I always well good morning everybody congratulations you got here on the second day you survived the parking lot right um I don't want to spend too much time on this so maybe just a couple minutes is there anything I can answer right now if you've been in the syllabus you've been looking your canvas is there anything yeah so for W plus you just get the fre Tri first and then use the once it expires then use codes or whatever and we'll talk a lot more about that tomorrow okay yeah but yeah you want to get into Wy plus and like enable the free right because you need to be in the book you need to be looking at the first homework assignment all that kind of stuff right I know those of you are on the wait list I can't add you till tomorrow right but um he'll have access after that and and the homework like is d Saturday however if you've had a science class like in high school or here like a chemistry class biology class you can probably do the chapter one homework it's it's unit conversions and some trigonometry I think right so um hopefully that's you know I often think that the real physics starts in chapter two any other things you read or saw worrying you you have to know figure it out right now tomorrow's a big day uh because we're going over a lot of the details okay about how the course works and things like that so don't miss tomorrow uh if you can possibly help me if you're going to miss tomorrow you got to email me right because we got to figure out uh how to get you the information uh all right so we did that let's let's just let's let's talk some science and some physics and some stuff today um you're going to notice that I'm not going to take roll today right again I'm going to do all of the ad drops and everything tomorrow um so don't panic because I'm not taking roll but my goal here is to do all of chapter one hopefully a lot of this is review and then get straight into chapter two uh because we need some time on chapter two so um what is what is this sck it's a meter stick okay and how do I know it's a meter thick well it's a meter long right it's not 36 in Long it's 39 and a/4 in Long right okay so this is a meter stick um and there are actually there's many different unit systems in existence however I boil it down to two there is the perfect unit system and then there's the dumb unit system all right so what makes the metric system so good well okay every unit system is pretty accurate and precise we can argue what those terms mean later I wonder where they came up with the idea of having everything divisible by 10 what do I mean by that right how many cm are there in 2.6 7 m 267 oh you did that kind of fast how did you do that so fast well centimet 100 and I move the decimal point over I'm done right so 2.67 M becomes 267 CM okay how many inches are there in 7.69 ft can't do that one so fast because multiplying by 12 isn't something we really practice right so the metric systems got that going for it let me share with you a um piece of information that maybe you didn't so how many countries use the metric system a a lot how many countries don't use the metric system and use the imperial system of units okay the answer is three okay right and we're the big gray thing over on the side right okay so yeah here's another secret here in the United States we actually use the metric system an inch is defined as 2.54 C our weights our lengths our volumes everything our quarts our ounces or whatevers right that's all defined by its metric equivalent so we are in fact using the metric system everywhere we go we just put some 12 in in a foot why oh what what what's you guys know do you guys know the original definition of the like yard it was like the distance from the king's nose to their outstretched left hand or something like that right basing a unit system on a person is not a good idea right especially royalty because then they in breed and weird things happen right and it's just it it's a disaster right so the metric system defines itself according to physical constants in the universe most of them having to do with the speed of light and I don't want to get into Metrology because it's just going to bore you and all that kind of stuff but you just need to know that the metric system is invariant meaning it doesn't change over distance and time and all that kind of stuff whereas any other unit system kind of does weird stuff okay why are we talking about unit systems well um units are really really important and we need to know like because there are because we live in the United States and because we have this sort of different unit system that everybody else in the world uses and by the way if you're going into any kind of medical field you're going to be using the metric system all the time if you're going into chemistry you're going to be using the metric system all the time if you're going into engineering they're done okay because for some reason engineers in the United States always use the impal system so this is why we're going to spend some time on it I mostly use the metric system in here uh but how do you uh give me give me a three-digit number uh 3.47 I heard 347 but we're going to do 3.47 okay we have 3.47 uh meters or feet feet okay and we want to find out what 3.47 m is what's the equivalent in feet right okay so how do we do that hey Siri what is 3.47 Ft in meters so I turned off her voice uh but she says 1.06 but that's how you do it right you just asked Google but what is Google or Siri or anything else doing well okay they round but but like how how do you what do you need to get from this to meters yeah we need it's called a conversion factor you're hitting it right okay so we can go look up the conversion factors and you're like well Mr B the computer can do you're not always going to have well actually you're going to always have the computer with you never mind um one foot is equal to 0.3048 M or and this is the kicker okay 1 meter is equal Al to 3281 ft which one do I use that's the correct answer but how do you know which one the answer is there's only one way to do it you always multiply now I'm kind of this is a trick okay but you're always going to multiply what