short period of time now okay and non-renewable sources of energy cannot be replenished in a short period of time okay so under renewable er okay there's four important sources solar wind water biomass okay i'm pretty sure this is all in your textbook okay so this is an example of like consolidating information okay not is to put like formula putting information like in a table so i can compare it okay all the information is just in one table instead of like three pages of my textbook okay so be smart about how you create your notes now uh it is important to also know the advantages and disadvantages of your sources of energy okay so advantages of renewable sources okay they are available indefinitely okay which means that you can never run out of renewable sources of energy okay there will be wind forever okay like it's impossible not to have wind right okay and it does not contribute to like air pollution okay but of course the disadvantage would be that it cannot be harvested all the time for example if today is damn hot okay there's no wind then how is my window gonna work right i'm gonna have i'm only gonna be able to harvest very little amount of energy that day okay then for non-renewable sources okay guys if you guys know how to fix this screen hanging thing please let me know we are okay non-renewable sources that would be your fossil fuels okay coal natural gas and oil okay uh as i mentioned before fossil fuels contain chemical potential energy that is released when you burn it okay so just recall our fossil fuels are related to chemical potential energy okay so advantages abundant affordable super cheap everywhere okay but they contribute to air pollution and they will run out one day okay now we are on to almost the end of this topic already what is the law of conservation of energy okay it states that energy cannot be created or destroyed only converted from one form to another this definition is super important so i need you guys to memorize the definition of this law okay why because um they do test this in your exams okay so just remember wholesale what is the law of conservation of energy okay but what does it mean hey it means that the total amount of energy is always the same okay you can't create energy you can't destroy energy you can only convert it okay from one form to another for example from ke to your gpe okay but i can't just destroy energy all right so a very common example of like um energy transformation or this law of conservation of energy will be like oh when they roll a ball or when there's something that's like swinging okay and normally they are talking about ke gpe conversion okay so you guys must be very aware of how this works okay i also think this is your textbook but just know that this is a very common exam question okay so you guys must be able to tell me or tell your teachers okay how this works how like which is being converted to what okay and why all right okay and the very last thing for this topic will be work okay work is just a transfer of energy okay and since it's related to energy our sr unit will be in joules okay now uh work is has certain conditions that need to be met in order for us to say okay work was done okay there must be a force acting on it the object must move and the object must move in the direction of the force this is very important let's say i have a wall here right okay and i'm putting a box next to the wall okay and i'm pushing the box against the wall i push super super hot okay i think i'm sweating okay then i'm like okay since i exerted so much force there must have been work done right okay but no no work was done why because the object did not move i was pushing a box against the wall okay and therefore the box did not move okay so the conditions for work you guys also must memorize it okay in order to identify whether or not work was done okay and of course the formula for work you guys also must be aware which is force times distance okay and distance measured in meters so if i have cm you have km you better convert it into meters ah all right okay so that wraps it up for the topic of forces i'm gonna share my screen again okay because it's hanging okay so we're going straight into our second topic which is heat okay now um for the topping of heat we can split it into general concepts okay general concepts of heat as well as our heat transfer methods okay so that will be our conduction convection and radiation okay so i want to touch on the general concepts first okay so by now you guys should know expansion is just the increase in size of objects when they are heated and contraction is the decrease in size of objects when they are cooled okay one thing to note is that the mass okay regardless of whether you expand or contract always remains constant okay the number of particles is always the same okay it's just that the space between the particles have changed okay so once again si units are always important okay temperature is measured in kelvin okay not degree celsius okay and then we can use a thermometer so this is a very common uh experiment okay that is tested for like mcqs okay and sometimes also even open-ended questions now you guys have probably done this in primary school okay where you hit the ball or whatever that you cannot like pass through the ring okay so you guys must be aware of how to explain it okay so what is going on okay the ball is getting hit and moving faster okay the particles are gaining heat and moving faster okay causing them to move further apart and increase the space that we occupy okay so the ball has extended the size has increased okay and therefore it is now too wide to fit through the ring okay so for these kind of questions you must relate it to the particles okay you must tell me that they move further apart and increase the space they occupy causing them to increase in size okay so these are examples of keywords that i'm looking for okay for you to score in your examinations okay next we are going to talk about bi-metallic strips so this is very important okay i know a lot of students get very confused about biometallic strips okay um i think as a student i never understood it even after i graduated from secondary school but as in now that i think back about it it's not that complicated okay because there is like cheap methods okay so first of all we need to know what a biometallic strip is okay it is just made up of two different metal strips that's the first thing you need to