Lecture 8 Sec 0002, Sept. 17, 2015

ok okay my wonderful students sorry I was a little bit late coming through the rain as all of you were so a couple things I want to make note of with you yesterday I revised and updated the clicking data for lectures five six and seven this is lecture eight the end of our fourth week of classes and some of you may have noticed that you’re clicking answers and clicking correct numbers may have changed and that is because there was a problem with one of the formulas that in the spreadsheet i was using that has now all straightened out everybody should be correct and up-to-date this is what the participation rate looks like for both sections more this section in the morning section we have a total enrollment of 582 right now out of the six questions that I have asked for the last 3 or the previous three lectures 343 out of 582 have answered all six and that is good now a hundred out of the 582 have answered five out of six and then there’s dribs and drabs and there’s 34 students that are not on the scoreboard at all they have zero answers and that is not so good I know some of you are still you know fighting your financial aid stuff so you it’s getting late and so if you if you can’t get it done for next week it’s going to start really hurting your your grade but these guys up here they are looking good for 25 out of 25 if I were to do semester grades today but we still got another you know three months to run so you know we’re not going to be getting close to the time until the end of november though thanksgiving but if i were to do grades today these guys would get 25 of 25 then five out of six that’s 83.3 three percent so that’s below 85% these guys down here a hundred people I would have to calculate based on the eighty-five percent factor so if you’re above eighty five percent of just 25 points you get them all below that you have to calculate but it’s I want to go another week or two before I give you an example of how the grades calculate for these guys down here because right now it’s kind of boring but in a few weeks we’ll have students will have about 20 questions on the books and we’ll have students that are scattered a little bit more indicative Lee but most of you are here in six out of six territory and that is where you want to remain in the hundred percent participation category and most of you will and so a few of you will maybe be a little bit below hundred percent but almost everybody is going to be above eighty five percent so don’t worry about that it’s still early days and like this guy here four out of six that’s sixty-six percent there’s not going to be many of you with sixty-six percent participation at the end of the semester everybody’s going to be way out there so it doesn’t look that interesting right now but I will do it an example of this with you in class directly sometime after exam one and then we’ll have plenty of questions on the books now we’re going to have some clicker questions today so you may as well get them out I want to recap some of the conversation we had concerning Aristotle and Galileo and that mythical frictionless plain the horizontal plane and the Ferrari that we drove off the cliff at a constant speed of 20 meters per second now mr. Aristotle from Greece would have said hey man if that thing is moving

even if it’s a constant velocity there’s got to be some push acting on it that was his approach and it it’s not you know it’s not he was wrong about that but it’s definitely understandable that he would make that point about motion Galileo was able to say no man if it’s at constant velocity there’s no there’s no you don’t need a push force to keep it a constant velocity it’ll do that on its own and Galileo was able to prove it geometrically now I want to go over that geometric proof again with you a little bit slower let’s see if we can put it back together similar to what’s in the textbook so this will reinforce your reading in Chapter two so let’s simplify the argument we’ll talk about a one-kilogram object so that’s like a litre bottle of water give or take a gram or two and we’re going to say it’s going at a good nice even one meter per second 1.00 meters per second and let’s say that this object has some generic unit of force now we’re not saying metric units a force just yet but some generic unit will say it has 1 1 unit of downward weight force and in the diagrams yesterday and in the textbook I use the symbol w capital W for that weight force okay downward capital W for weight and so let’s say that this object if it has a 1.00 generic units a force downward from the weight pull from the gravitational pull of earth then what that also means is that you have to push it upwards by the same amount of force so if you exert 1.00 a new generic units of force upward you’ll balance it out you’ll support it it’ll be stable okay and that was the upward vector in lecture and in the textbook labeled Capital y right so this is our simplification now let’s get back to this dialogue between Aristotle and his student Galileo the student has become the master Galileo is now the master of Aristotle and I’m sure Aristotle if he were still alive he would say you get it you go Galileo so here’s Aristotle again making his claim now this one’s in terms of the simplification that we just looked at and so here’s what Aristotle would have said that leader of water needs a small push and and gala and Aristotle says it needs 0.100 generic units of push even on the mythical frictionless plane all right that’s what he was saying he you know it’s it he had this idea that if it was moving something had to be moving it actively it wouldn’t just move and stay in motion on its own all right so if it’s moving at one point 0 meters per second he said there’s going to be some little unit of force and we use the label p lowercase p for that force and Galileo said no way Jose because point 100 generic units of force hey I got a ramp that that’s the that’s the downward excel the downward force on the ramp you know so if you if you tell me you need one point excuse me if you tell me that you need 0.100 units of force on a horizontal galilea said no that’s not right that’s what’s way too much because that’s what you need on a ramp and he said I can even build the ramp for you and show you and I hate back to be backed up his claim with action with something that he could construct geometrically so here it is this a little version of it and we’re going to blow this up in just a second but first we got a question here capital d is the force going down the ramp remember how last time we said you know of if you’re going if your if your ramp is vertical you don’t really have a ramp