do I mean by that you're going to multiply by a ratio you guys know that multiplication and division are really not different from each other right division is just multiplying by the inverse okay so that's that's kind of where I'm going here so if I have three I want to know how many meters that is I start with whoops I start with really bad handwriting is what I do where's my 3.47 feet and then I'm going to multiply and I make I make a big ratio here okay and with this ratio I'm going to let the units do the talking for me in other words I want to get rid of feet so where would I put feet numerator denominator to to get it rid of it goes in the denominator right it's upstairs right there I want it downstairs over here which means that meters is going to go on top and now which of those con verion factors do I use the answer is it doesn't matter the answer is you can use either and we're going to do both let me let me do 3.4 man my fours are having trouble today 3.47 feet we'll do another conversion factor over here feet goes in the bottom meters goes on the top so I could use the one foot equals 3048 mters where do I put the 3048 M top or bottom top the meters is in the top the number that's near the meters goes with it goes with it so that means I put the one foot on the bottom okay in the other example where do I put the 3.28 one on the bottom why because it's 3281 ft right for every meter okay everybody pay attention this is a line right here in the middle of class everybody on this side do the top one each calculator out everybody on this side do the bottom one let's see what we get okay this side of the room anybody got a number shout it out. 1.57 1.57 do somebody else get 1.57 yeah good all right 1.57 M okay this side of the room what' you get 1.05 right a little bit round off air Maybe cuz numbers are numbers right but the point is is that you're always just going to multiply right multiply by a ratio and make sure that you get the units upstairs or downstairs in the right spots and the conversion factor goes along with it this is how we teach the machines to do it for us and it's important to know where it comes from okay so what do we do is if um Let's do let's do this what do we do okay how do we find out how many seconds there are in one year we could ask Google right but let's let's do it by hand where do we start what do we know yes but what do we know we know it's one year right we're given that it's one year so that's where we're going to start okay so one year and now I'm going to multiply right and what am I going to put in the bottom a year and now I got to get to something a conversion factor that I might know in days maybe right I can't go Dr the seconds I can't do that number right but maybe I could go to days okay so so in one year how many days is that 365 and A4 okay because sleepier stuff right okay now that I'm at days notice I can just keep multiplying here right where did days go top or bottom those and bottom okay maybe we can go to hours right okay because we know that in one day there's 24 hours all right what goes on the bottom hours because I again what I'm going for here is the ability to have these things divide out from each other right okay and the year disappears so on and so forth okay uh in one hour there are okay well I'm a shortcut 30 my undo button go 3600 seconds so I was ging tired of writing stuff here right okay um it's 60 60 minutes in an hour and then 60 seconds in a minute and what's 60 * 60 3,600 okay right so anyway you don't have to S cut it like that but then in my calculator right I'm going to take 365.25 multiply it by 24 multiply by 300 3,000 I'll have I don't care what the answer is I don't just want to know right but my point here is that when you're converting units multiply right and and and be clever about top and bottom where the the different units go so that you can eliminate them right and I'm left what am I left with in unit wise that seconds right there right and that's what I wanted all right let's see yeah okay it's time for a quiz so uh what we're going to do for the next 15 minutes is I'm going to teach you how quizzes work in this class right right this quiz is more about learning how to do quizzes than it is about I mean the quiz question is kind of important it involves un surprise surprise uh let's see here what I want you to do is everybody take three of these sheets we're going to run out and some are going to have more so in the back just sort of send them sideways whatever way they need to go for people everybody gets three of these and you get EXT we got yeah there should be those of you gotx this more SE all right everybody got three all right um so uh is it working one second had to redo my tech uh this time with the recording stuff so it doesn't always work way it's supposed to there we go all right so don't forget to put your name on it okay I always make fun of doct Staff staff teaches a lot of classes on campus doesn't he or she right says no idea what the teacher is um okay so quizzes in here are not about points they are really about you teaching each other and so to that end quizzes almost always are going to come in pairs in other words there's going to be like for today quiz 1.1 chapter one first quiz okay and a quiz 1.2 they're going to have the same point value right so quiz 1.1 I don't remember what I said three points two points uh two points each okay so it's 1.1 two points right quiz 1.2 is also going to be two points all right got to put that on the board so I remember so what you're going to do okay is you're going to just in in the first box 1.1 out of two and in the second box 1.2 out of two I'll always sort of just say okay this is the quiz numbers and the points are you know the same between them okay and believe it or not the question for 1.1 and the question for 1.2 is going to be exactly the same question so why are you using two boxes I want you for the first quiz toy try it all by yourself I want you to try it all by yourself because you need to find out where you're having trouble whether or not you're getting this kind of thing and if you've ever been in a class where you've been listening you