understand about these okay it's made out of two different metal strips and they always give you brass and something okay so brass steel or maybe they give you brass iron okay these are the very two common examples of bimetallic strips okay so how does it work okay you need to know that biometallic strips are often okay used in electrical appliances okay so look here on the application okay it's used in electrical appliances and it is used to connect or disconnect the supply of electricity so it's meant to open or close a circuit okay so these are basic electricity concepts okay and of course you guys also need to know some common examples of where biometallic strips are used okay fire alarms ovens irons thermostats okay but i want to go back to figuring out how these strips work okay so during heating uh okay brass always expands faster and more than the other metal okay whether or not you have the brass steel or the brass iron stripper okay brass is the one that expands faster okay so there's something that you guys should be writing down in your notes okay uh it's a heck matter so brass always expands faster okay therefore the length of the bra strip is longer okay than the steel strip and this causes it to bend okay someone asks why does brass expand faster okay so i think in upper secondary you will learn about this thing called thermal conductivity okay so this is just like a property of these metals for example properties like oh melting point boiling points okay and it just so happens that brass as a metal okay has a higher thermal conductivity which means that for the same amount of heat that you're supplying it okay both of them above a bunsen burner at the same distance the same height or whatever okay brass will always just expand faster okay so obviously because i'm not i hate physics okay so i cannot really tell you like super in detail why this is so okay but i just need to know that for a material like brass okay it always just expands faster okay so um back to the heating so the length of the brass strip will be longer than the other strip okay causing it to bend away from the brush strip okay because this is longer by skills together now okay it cannot you cannot just separate what okay so no choice it will bend away from the brass strip okay so when you guys are doing a biometallic strip questions right okay observe whether or not okay um is it opening the circuit is it closing the circuit okay and why so you need to tell me why okay so is there a tip on how do we know like whether the biometrics should bend upwards or downwards okay so very good question so let me shut my screen again because it's hanging okay wait actually super easy okay all you need to do right okay uh okay so right let's take a look at this diagram here okay the first thing you guys need to remember is that brass is the one that expands faster okay so brass will become longer than the other strip okay so obviously i don't really have two strips for you to like like visualize for you guys okay but think about it if there is a strip that just became longer but it's like fused to another strip what's gonna happen okay it's going to bend away from itself okay so if you look at this photo here okay we know that brass is the purple color one okay and still is the gray color one okay so it's going to bend away from the brass okay or towards the steel okay when we're talking about heating all right so it doesn't matter okay which direction so for example if i draw it like this okay it's always bending away from the brass so it means this one has to be brass okay that's how you remember then this one will be like steel or iron okay so you can write your notes oh it bends away from brass or it bends towards the other metal okay so um very good question because they love to test this like four circuits okay where they want to break a circuit so for example if i have my contact point here right okay i have my bi-metallic strip correct made out of two different metals okay then after they say oh after heating what happens okay uh the strip bends like this okay it bends like this then they say okay which one is brass which one is steel okay then how do we know the answer oh my gosh it's hanging again okay veda sorry guys okay see this one huh okay so this is before heating this is after heating you can see that it uh disconnected okay from the contact point okay then the question asks you okay which one is the brass strip okay youtube cr is bending away from brass okay so it means that okay we see that it's bending this way correct it bends upwards okay so it means that this one has to be brass okay it's bending away from brass okay that's how you identify which is the brass strip okay and once you get that then you will know that the other one is under metalla okay uh yes all right then of course it would be good to also remember some um common examples of expansion and contraction in daily life now i want to talk about heat transfer methods okay so heat always transfers or flows from a region of higher temperature to a region of lower temperature and there's three ways in which heat can flow okay conduction convection and radiation so conduction is the transfer of heat raw material without the movement of the medium so that's something that is very important to take note of the medium does not move in conduction okay if i hit a metal stick the stick is not gonna start flying off okay the stick is just gonna stay where it is okay but what is the concept of conduction okay before that i want to highlight that conduction can okay take place in all three states okay solid liquids and gases can can is can okay but it is very inefficient in liquids and gases it's so poor in liquids and gases that we honestly don't even think about it okay so from conduction we always just think about solids okay but it can take place in all three states all right so now i go into the concept so we look at this photo here where we are heating this methyl rod okay so what is happening okay the metal atoms are gaining energy from the flame okay causing it to vibrate faster and then these excited atoms will hit neighboring atoms and transfer their thermal energy via conduction okay causing them to vibrate too okay so for example i'm super excited that if i have that i hit my friend and now my friend is so excited okay so there must be contact between the atoms okay which is why it is effective in solids because if you recall your second one topic solid