all of your weight force accelerates you along that ramp but if you tilt the ramp so it’s slanted you get a little bit of force down the ramp but most of its being absorbed by the ramp now so you have some along the ramp and some perpendicular to the ramp okay depending on the tilt of the ramp and Galileo was saying I know how to get that down that down ramp fraction it’s just you know proportional triangles which we did last time and here it is I mean you know he said look if if this thing is a way for us of one and you’re saying that on the horizontal it needs point one units of force then I say let me build a ramp of this proportion where the hypotenuse is one unit of distance and the the height the altitude is point one unit of distance ok so the forces that Aristotle claims tell Galileo how to lay out his ramp and he said if you do that for this one kilogram object that has a one generic unit of force wait then the down ramp fraction of the force you know because on this ramp it’s not going to it’s going to be like this you know you’re going to accelerate but it’s not going to be 9.8 so that the fraction of that that acceleration that you get the fraction of the full weight force down the ramp is is basically computed this way all right and so Galileo says this ramp gets point 100 generic units of force to propel the other so you don’t need that that’s way too much for horizontal horizontal with whatever you find for a ramp the horizontal is going to be less than that all right so if you tell me that point 100 is what you need on horizontal I can I can make this rampant say no to wait a minute point 100 is what you need for this ramp it’s not what you need for the horizontal now whatever you do point 100 that’s that’s way too much for horizontal and no matter what number Aristotle said all right Galileo so point 100 won’t cut it let’s cut it down to zero point zero 10 units of four and Galileo would have been insane I got a rant for that you know and so Aristotle’s are right all right ok I get the ramps let’s just go down to a thousandth of a generic unit 0.001 and galilea would be able to say I got a rant for that you know air style airy baby whatever you give me I could build a ramp and and basically you’re out of here Aristotle I’m the I’m the master now and Galileo was able to prove basically that there is no minimum value for pushing any object hold on this on this horizontal my it’ll just keep going it doesn’t need any Newton’s of force all right any positive numbers too much and therefore on the ramp to keep going it needs exactly zero on the horizontal plane and that my wonderful students is actually Sir Isaac Newton’s first law of motion which we will tackle in just a few minutes but before we do that I want to look at a few more ideas related to the reading and to the homework so take your clicker out and we’re going to click through some questions starting with some multiple choice and then we’re going to do some numeric and some alphanumeric questions so hold on to your hats because here we go question number one and by the way this is frequency BB if you just get your calculator and it’s not you’re not you’re getting the no base it’s not working right hold the power button down until the square flashes and then type in BB bravo Bravo and you’ll be on the system alright so go ahead and vote for this this question you’re riding on the ucf shuttle bus but if it’s crowded you have to stand in the

aisle etc etc so what direction do you choose 30 seconds 10 9 8 7 6 5 4 3 2 1 0 okay we got 176 students Wow we should have about 50 more students clicking here I guess a few of the students floated away or something in the rain last time okay you guys did good ninety percent of you got this one correct so if the bus accelerates forward you’re going to attend it or if you’re if you’ve got fuzzy dice hanging from your rear-view mirror you know and you goose the the accelerator forward and the fuzzy dice are going to kind of swing backwards so this is good now that’s a pretty basic concept let’s take a look at this one all right you’re moving at constant velocity does that guarantee that no forces are acting on you read very carefully as I say to one I say to all read carefully 20 seconds 10 9 8 7 6 5 4 3 2 1 0 all right and see what you I see there’s a lot of geniuses in here all right you know what it’s interesting the first hour class they were all over the place you know this one you’ve got sixty-eight percent correct they didn’t even have fifty percent correct they had forty two percent correct so you guys you guys are genius this is the genius section I guess either that or you talk to your your classmates from the first hour but the answer to this is is d and that is a case or that is a concept for which this skydiver is an example terminal velocity raise your hand if you’ve ever done skydiving anybody ok that’s a pretty good number now raise your hand if you’ve ever skydive without a static line in other words you jump out and they fall for a while and you get to pull the ripcord yourself raise your hand if you’ve done that nobody so nope just you yeah so you like so in other words the first time you jump you got to jump with your instructor and you’re wired up to your instructor I guess or they they pull it for you as you jump but eventually you get to jump and then decide when to pull the ripcord right yeah so when your skydiving what happens is you if if you really are up there when you jump out of the airplane and you just fall and it must it must feel great it must be really fun no it’s not you totally have a heart attack well I mean I have a heart attack getting out of the plane but once you’re out you know why not enjoy it at least until you reach the ground anyways I don’t know if