go oh wait and the teacher asks a question like oh wait I know and then the person right next to you blurts out the answer what happens to your like train of thought when that happen yeah like derails right like like and what you've been robbed of is a chance for your neurons to link that pathway through and connect pieces of information right and so what I want to give you is 30 seconds two minutes it depends on the quiz question how long I give you but I want you to try it first on your own right find out where you're at and then you are going to write down the answer in the box with hopefully some sort of explanation now a lot of the quizzes will be like multiple choice so you can just say I choose a or just write a and then give me a reason right this is a terrible reason okay just because I say something doesn't necess right there should be some argument mathematical physics whatever okay if you so side note you are going to keep these for the entire semester you're going to turn them in at the end of the semester okay so if you want a permanent record of everything is going on work the quizzes in your notes right and then you can put the cliff notes on here right your answer and a really short explanation okay um but I will gra I will take these at the end of the semester and you won't see them again okay so just just so you are aware of that right or or do it all the quiz sheets take pictures insert it into your iPad Notes whatever it is you want to do but do know that these will disappear at the end of the semester okay and so you're sitting there you've done it you've answered it right what's the second box for what I'm going to do is I'm call time and then I want you to turn to each other and tell each other what what your answer is but most importantly why why did you pick the one that you picked right and you can be honest you turn and say I I guess right and so you're going to start a back and forth and what you're doing there is teaching each other and you're going to find out what you know and what you don't know so the second box if you change your answer right if somebody teaches you something and you realized you missed something or whatever right you are going to write down the new answer and the new reason or maybe why you change right I forgot to consider the blah blah blah right okay this is made up there's a website for making stuff like but you're gonna if you change your answer you're going to write a there if you keep your answer the same just draw an arrow don't don't rewrite everything an arrow just connecting the boxes will tell me I'm keeping my answer the same right or just say I'm keeping my answer whatever right just indicate that you're not changing your answer this I call the group quiz you do not need to answer the same as the group this is still your individual answer it's just an answer that has come about because you had reflection in teaching and an opportunity to communicate and then we'll fight over what the real answer is and and then um you score it you grade yourself often the hardest grader in the room okay and you're like sweet I just got 50 points right 50 okay right I mean the points actually don't matter because I give out about 150 points worth of quizzes during this semester you only need 50 to get an A there's no extra credit soon as you get to 50 it just truncates okay so what usually happens is people are all like weaked out about the numbers for the first three weeks and then after that you get to the halfway point of the semester you're like I've got 50 points and by then you're like oh quizzes aren't really about points they're about about this opportunity to teach each other so with all that being said let's go through the first quiz right all right okay so here is your quiz question I'm going to put it up on the screen okay and then you're going to figure it out on your own I'm going to give you like 90 seconds okay I want you to tell me how many cubic cm there are in 1 cubic meter there are 100 c in one meter there's the conversion factor for you okay but I just want you to tell me how many cubic cm there are in one cubic meter come up here you about 30 more seconds okay this point hopefully you have something written down in that quiz 1.1 box it could be just the answer you could have done the work in your notes or something like that right so I know there's not a lot of room in that box but you want to have something written down and we're not going to change this answer now right this one's going to be set in stone any changes you make are going to go where second box right the 1.2 box so right now turn to each other tell them what answer you got and why [Music] go I'm sorry again need three [Music] so okay at this point write down any different answer you may have give a reason maybe for why you changed it if you didn't change it what are you going to do arrow down normally I won't tell you or you remind you to write down your answer hopefully as you're discussing things right you'll make the changes or maybe you'll just both agree and you just draw an arrow right okay but because I'm walking you through this I'll give you time right now just in 1 point2 if it's different different answer and then why it's the same drawn ER okay so let's figure out what the answer is and um we're going to uh we everybody knows that you figure out stuff by voting right and so to maintain the illusion of democracy I'll let you vote on the answer all right so how many of you say the answer is one 1 cubic cm per cubic meter no okay how many you say it's 10 how manyan you say it's a hundred okay few of you okay a thousand is anybody sensing a theme 10,000 100 why am I always going by 10 right uh what was I 100,000 a million oh anything more than a million okay so we saw two peaks in the voting populace okay one was at 100 and the other was at 1 million uh the 1 million Camp was in the majority so we'll make them defend their position first uh those of you that said 1 million what's your argument what are your thinking how'd you get to your answer so there is 100 C uh we could just basically C both of them we can c to get our units into Cube and then we would