particles are very closely packed okay so if one of them gets excited it's so easy to okay hit neighboring atoms okay and it transfers very efficiently and fast okay so someone says so conduction can't happen through air hello i just say right conduction can take place in all three states so it can take place in air it can take place in water but it is just very poor okay liquids and gases are poor conductors okay so take note it can take place in all three states it is just very poor in liquids and gases okay so if you look down here in this table okay i've separated good conductors and poor conductors okay so good conductors will be stuff like metals okay common sense all right and poor conductors we have liquids gases as well as some solids okay like your insulators like your wood your plastic and your glass okay someone says my scientists say conduction can occur in metals much faster because of three electrons uh yes but this is not part of your syllabus okay so all you really need to remember and know is that okay metals is just really good as a conductor okay and you guys should also know that right okay very good okay so uh now we go into our second one which is convection okay so convection is transfer of heat via movement of the medium okay so that's important to take note of there's a key difference between conduction and convection okay convection the medium has to move which means okay it cannot take place in solids it is not poor in solids it's not like conduction where it's poor in liquids and gases it like physically can't take place in solids okay it will never ever take place in solids convection only takes place in liquids and gases why because your um your solid can't move now okay the particles in your solids can't move okay like i said if i'm heating my metal stick my metal stick is not gonna start moving okay but air can flow water can flow okay that is what i mean by the medium moving okay so you guys must be aware of how convection currents work okay so i'm just gonna go through very briefly for liquids okay so for example if i'm having a heat source here what is going on okay i am heating the water above that heat source so at that part the water molecules move faster and spread further apart causing the volume to increase and therefore its density decreases so i do i always tell my students convection currents are always related to density okay so if i don't see anything about density in your answers right you can forget about getting full marks for your question okay you must reference density because that's how okay convection currents work okay it is what allows things to float and sink okay so you must tell me that the density of something changes okay so now we know that the hot water density decreases so it will rise okay and then the cooler denser water will sink okay and therefore we've set up a current okay so someone's asking about air conditioner so it's the same concept okay so if i have a room right why do i want to put my aircon at the top of the room okay look at your own house why is the economies at the top because when i cool the air here what happens when i cool things when i cool things it contracts correct that's our general concept it contracts and therefore the density increases so the cool air will sink okay the cool air has space to sink because it's at the top it will sink down okay and the hot air will rise okay so that's why it's effective the cooling element has to be on top and the heating element has to be below okay so these are the key things that you must take note of in your exams sorry vera so there's anything you want to take away from this whole convection thing i just mentioned it is that the cooling element is always on top and the heating element is always below okay that's all you really need to remember all right and you should also think about how you want to start answering your convection current questions okay because it's a very common question pipe now last one is radiation okay it is a transfer of heat without the need for a medium so it can take place in solids liquids gases as well as vacuums okay not the dyson vacuum cleaner i'm talking about vacuums in terms of a place with no particles so there is a place like space okay so very important if the question ever asks you oh how do we feel the heat from the sun how does the heat from the sun reach off it has to be radiation and radiation only okay because separating us and the sun is space okay and only radiation can take place in a vacuum which is space okay so you guys need to know okay what are good absorbers and radiator radiators of heat okay which is black endow surfaces okay and conversely poor absorbers invitators of heat are white and shiny surfaces okay so if you ever get confused just think if i'm going centosa tomorrow do i want to wear a black shirt or do i want to wear a white shirt to feel less hot of course white shirt right you wear black shirt you're probably going to get a heat stroke okay all right because why the black material absorbs the radiant heat so well okay and then you feel so hot inside it okay so uh now i'm gonna go into chemical changes all right does anyone need a break you guys can like do a raised hand function or something okay someone's asking what is the difference between ammeter radiator and conductor okay um all right so conductor as the name implies is only related to conduction as a heat transfer method okay so when you're talking about radiation don't ever use the word conductor okay oh this is a good conductor heat okay no we're only talking about conduction okay so that'll be when we're talking about like old solids or when we're trying to say oh air is a pro conductor heat okay we are talking about conduction now then we have emitter and radiator emitter is the same as radiator okay and this these are related to radiation radiation as a heat transfer method okay it just means giving out okay so we have good absorbers of radiant heat i take in that radiant heat and i have good emitters already radiant heat so i give out okay that median heat okay so these two terms emitter radiator i use interchangeably okay i give out the radiant heat so can radiation take place in a vacuum yes it is the only heat transfer method that takes place in a vacuum okay so vacuum only radiation takes place okay it is the only way that we are feeling heat from the sun okay we do not feel heat from the sun via conduction or convection okay the heat cannot