I could do it but if I did do it I’d enjoy it but if you do jump out of the plane and you get to pull your own ripcord after a second or two you’re going to reach terminal velocity now terminal velocity is a situation in which the downward pull of gravity is completely balanced by the upward push of air resistance you know if you put you if you’re driving down to Miami on the Turnpike and you roll the window down and put your hand out you’re going 65 you put you you’ll feel a little bit push from the from the air going by the car now if you’re going you know like a hundred miles an hour or faster like a skydiver you feel a lot of force and eventually you’re going so fast downward that the upward air resistance exactly balances the downward wait for us now the downward wait for some re is the same all the way down but as you accelerate you get more and more upward eras istence until they exactly balanced up and down and then when they balance up and down you stop accelerating that’s the terminal speed or terminal velocity Colin yeah Colin saying if you change the shape of your body the shape presented to the wind basically and the answer to that is yes just think of a sailboat you know sailboat trims sales or puts up a jib or spinnaker depending on you know how they want how fast they want you know how the wind is going and stuff like that and similarly for a skydiver if you know they this guy is doing a belly flop right pretty much okay but if he were to tuck into a ball you know bring his knees up and hug his knees he’d he’d start accelerating again okay but he’d eventually get to terminal voss a different and higher terminal velocity if he jumped feet first from the beginning instead of you know jumping like this like whoa excuse me my microphone just did a belly flop if he pulled on a second if he went to the the edge of the plane and just kind of stepped off and went straight down and kept his feet down and then you know he did assume a terminal velocity but then as soon as he did a belly flop I’ve turned himself you know horizontal and took the belly-flop position he slowed down and because he’s presenting so much area sail area to the wind that it’s it’s giving him a lot it’ll slow him down and then he’ll it soon a slower terminal speed in that case and that’s what a parachute does a parachute present it effectively gives you more sail area that you present to the wind it’s above you and so it’s so basically you’re the area that you present to the win is no longer as significant as the area that the that the parachute does and so you you know you you pull the ripcord your parachute comes out and anybody that is with you and they don’t pull the parachute they just keep on going so you pull the ripcord and your buddy you know weights another second he’s looking at you up here like this you know your way up there because you seem to have slowed you have slowed down as soon as your your parachute grips the win okay so so yeah it’s it’s the the amount of area that you present to the downward or to the upward flow of the wind of the air it it determines your terminals velocity and so that so what do you pop your parachute your terminal velocity is now you know five miles an hour or whatever happens to be you know so you don’t totally kill yourself when you hit the ground I mean if you still break your ankle if you do it wrong but but you know I’ve seen what was that show that movie san andreas with the rock and he parachuted into the state well some guy so the stuntman parachuted into Candlestick Park in San Francisco anybody see that movie Paul you guys man I should make that a homework assignment that that was a cool movie but anyways say parachutes in and he just came in easy as a you know light as a kitten you

know so depending on your parachute you know you have different terminal speeds but now this is a kind of a nasty question because if you look at this you know it’s and i can give you questions like this on a on a midterm or final little problem there’s two yeses there’s two knows and there’s one yes and all so somebody you know tells you the answer is yes yes yes well which one do you choose and see this is the kind of thing that you have to be able to handle you know it’s not enough just to say true or false but you want to be able to be in the position where you can say why it is true why it is false why the answer is yes why the answer is no now this one the sir is no the second no but the first snow is horrible and that is because forces are related to acceleration make a note of that option C is no good ski no good skeeza is kind of a Polish term n 0 g 00 d sk i know good ski after a some polish guy that was no good anyways so this is no good it’s the worst they definitely are related all right now I got another question for you it’s going to be about this parabola for which the launch velocity V subscript I better make a note of this 10 meters per second comma 19.8 meters per second so it’s horizontal component of the initial velocity is 10 meters per second 10.0 meters per second and then the vertical component it’s going up it’s a positive 19.8 all right that looks nice okay so i got 19 point eight meters per second going up at the start now that gives me a velocity vector initially that looks like this all right and that arrow the tail of it is right at the it’s right here at the launch point so this is where the base ball leaves the bat if this were a home run heading for the outfield all right and it goes up now eventually the direction changes and the speeds changing everything but initially that’s its velocity now what I want you to do so here it is just kind of this vector here all right so there’s your initial velocity now what I want you to focus on is the landing point ok so the landing points over here and what I want you to answer to the best of your knowledge is and I’ll give you a chance to do this in just a second nope what is the vertical component over here when it lands just before impact all right so go ahead and sketch your parabola sketch in your initial velocity vector here just try to do a good you know job you know if you’re if you’re not another Leonardo da Vinci that’s all rights to your best all right and with your iclicker I want you to hit the refresh key because you’re going to put a numeric answer in there all right and I’m going to give you the diagram back in just a second so hit refresh and when you hit refresh you will get the number one and so what I want you to type in is the vertical component of velocity V subscript F just before impact in other words what’s this what’s this number right here okay now if you have to type in a negative number you know go ahead negative two point three year and give me your answer to the nearest tenth of a meter per second alright so go ahead and stuff and as always definitely talk it over with your neighbor if you feel like it because talking with a neighbor really helps sometimes question what’s that what did I say the what that’s 19.8