apply the CU also to to the number oh wait so if if I Cube this side I've got to cube everything yes and so that would make this a centimet cubed right but what's 100 cubed milon it's 1 million okay um anybody do it any different way yeah I I thought about um like the one okay so you kind of you kind of visualize yeah I apologize for my lack of artistic ability here okay right and you're like well 100 on that side 100 on that 100 right and to find the volume of something I go 100 time 100 * 100 million okay um this is a test of the state center Community College yeah you don't need to repeat yourself thank you for interrupting my lecture we were learning something all right so visualization mathematical okay um the way that I taught you to do units and multiplying stuff together right so we have uh we have one cubic meter right we start with one cubic meter right and then I multiply right and what do I put on the bottom meters what do I put on the top cenm what I put in the bottom one and up here I put 100 right okay now if I can I just cancel both of those no right that would only bring it down to squared wouldn't it okay so if I'm starting with a cubic meter I've got to do another one of these people that answered 1 million am I am I am I getting your kind of thought process here okay those of you that answered 100 where'd you go wrong on sides yeah cube root dude you're going for the hard stuff you probably didn't realize that like the conversion factor is without the cubes right and you can't just Cube the Cent met in the meter you got to cube everything or you got to do the conversion factor three times so you might be sitting there going oh my gosh I just totally screwed up I can't do no no no no no what do we do with mistakes learn we learn from them right so you want to write down in your notes okay I messed this quiz up I got to make sure to remember to check my units right make sure that don't make assumptions about conversion factors whatever whatever kind of mistake you made there learn from it it's awesome you actually you're actually in a better spot the people that got it right you learned something people that got it right are like I got it right okay so all right so now score yourself right if you answered say a 100 the first time and a million the second time you know zero and then two on the second one maybe you need some pity points today because you've had a rough day one out of right like you're scoring yourself right the points actually don't make anything okay you put points on things cuz otherwise students will ignore it doesn't have point right but the the idea here the the chief idea of any quiz is really to give you a chance to see where you're at and then give you a chance to teach each other and that's what I'm talking about like you interacting with each other generally we'll do one to three of these per lecture it really depends on the topic and what's going on how many questions you have and blah blah blah right so you can anticipate that bring your quiz sheets all the time I know they're annoying cuz their actual paper but you'll you you'll get it all right let's see we did all that um I should probably talk about this um so just real quick um this is something you're going to come across in Reading you're going to see it on YouTubes uh you're going to see I I'll talk about it every once in a while in physics we have uh we actually often don't care about what the actual answer is okay what we're more concerned about sometimes is like are we in the ballpark does the answer make sense and how do I know if it makes sense we do something called an order of magnitude calculation the way I like to um talk about this one is um give an example so let's say that we we invite a engineering major a physics major and an English major to measure the volume of this room okay so three students three Majors they got to measure the volume of the room um what does the English major do cries right they just cry okay because now we're measuring something and it's not in their ba okay what does the engineering student do I want the volume of air in this room what do you do oh okay so you get a measurement tool maybe this one okay right and uh how are we going to find the volume we got we got to measure the length oh and then we got to measure the right and we got so engineering student takes I need a laser right don't this is I need a laser right and then wait a second the room's not a cube so now I need an angle there's heads in the room I've got to subtract the volume of everything there's people in the room oh I know I know I know I know we'll fill the room with water we'll fill the room with water and then we'll measure the why are Engineers like that why are they like so precise and stressed because you can get sued right Bo you do it Boe okay you do it wrong right people's lives are on the line Engineers is where the rubber meets the roads where science goes into the public space right and so it's important that you get things right which is why I have an emphasis in this class of yeah let's get the right answer that's really when you've got that 100% right okay now the physics major Walts into the room probably very arrogant physics is the the cheap science of all science okay let's see here um it's about 10 m 10 m 3 m 300 Cub M what one what's the difference in approach between the engineer and the physicist it's like a Precision right the engineer wanted to know exactly the physicist wanted to know within an order of magnitude and that word order of magnitude means power of 10 so a physicist would be fine with knowing that this is on the order of hundreds of cubic meters it's not thousands it's not tens it's 300ish right so if I asked you how many Blades of grass are there in one acre of grass land you need to start making some assumptions okay kind of grass is prairie grass or is it like that putting green grass where all the blades are like really close together right you might take a measurement of say maybe one square foot in that prairie grass and count the number of blades right now is every square foot always going to have 131 Blades of grass no but you can get an idea for how