pass through via these two methods it only pass through and reach us off via radiation okay so that's something to take note of all right so i'm gonna go into chemical changes now all right so okay hold on okay so chemical changes right first of all we want to separate or differentiate physical changes and chemical changes okay what's the difference a physical change is a change in which no new substance is formed okay nothing new is formed all right and they are temporary and can be reversed okay so just think of example okay i want to mix i want to get hot milo okay how am i going to get help i know okay i have my cup of warm water warm milk whatever okay and i have my milo powder okay i put my milo powder inside i get a cup of nice hot milo okay a lot of people think oh my gosh this confirm is chemical change no okay you have not created something new okay you've just made water with milo powder inside okay mixed together all right you've not created something new okay so this is an example of a physical change dissolving okay i dissolve my milo powder in my water that is a physical change okay another type of physical change will be changes in state so as well you see melting boiling freezing condensation all of these are physical changes when the ice cube melts that is a physical change not a chemical change okay you have not created something new it is still water okay it's just one it's hot water one i mean what is solid water one is liquid water okay all right so i'm gonna go into chemical changes now hold on guys sorry okay so chemical changes is just the opposite it is a change in which a new substance is formed okay and unfortunately they are very very difficult or impossible to reverse okay so depending on your school notes okay some teachers want to see the word impossible some say oh tell me very difficult okay so just follow whatever your school teacher says okay but if they don't specify you can just write impossible okay so um one very common example of chemical change will be rusting okay so i'm sure you guys have some pots and pans at home right where the sides are a bit rusted okay rusting is an example of a chemical change what is happening in rusting okay hold on it's hanging again okay so rusting right what is going on okay i have iron in my pots and pans okay this has reacted with oxygen in the air oxygen like in the moist air whatever okay and that's gonna create a new substance called iron oxide okay in layman term we call this rust okay so once i have rusted something rust has formed okay i can't just reverse it back into iron and oxygen i just can't okay if it's rust it's rust now okay i can only remove that rust okay i'm sure you guys have rust cleaners you use your soap and you scrape it away okay you have not reversed the reaction okay you have just removed the rust all of that iron that has been converted into iron oxide i'm sorry that's it okay it can't go back to what it once was all right so therefore chemical reactions are practically impossible to reverse okay so we always represent chemical reactions in a word equation okay so you must give me your reactants okay then you must show me that the reaction takes place with an arrow okay if there is a condition so for example heat or light you must write the condition above the arrow okay and then you form your product okay so someone's asking the difference between oxidation and combustion okay i'll come to that in a hot second all right so now there are main types of chemical changes i want to look at the definitions of these reactions so anything can be considered a decomposition reaction when one substance is broken down into two or more simpler substances okay so just take note they must always only start with one reactant okay as long as you see two or more reactants that's not a decomposition reaction okay only one reactant breaking down into two or more simpler substances now we have this thing called combination reactions is in a name combined okay as long as i combine reactants okay i can consider it a combination reaction okay now the third one combustion reaction how do we classify something as a combustion reaction okay something must combine with oxygen when it is heated so this is the key thing that a lot of people don't realize there must be an element of heat okay you must have like a bunsen burner you must have a like a stove or whatever a candle okay there must be an element of heat for something to be considered a combustion reaction okay and the last one is oxidation this one is just adding oxygen you don't need heat okay you don't need heat for something to be considered oxidation okay so i'm gonna go back and look at this uh reaction of rusting okay iron plus oxygen gives me iron oxide how can i classify this reaction is it decomposition no why because i have two reactants i say decomposition can only have one reactant so this is not a decomposition reaction is this a combination reaction yes i have combined two reactants together okay so yes it is combination now is it a combustion reaction no it is not a combustion reaction why there is oxygen that's added but was that heat no there was no heat okay you can go play ground and you see the the railings are it's also rusted okay so i go put a candle there and you wouldn't like melted or something okay rusting happens all the time anytime anywhere okay you don't hit it for resting to take place okay combustion can only be considered a combustion reaction when you hit it okay so it is not a combustion reaction but is rusting oxidation reaction yes it is an oxidation reaction because you have added oxygen does that make more sense now okay so someone's asking about synthesis single and double displacement um boy i think uh uh what is that okay answers obviously no okay unless your school is like testing really really wet stuff okay like for example if you're an ip program okay i cannot help you also because i don't know ipc bus all right and someone else so the rest of the heat transfer method no need heat like combustion huh i just said combustion right you must have heat okay for something to be considered a combustion reaction you must heat it okay you must be like oh i put the bunsen burner flame at the thing okay yes i'll talk about thermal decomposition in a while okay so these are just the main types of chemical reactions okay so these are just broad categories okay so i hope you guys are also aware of how to like what the test for guesses are