many Blades of grass there are in an acre by taking a sample it's an order of magnitude it's not going to be exactly the number of Blades of grass right but it's going to be close how many piano tuners are there in New York how many hamburgers can you get out of a cow these kinds of questions vary depending on how big's the cow how many right what what cuts meat right but you can get an order of magnitude you can be within a power of 10 of what the actual answer is and often times that's really all you need to know so if you see in order of magnitude calculation or somebody mentioning that oh this answerers within tic that's what we're talking about we're saying it's it's in that range where we say yeah our assumptions are holding so I just wanted to pass that by you right make sure that you understood when I drop that language all right let's do chapter two let's get started that was chapter one okay so ideally between the book and me you now are able to do the questions in chapter one okay I might have lied I think the trig might come in chapter three all right let's um okay so chapter two is where physics really starts to happen okay it's um we're we're really going to start defining how things move and we use a series of um symbols ideas symbols represent ideas right we use these series of symbols in order to um talk about how something is moving so I want to talk average is instantaneous but let's let's back up because you probably haven't read chapter two yet you probably probably haven't even clicked on for quick here so I I'll be nice and and just sort of give you some information this this would be kind of thing I'd almost expect you to have read already and have these definitions down right so that I can talk about how to use that's where we want to spend most of our time um we'll back up okay so describing uh where something is how do we describe where something is in the universe right but in a more scientific sense we've got to be able to compare positions of things all kind of stuff so so what like in math what did you do to find a a point in space yeah there had to be some sort of reference a coordinate system of some kind right well let me tell you about a superpower that you now have because you are in this class you have the superpower of deciding where the center of the universe is you always knew it was you right okay that what I'm talking about is you hit the Picker zero it you got to start somewhere want to reference everything so um here hate okay right so I marked my zero point okay this is zero what's that way positive or negative positive what's that way what's that way positive up negative right we got sort of the standard cartisian coordinate system going on here right okay so now if I go one meter this way what would you say my position I is positive 1 meter once you get used to start thinking I know mathematicians told you what there's no plus inherent is implied no I didn't it positive one okay all right so if I'm here at zero and I go this way one meter now what is it negative one okay all right so now if I walk one two meters this way and then I walk one two three meters this way how far did I go had one two one two three that's five meters right the distance I traveled was five meters but my displacement my reference from where I started is what negative one is there a difference between distance traveled and the displacement of an object yes yes now can they be the same if I start here and I go ne1 how far did I go one meter I didn't go negative I traveled one meter right but my displacement is what if I start here and I go 2 m and I stop how far did I go 2 m what's my displacement positive so they can be the same but they don't have to be the same right displacement and distance traveled two different things two different ideas how do we represent symbolically how do we represent the location of where something is what symbol do we use hint cartisian coordinate systems X right X ARS the spot okay so okay do not do not okay just stop for a second I'm about to put some math on the screen okay symbolic math not numbers symbolic math you've been trained your brain has been trained into a pain response whenever math appears on the screen okay your brain is going to want to shut off and just start writing things in the hopes that somehow it gets seared in there at some point okay don't do that okay math math is bad but in this class it's a foreign language we use it to express ideas okay so please don't turn your brain off just because I'm going to go in and write down X right okay let me introduce you to another symbol okay and this is the one we're going to use to indicate that there's a difference between Where We Are versus our displacement right the displacement being a comparison between where we end and where we started that symbol is a Delta it's it's just a big triangle okay it's the Greek letter Delta and it literally means take the final position and subtract off the initial position in the case of a Delta X okay all right so I can indicate position just with X I can indicate display placement by saying this Delta this difference between where I start and where I end so like like if I'm here at zero and I end up at1 what's my final [Music] position1 right okay what's my initial position where' I start zero what's 1 minus 0 negative 1 right okay it works how how do I now figure out how fast I did it what's it called if we change our position in time that's velocity if we change our position in time what does delta T mean change in time change in time the zero time is always just zero right t zero okay but I could I could start here and do the tortoise 5 Seconds To Go 2 meters right okay my displacement is what two my time is five right 2 fths right unitwise what's the top unit meters what's the bottom unit second so a meter per second would be my unit for that velocity right or I could do the two meters in one second which one was faster second one right because I went two meters in 1 second and two is bigger than two fths right okay so a velocity is trying to indicate how fast something is moving uh uh what symbol are we going to use V wouldn't that be convenient oh well it turns out that that's exactly what we're going okay right we'll use the symbol V okay and uh physicists usually write that v as a kind of a curly script it's got some Wiggles on it you can write the D however you want all right so we got that idea okay then there's one more idea that we use to try and capture how something moves so we got position we got velocity what's the last one acceleration this is where everybody loses it okay what is acceleration I can do it symbolically okay it's going to be a change in velocity in time okay by the way my velocity has units of me/ second right so okay so let's see it's a change in velocity a change in time which means the units are going to be what what are the units of velocity it's a meter per second and then I'm dividing by a second so it's a meter per second per second which is diffic you don't want to say that all the time okay mathematically when you have a fraction divided by another fraction what have you put it together right so it's becomes me/ second squared and that's often what we say when we're talking about an acceleration Okay so we've got down sort of what these definitions are mathematically symbolically what they are but but what is an acceleration like conceptually no that's velocity a change in velocity it's a change in velocity if velocity is how fast you're going acceleration is how much your motion is changing so so if if I start here and I walk with the exactly the same velocity all the way across the room what's my acceleration it was Zero it was a constant but the constant was Zero what does zero acceleration mean no change in motion velocity velocity is motion I didn't change my motion okay but now if I come over here I start over here and I start slowly and I get faster and faster and faster and faster did my motion change yes okay that was changing motion my acceleration was positive or negative how'd you know okay all right all right starting here starting fast and then slowing down did it what direction was my displacement positive or negative positive we all agreed that I moved in the positive direction okay what direction was my velocity which way was I moving I was moving in the positive direction what direction was my acceleration my acceleration was negative I was moving positive but slowing down which means my motion was changing in the opposite direction to my motion are directions important yes absolutely in chapter three we're going to talk a lot about directions okay with this thing called a vector but for now we're going to base this and make sure that we're all on the same page right if I start here at zero and I speak heat up what direction is my motion my velocity positive what direction is my acceleration my change in motion also positive I sped up and in the same direction I'm going okay so now okay I am going to be my velocity will be Which Way negative okay and I am going to start fast and slow down right so I'm going to start at a Sprint and then SL slow down what direction was my velocity what direction was my acceleration how many times you going to make this mistake all the time okay you're going to start by making it all the time and you're going to figure out where your assumptions are wrong and correct and you're going to try and get all those mistakes out of your system question okay so a change in negative velocity yes okay everybody hear that wait a change in negative velocity all right I'm going fast and I'm slowing down what direction was I going negative but my change the way my velocity changed was pointed that way I was slowing down right if I'm going one way and slowing down my acceleration it has to be against it right if I throw a ball in the air okay after it leaves my hand what direction is its acceleration an entire education K through 12 and we're still confused about I don't blame you I blame your teachers okay what direction is the acceleration for a ball that's in the air what direction does gravity point right if the ball's going up is gravity pointing up no right the acceleration even if the ball is going up is pointed which way how do you know it's slowing down right it leaves my hand and slows down and then gets to its maximum point right which way is it moving up and it's slowing down so which way is the acceleration it down and then it gets to here right and then it starts coming down again right what direction is it now going down Down's velocity is down right and it's speeding up which ways the acceleration down get up gravity never changes its [Music] Direction no no the acceleration stays the same it points down at 9.8 me/ second Square we'll get it that in chapter four okay the point I'm trying to make is okay where are we messing up where are we messing up I thought I understood gravity before I came into this room let me tell you what's happening okay this is what's happening in your brain most classes you walk into okay you come in with your knowledge bucket okay and it's empty and you go into history class you go into philosophy class you go whatever right you come in you go fill my bucket okay and the teacher just goes right in physics you're coming in with your bucket and it's got however many years old you are of information of knowledge of things that you think you know and there's some dirty water in there okay there's some really dirty water in there for example why is the sky blue direct atmosphere yeah you're actually right it's the first time I've heard the right answer why do most people think the sky is blue the ocean blue what color is water we is transparent what color is the ocean on a cloudy day not blue it's gray right the ocean is blue cuz the sky is blue not the reason that the sky is blue is because something called ra scatter but you know what it is but no way else knows it right that's bad information okay so as what do I have to do in here I have to dump your buckets out I do and sometimes it's rough you're experiencing it right now right you're like negative one and half right yeah right slam it down go become an English ma right no right I have to correct misconceptions that you are just you're out to stop light okay light turns green