okay and how to answer them okay so you must have the appropriate keywords i'm sure your school has given you notes on this okay but i'm telling you that tests for guesses are super important not just now but also for your levels okay so do remember it okay now uh i'm going into this thing called uh reactions caused by heat so these two reactions thermal decomposition and combustion involve heating okay there must be an element of heating involved okay so thermal decomposition is when one substance breaks into two or more simpler substances okay but in the presence of heat okay so it is just like a subset of decomposition decomposition maybe you don't need heat but for thermal decomposition okay must have heat all right so for example um you can thermal decompose sugar okay or okay when you heat a carbonate okay so when you heat a carbonate you form an oxide and carbon dioxide guess okay then for combustion as i've mentioned before you combine with oxygen in the presence of heat okay so yes uh if you guys want all these tables then you guys can consider buying the notes okay yes so uh this one is also self-explanatory okay now reactions caused by light photosynthesis like photography for this you guys must be aware of the word equation okay so please remember your word equations okay and last one is electrolysis not very important for this topic okay you will be um learning more in depth about it in your electrical systems topic okay so far i don't think i've ever seen a question has like this in chemical changes okay so yes um i'm going to the last part already of this topic which is on acid and alkalis okay so first of all you guys must be very aware of the properties of acids and alkalis okay must remember okay so uh if you're making all notes you guys better also may own people okay differentiating the properties of acids and alkalis okay but generally speaking acids are sour alkalis are soapy and bitter okay as well as plus the litmus test you guys must be aware all right then you also should know the three main reactions that involve acids so you have acid metal acid carbonate acid alkali okay what do you need to know okay you need to know what the products are so for example if you have an acid metal reaction you must know hydrogen and a salt are produced okay the key thing okay you must know hydrogen gas is produced okay why must you know this because the control will ask you test for gases okay so if you don't know that hydrogen is produced you will give me the wrong test for gas okay so similarly acid carbonate reactions carbon dioxide salt and water are produced okay must know and then acid alkali salt and water are produced okay so at this point if you're still like oh i didn't know this please go and revise that because this is like the most important part of your chemical changes topic already okay uh one last thing will be on indicators data let me reshare okay indicators so if i just give you a cup of dubious liquid okay we don't know whether it's acidic or alkaline right okay please don't go and taste it okay i know a lot of students like to write an oh taste it if they sour the acid please don't test it now okay you're gonna burn yourself all right so how do we tell we have to use indicators now of course limbus indicator is the most simple but this one just tells us whether it's acidic or alkaline okay but it does not tell us the ph value okay so the answer i always give an exam will be universal indicator you can't go wrong with it okay it is the most common type of indicator you can use okay but if you want to use universal indicator in your questionnaire you guys must memorize the color scale okay you must be able to tell me okay from ph3 to 4 it's orange color oh ph 12 to 14 will be violet color okay so if you guys are using this remember to remember your color scale okay so that's that for chemical changes all right so now i'm going to go into the very last topic for today and that will be interactions within ecosystems okay so essentially i'm just going to highlight you what the very important things to take note of for this topic first memorize your terms okay these four terms memorize the definition for me habitat population community ecosystem why mcq always tells you they'll give you something and say oh what is that example of a community what's the example of a population so if you don't know the definition you will get this wrong okay memorize these four terms okay now everything surrounding an organism is called an environment we split it into abiotic okay as well as biotic so a biotech is physical environment your light your temperature your water okay and biotic will be your organism's interactions with one another okay so i'll talk about it a little bit later all right so under adaptations um i feel like this is something you can also use a little bit of common sense okay but um normally they're split into two types okay structural as well as behavioral adaptations so structural adaptations are the features of an organism that help it to survive for example like i broke a porcupine fish having spikes right it just has spikes it's not behaving in a certain way it just has spikes okay and that deters predators okay but behavioral adaptations are how an organism behaves in order to survive for example clownfish hiding okay inside sea anatomy okay you can choose not to right but it decides okay i'm going to hide inside this c anatomy okay so that uh predators can't see me okay so structural is what it already has okay stripes uh spikes are okay whatever and behavioral is how it behaves in order to survive all right so uh abiotic factors uh yes you guys just need to know all the physical stuff like light temperature water air minerals all of these are considered abiotic factors okay nothing to do with the organisms themselves it's just what you see in nature okay just be aware then now we talk about biotic factors so these are interactions between organisms okay so there's four main types predator prey mutualism parasitism and commensalism okay so what are the differences predator prey relationships quite self-explanatory one animal is a predator one animal is a prey okay one will hunt the other for food okay so like for example if you have zebra and lion that is for sure predator prey okay because the lion hunts the zebra for food okay or maybe you have like rabbit owl okay you don't need to know all the interactions in the world okay just use some common sense okay that is