you hit the the gas in the instant you hit the gas how fast are you going zero what's your acceleration not zero it can't be zero because in the next instant what will you be doing moving you've you are changing your motion so so what direction is the force on you when you hit the gas start accelerating forward which way are you pushed when you accelerate push back into the chair yeah right you hit the Gap it wrong there's only one direction you can be put if you are changing your Motion in the forward Direction the pushes forwards name the object that's pushing you backwards in your chair it's not an object no the car is pushing you which way forwards do you see what's wrong you don't understand the physic that's fine we're going to get to that in chapter five okay the point I'm trying to make is that you think you know what acceleration is you probably think acceleration velocity are basically the same thing and I don't have to worry about it do you need to worry about it yes my teacher's shouting there has to be something here and so together we are trying to throw out the dirty water and replace it with clean water that often comes on the form of golly you are really wrong let's figure out why it is excellent to be wrong in here like it really is good because that means we're identifying dirty water the hard part is getting that dirty water replaced with clean water okay quizzes the things we talk about together all of that is designed to get you really thinking about what's going on okay so back to back to this whole acceleration thing right and we'll just do the ball again okay when the ball is moving upward do you agree that the velocity changes direction does the velocity go up and then down we're good there everybody usually has a perfect concept of what that is okay now was the ball speeding up or slowing down in the first half of its flight it was slowing down so if it's moving up positive but slowing down what direction is its acceleration down negative right and then at the top it start it turns around stops right goes from positive velocity to negative velocity so now it has negative velocity but is it speeding up or slowing down it's speeding up so if it's moving down negative and it's speeding up what direction is it is it the acceleration it's also negative because it's getting faster right so something's changing its motion and getting faster the acceleration velocity you're point in the same direction if something is slowing down then its acceleration and velocity are pointed in opposite direction yes up going down meel no in the case of gravity acceleration always stays the same gravity accelerates all objects at the same rate and we'll find out in chap why in chapter 133 okay the acceleration of you throw a mouse or or a or a elephant off of the building which one hits the ground first they're supposed to hit at the same time now with air resistance we'll get to that later okay right but but Galileo discovered that gravity accelerates all objects the same rate not everything has the same force of gravity acting okay we're getting ahead of ourselves we're getting ahead of ourselves okay let's let's let's get out of the we and come back to what we're trying to do here okay which is taking this one step further because these Deltas they represent a period of time don't they okay so what's the difference between average and instantaneous okay this is a graph a plot of position versus time there several of these in the book go back go read how to read a position versus time graph but if a position is changing in time that would be represented by the a line like this okay and what's a change in position divided by a change in time a velocity so this line here represents a velocity right so this is a trip to Los Angeles right you get on the 41 what's the speed limit on the 41 okay this is a problem okay it's 65 not on the 99 right okay so from the 41 then you get on the 99 what's the speed limit on the 99 about 7,000 M hour right cuz if you're not going 7,000 M an hour at the Jensen inter change you're dead cuz the trucks are all going to run you over right okay why is this steeper for the 99 we are changing our position more in a shorter amount of time right now those of you that have calculist class okay you know you know what the slope of that line is what is it it's the velocity and we use a fill in the blank derivative there it is why is the 405 a straight line what's the velocity on the 405 any of you that ever been to La know that the 405 is La County's designation for its largest parking lot right because you get on the 405 and what is your speed zero like like you're not going anywhere people that get on the 405 pack survival gear because you're going to be there for a while right so that what's the velocity for a like perfectly horizontal line like that it's zero isn't it okay all right but now the Spectre of the derivative has reared its ugly head all right what okay I was going to ask what a derivative is I don't want to know but to scare you in the Limit Oh My Gosh as delta T and x and everything else goes to zero of this Delta X over delta T we say okay what are we doing there what are we trying to say that we're doing there so like like on the four on the on the is my speed on the 41 the same as my speed on the 99 no right but I can get an average speed for this trip let's say that it's a 200 M trip and it took me 4 hours what was my average speed for the trip 50 how'd you do that 200 miles divided by four hours right miles per hour is a velocity because it's a distance and a time it's just not the perfect unit system but it's the one we use okay fine 200 divided by by four is 50 so that's 200 that's 50 m an hour on were we going 50 mil an hour the whole time no okay because on the five you get to the grape vine and you discover how many people in the valley don't know how to drive in the mountains right and so on and so forth and my kids get sick and I got to pull the car over and hose the whole thing out just right your speed isn't the same all the time but what if I want to find my speed say between Gorman and Bakersfield which I always hope is like as short as possible