predator prey relationship now the second one will be called mutualism okay this is where both organisms in that relationship benefit it's a healthy relationship okay we stand all right so for example um i don't have a picture here okay but uh for shark right sometimes they have like these small fishes that are following them around called femora fishes they have a mutualism relationship because okay the ramora fish will eat off the parasites on the shark okay the shark kind of bathed but okay right so how does it clean itself there are more fish will eat the parasites okay and in return the sharks like okay you help me i help you we are brothers okay the shark will protect the remora fish from other predators the shark will not eat the remora fish okay so you can see that both of them are benefiting in this relationship okay we call this neutralism then for parasitism that is when one benefits and the other is harmed okay one is like whoa i'm getting so much out of this and the other is like wow i'm suffering so bad it's a toxic relationship okay for example okay there are these um types of fungi called bracket fungus okay it grows on trees and what does it do it steals the nutrients from the trees it takes its water it takes its minerals okay and it gives back nothing in return so this bracket fungus is benefiting okay if i'm reaching off it's like freeloading okay but um okay the tree is literally getting harmed okay it's like oh you're stealing all my water or my minerals okay someone says um my assessment book states there are more fish is commensalism um i think for this you better clarify the future okay because i'm pretty sure it's a neutralism relationship all right but for these kind of things really just go and clarify the teachers before your exams okay then someone says what's the difference between predator prey and parasitism okay so as long as there's an element of one animal eating the other animal okay there must be an element of killing and consuming okay uh like a and b right if a kills and eats b that is predator prey but if there is like a and b where a benefits and b is harmed okay but not related to eating beer it's just that one benefits and the other is harm that is parasitism does it make more sense okay predator prey must have an element of one eating the other for food okay then the last one is commensalism all right so this is where one benefits the other neither harm or benefits okay so if you're gonna grow three frogs huh very cute okay all it does is hide under trees okay for shelter so it benefits because it has free shelter but it doesn't harm the tree okay it doesn't harm the plant okay it's not like the plant it's not like stealing nutrients from the plant or anything okay it's just hiding under the leaves okay so this one benefits the plants neither benefit nor is harm okay we call that commensalism all right so now we're going into energy flow so what do you need to know you need to know that the ultimate source of energy ultimate source of energy is always the sun okay we can get energy from eating other organisms but if you trace it all the way back everything comes from the sun why because okay the plants get the energy from the sun enters an ecosystem okay via photosynthesis and the plants take food for themselves okay and release like oxygen okay so um yes just take note it's always from the sun okay uh and we represent the flow of energy in ecosystem via food chains and food webs okay so food chains right is just like one linear relationship okay so it is just the sequence of the feeding relationship between organisms every level is called a trophic level okay so we can see here every organism in the food chain has a role to play okay it always starts off with a producer okay why is it called producer because they can produce their own food okay produce own food fire photosynthesis okay so you have green plants you have algae okay anything that can photosynthesize okay it's called a producer now then everything else that eats something else okay whether or not eat plant or eat anymore okay vegetarian or not okay you are considered a consumer okay so from trophic level two and up you guys are considered consumers all right um how do we identify primary secondary tertiary it is always in order okay the one that feeds on the producer is called the primary consumer the one that feeds on the adult the one that feeds on the primary consumer is called the secondary consumer and the one that feeds on the secondary consumer is called tertiary consumer we will never start with all the answering then secondary and primary noaa is always primary secondary then testing so when you're doing your questions trace first where is my producer then from there from producer you'll be primary secondary tertiary okay just trace up all right yes so one more thing no two more things you guys need to know what decomposers are so they're organisms they feed on and break down their plants and animals into simpler substances that are returned to the environment now um for these examples i hope you guys check with the teachers because some textbooks say that earthworms are decomposers and some textbooks say that performs are scavengers follow your school notes okay if you google it i swear i google this and they say of homes are decomposers okay but follow your school notes okay but the two that i no for sure correct are bacteria and fungi okay must memorize examples okay so you guys also must know that decomposition produces carbon dioxide and minerals okay yeah that's the main thing you need to memorize okay decomposition produces carbon dioxide and minerals all right then with our okay and then we have another type of organisms or just organisms with a different role okay called scavengers now these are animals that feed on and break up big organisms into smaller pieces they are not decomposers okay they do not okay break things down into simpler substances like carbon dioxide and minerals okay they don't they just have a big chunk of meat and they break into smaller chunks of meat okay for example you have vouchers you have flies think of scavengers okay as very lazy animals they're like i don't want to hunt okay screw that no thanks okay i'm just going to wait for something to die that is a good thing okay so that's why you always see vouchers that will circle around dying animals right they're just waiting for it to die so you can have a feast okay or if you watch documentaries you