anybody here from cor okay right there just nothing out there right if I shrink that time interval I get a more and more precise reading on what my velocity is and if I can shriek it down to the instant I'm measuring it like right now what is my velocity then I've got what's called an instantaneous measure in math speak we change the Deltas the capital triangle Deltas to what Little D's so a change in position an instantaneous change in position an instantaneous measure of position instead of being a Delta X would be a DX and a instantaneous measurement of a change in time would be written as what DT DT this is not a derivative I mean okay yes it is a derivative but it's not like all derivatives are what ratios Rao okay that's what they are there's no magic I mean I know I know you've been in class and then take a der x 2 that's that's monkey work okay well from alpha can do that right the power behind this concept of derivative is that we're changing things we're changing something compared to something else in the case of a velocity it's a change in position of a change in time what my acceleration be change in velocity over change in time now can I take the derivative of a velocity function with respect to T and get its acceler function yes but that doesn't change the fact that it's it's change it's a ratio we often use a bar well sometimes we don't do anything uh and you can see here that I made the mistake I I did it over the a just by reflex okay that bar is used to indicate that I we're talking about an average we're using a Delta sometimes it's dropped sometimes it's implied where you'll see in the calculation that a Delta is involved and if you see the Delta then you know you're dealing with averages you're dealing with a over a period of time but when we we reserve the Little D's and we reserve the symbol V and a with no bar over the top to say no this is the acceleration right now what would change in acceleration meas it's called a jerk and it's in units of jerks it's yeah it's kind of a measure of how fast the acceleration is changing so can be used like in vibration sometimes and stuff yeah but it's called a jerk change in acceleration we don't do that in here okay um I ran out of time for that quiz in the last when did we get out of here 9:15 right 920 I don't know what it is okay you're stuck for the rest of the day no let me plant an idea in your brain that we are going to use on Monday I I spent a lot of time talking today because I I just assumed you had read the book or something right so on Monday what we're going to do is we're going to get into the nitty-gritties of working with acceleration velocity and time we're going to we're going to pull some equations out we're going to start problem solving okay th this method that I'm going to teach you right now and continue on Monday is the key thing that you are supposed to be learning in physics for it okay I know that there's kinematics and energy and forces and gravity and all these Concepts but really what we need you to learn is problem solving a systematic approach to figuring out anything and by anything I mean anything I use this problem solving method when I do my taxes okay that this problem solving method I personally have boiled down to four steps these steps mostly go in order but there's quite a bit of Wiggle in terms of going back and forth and around again it's supposed to be a circle supposed to be like an iterative thing that you do okay but what I want you to take home right now is is the idea of well this analogy let's say that you um you're told that you need to build a house okay what are the things that you need in order to build a house correctly what like gear tools that kind of stuff materials okay okay so knowing how to do it all right so we got materials we got knowledge you have all the nails and wood and Concrete in the world and knowing how to do it but you're not going to be able to do anything with it if you don't have a plan because it's going to look insurance it's going to look really wonky without that plan right but there's another key thing that's missing what are the things you use to make the measurement what's a screwdriver what's a hammer it's a duel you need materials you need a plan you need tools right in order to build a house okay problem solving what we are trying to get you to do the problem solving method is often where you're going to formulate the plans the materials in this class you're are going to be given to you in the form of word problems yes word problems this is your worst nightmare come true okay the tools will be the equations the physics the stuff that comes do you approach a hammer and ask it how to build a house Hammer doesn't know in the same way the equations don't know never start with equations if you can help it sometimes sometimes it's your only starting point but most of the time you are going to want to go straight Mr I always tell Mr B just tell me which equation to use you're saying don't make me do physics right just let me do Algebra okay the whole point of this class is to know how to use the tools so when you're going through in reading so you're going to do chapter one you got to do your chapter one homework right okay it's do the Saturday so Friday's a great day to come in and get help on that um and then chapter two reading you need to start over the weekend because on Monday we're going to really dig into chapter two right okay so as you're going through you're not going to understand understand everything but you're going to see equations and you bre there's going to be like little yellow ones or outlined ones this is the key equation you know I'm going to write that one down I do it those are just tools they're hammers they're screwdrivers they're socket wrenches they are not the house they are not the plan they are not the materials right keep that in mind right because so many students make the mistake of thinking it's just the equations that I need they're a piece of the puzzle I we'll see you tomorrow in whatever lab you are in or trying to get into please make sure not to miss tomorrow if you can't if you can't if there's something going on email me