will see that when like for example a lion dies okay then you see a lot of flies around the dead body okay these are scavengers okay so uh okay i will talk about photosynthesis and restoration later okay so listen to food chains and food webs first okay so i'm almost done already you guys need to know that from one trophic level to the next 90 percent of energy is lost that's a lot of energy being lost okay must know and you must know what they are lost as okay respiration defecation and even parts if i tell you to memorize memorize it okay because it will come up for your exams all right so example here okay if i have trophy level one grass with 10 000 kj of energy okay ninety percent of energy is lost so the grasshopper only gets one thousand then the frog only gets one hundred then the snake when he gets ten okay so i'm gonna backtrack a bit ah because someone asked about the the primary secondary touch everything so using this example let's try to figure out which is the primary secondary and tertiary consumer or what is a producer okay take note it always starts with a producer 100 percent of the time starts with a producer the next one will be the primary consumer then the secondary consumer and then the tertiary consumer super easy okay as long as you identify the producer everything else will be primary secondary tertiary consumers okay in that order all right okay uh yes okay so uh a lot of questions also ask you why do they have a maximum of four traffic levels okay because there's insufficient energy at the back of the food chain okay to support another consumer if at the snega level there's only 10 kj of energy how do we expect there to be another consumer why they're gonna they're not gonna have enough energy to survive okay yes kj is kilojoules okay uh yes all right so this one is not very important okay so now i want to talk about uh photosynthesis and respiration so this is the very last thing that i'm covering for today already okay so you guys must memorize the word equations for photosynthesis and respiration okay it is definitely on textbook so go and write it up in your notes very important okay so photosynthesis is the process by which green plants use black energy to make food okay green plants don't eat like us okay they don't like go to essence for mew or whatever okay they need food via okay photosynthesis that's how they make their own food okay meanwhile respiration is the process by which living organisms break down food okay specifically glucose but you don't need to know what that is now breaking down food to release energy what is the energy for it is for any sort of process the fact i'm speaking to you now okay i need energy when i drink water i need energy when i blink when i swallow all of these processes when i walk anything i do needs energy okay where do i get the energy from respiration okay all right so please go and um make your own table on the differences between photosynthesis and respiration okay very important because they love to test that okay so someone's asking do you feel more food you eat grass rather than me okay that's a very good question so i literally just googled this a while back because i had the same question as you as a student like oh does this mean um we should just be all eating grass because like then you'll be getting the most amount of energy right like there's not a 90 percent loss 90 percent lost 90 percent lost things okay so it's a lot more complicated than that because okay um so from what i get from google okay so uh is this is just a theoretical explanation on the flow of energy okay but how we like feel energized or like how we make or release energy through processes like respiration okay it's not just purely about the energy in the food we eat okay we also need stuff like vitamins minerals and sometimes these things are only present in meat okay and another thing because i think humans are naturally omnivores right okay so our digestive system is suited for both meat and plants okay so if you just have a purely plant diet okay that doesn't necessarily mean that your body is better at okay breaking down those substances than if you eat both meat and plants okay but it is quite a complicated scenario but for the sake of your learning in ecosystems okay all you need to know is that from one trophic level to the next 90 of energy is lost okay all right so please remember your word equations for photosynthesis and respiration okay so yes i'm literally running out of time okay why because now we're gonna have something exciting we're gonna have a kahoot quiz okay and that's the thing that uh you guys can win your notes giveaway from okay so let me figure out how to make this cahoot quiz live okay guys i think i got it give me a second do you want a sound either did this sound okay right but you guys have to deal with it then kenzie right can y'all please join it now so these will be common mcq questions that are literally taken from school papers okay so it will be a good revision for you guys as well i will wait 30 more seconds and i'll start [Music] do [Music] is everybody in does anyone need more time give me like a raised hand or emoji or something if not i'll start in 10 seconds oh wow everybody's in okay great okay let's start okay so you just it would just be a series of mtu questions all right and then i will uh yeah go through each question okay so let's start do okay yes great 22 of you guys got this uh question correct very good okay wait can i how do i how do i wait wait a minute wait can i review this question how do i do that okay never mind we finish this whole thing first okay oh guys i figured out how to review okay let me just review it on the spot right now okay now i'll go back to review the the other two questions okay so what is the most appropriate method to confirm if a liquid is acidic okay so majority of you all got it correct okay but some of you all still say it makes a liquid with an alkali now it is true that an acid will react with an alkali but we may not be able to physically see a change okay we know that a reaction has taken place but what if the s and alkali are both like colorless right then how do we know exactly that the reaction has taken place okay so the most appropriate method right will still be to use the litmus test okay why because all acidic substances okay we'll turn the blue limous paper red okay so very good most of you understood that okay so burning of fossil fuels is a chemical change why are the rest wrong why are they considered physical changes recall there's only two main types of physical changes you guys need to remember okay dissolving and changes in state dissolving salt and water you have not created a new substance you have just created salty water or salt water okay dissolving is always a physical change okay melting evaporation all these are changes in state okay you are just changing the state from one to another you are not creating a new substance okay very good now last question okay you see i told you i took all these questions from exam papers right okay so i already mentioned you guys must memorize your four terms habitat population community ecosystem okay because these kinds of questions are so common in your exams all right so if you had memorized it you will know that a community okay is defined as different populations living in the same habitat so different groups of animals a group of elephants a group of lions a group of zebras okay all living in the african savanna okay that is what i consider a community all right everything else i'm not considered communities okay very good the winner gets a note okay so hold on i need to screenshot this okay very good joy uh yes later i'll contact you okay or you contact me okay um so you do win like creative notes okay and for everyone else thank you so much for participating i still need to go through the first two questions all right i'll give you a second uh uh how do i do this sorry i'm a ted mook wait how do i do this okay okay okay so this question says an astronaut travels from earth to outer space how does his weight and mass change recall uh first of all mass never changes wherever you are so mass always remains the same and we just use elimination method you already know the answer is b okay but why does the weight drop to zero okay because the gravitational field strength of space okay is zero okay so anything times zero is zero so weight which is mass times g if j zero your weight will be zero okay you are weakness in space all right then for the second question what can be done to make the ball go through the ring so now the ball is too fat to go through the ring how can we let it go through the ring we have to hit the ring only so that the ring will expand okay so the ring becomes wider such that the ball can go through okay if we hit both of them nothing's gonna change okay both of them are just gonna expand then it still can't fit through okay but this the quiz was well done okay so i'm glad all of you generally have your basic concepts down okay so what's gonna happen now i am um wait i still need to share some sites with you guys okay but if you or generally need to leave or anything yeah just go ahead okay um i'm just wrapping things up already i'm not covering my content okay so yes i have to fulfill my applications as powerful mark so uh yes if you guys want to get the notes okay you can scan this to our code or just go to the website okay and it's made by yours to me okay so yes um yeah okay then uh for those who are keen on joining my group tuition okay you can also scan this qr code or you can also sign up directly by the website okay or you can just telegram me okay but do take note i'm not having any lessons for the month of may until like the second half of june because i'm not crazy enough to have lessons in the middle of your media examinations okay i want you guys to have time to study for your other papers as well okay so even if you sign up i will only contact you sometime in june okay for your for like joining in term tree okay yes what else okay yeah this one okay last one if you've enjoyed today's session and you feel that okay i've learned something i think it was good whatever okay you can always feel generous and help leave us a kind google review okay all right that's about it actually okay yes i have nothing else to say does anyone have any questions i'll take like three questions okay whether or not it's like science related little not-size related if not i would just end the zoom okay i'll wait like one minute and if you want to leave you can start leaving okay don't dicey one says how old am i oh i'm 21 okay i guess that's still like much older than you guys yeah but i'm not that old okay all right uh yes no problem i hope you guys are feeling more prepared for your exams okay i know exams are very stressful okay but it gets okay it doesn't get easier but you just get more used to like the stress of studying for exams okay no problem hope you guys enjoyed it yes no yes no okay uh at 7 20 i will end this so if there are more than four animals given during the exam how do you identify okay then primary tertiary primary secondary tertiary then quaternaria may the last one be the fourth okay all right uh and for joy okay joy do you have telegram can you okay so joy just telling me directly okay someone asked why is adaptation what what adaptation okay you just need to think is this a structural or is this a behavioral adaptation okay like what can help an animal survive what if he has different genes what do you mean polar bear grizzly bear well okay think about it polar bears are white correct okay so they blend in with the glaciers okay because it's always snowing in the in the arctic correct or the environment okay so if it's white is it a structural or a behavioral structural ma you cannot change its color white okay it's just white okay that helps it to blend in okay then grizzly bear cause it's brown all the trees the twigs the the the branches wait the trunks of the tree they're brown right so it's also a form of camouflaging that the greasy bear is brown in color okay it's also a structural adaptation can the top three winners win the notes unfortunately daryl says no i'm so sorry okay but thank you so much for participating um like they made to adapt to the increasing temperature of the climate uh sister i'm not a i'm not a biologist okay i i don't really know all the all the mating stuff okay can we get the notes you just shared unfortunately no because these are like the creator notes so they are like you have to buy it okay but if you are part of the telegram channel okay there are three notes so it's just a more condensed version of whatever i've shown on the screen today okay so if like you don't want to buy then you can just go and use a free note okay can can everybody everybody now end the call all right thanks so much for joining me on a saturday evening bye