right here yeah that 19.8 is the vertical component of the initial velocity that’s VI y and this is the horizontal component VIX right you okay 30 seconds you are you supposed to what there’s no formula you gotta think your steer thinking like an engineer what’s the formula that’s what they do they go looking up in the book where’s the what’s the formula i use for this but what you really want to do is be able to think because it’s actually a simple answer if you think carefully 15 seconds ten nine eight seven six five four three two one zero get your answer in camp closing it this time this time frame it where’s my all right Club really closing it i really mean business this time but let me see what you guys k hundred sixty nine students well it looks like we got a bunch of geniuses here because the answer is negative 19.8 now Silencio that’s what my mom used to say when I was a little kid if we were making too much noise she would say Silencio and we should we know she was very big trouble now look at this look at these answers now sixty-two percent of you got it correct good another six percent got 19.8 no that is not wrong not that it’s not right it is wrong 19.8 is is this that’s the initial velocity the horizontal motion doesn’t change its tannin 10 both times because there’s you know there’s no such thing saw rosano gravity right but what changes is the vertical component because of gravity it loses 9.8 meters per second of upward speed or gains 9.8 meters per second of downward speed for every second on the trajectory now let me get my cursor back here for a second all right so this is your initial excuse me this is the final velocity vector V subscript F go ahead and jot that in kind of draw that into your diagram right down here right here all right now it is comparable to V

subscript I the initial velocity now I’m going to copy I’m going to move VI over such tail to tail with VF all right now watch here it goes all right so there’s VI tail to tail now it belongs back over here on the left so let me bring it back over there but you can see that they are mirror images you know one’s up one’s down and that is the effect of gravity right now final note side note for any path no matter what the path if it’s straight or if it’s curved the velocity vector that arrow is always tangent to the path so my arrows here just gracefully touch at one point only that’s what it means to be tangent okay and just make it over that no matter what curve we have for trajectory the velocity vector if you do want to try to draw it in it has to be tangent so you could draw a little tangent line and then the velocity vector based on that tangent line now here’s a picture from the internets of a home run trajectory now this is a guy named Hunter Pence he hit this home run out in denver back into 2013 and 476 feet apparently this is like the ginormous home run it went all the way past the bleachers apparently out here it hit this brick wall behind the concession stand that’s the concession stand all these people are out here buying hamburgers and hotdogs and stuff and whatnot and so they’re out there by hot dogs and hamburgers and meanwhile Hunter Pence ear ox woman gotta dodge God’s baseball is flying in from outer space that is a monster home run and on this trajectory the vertical component of the motion is changing but not the horizontal okay so if you if you neglect air resistance it’s a perfect parabola alright in reality it’s a little bit less than a parabola but it’s pretty close and so the question is why is that why is Hunter Pence home run is monster home run of 2013 at it I guess that Safeco Field out of Denver or whatever the name of that baseball field is uh it’s a mile up in the atmosphere my life City Denver and so the question is you know why you know why don’t the horizontal components of the motion change you know velocity that arrow is changing right there’s the there’s the launch velocity V subscript I but the horizontal component of the velocity doesn’t change its always 10 10 10 m/s all the way through or whatever it is you know for him it might have been 30 30 30 meters per second all the way through I mean that thing was a rocket so what I’m going to ask you now is an alphanumeric question I want you to hit the Refresh key again and I want you to build and answer build an explanation for that question using this code table let me start the question for you you should start what do you have a the letter A if you get to refresh key you should have the letter A and here’s your code table over here now there’s no french fries there’s no sharks there’s no leave Britney Alone this is a regular physics question and I could ask you a question like this on the midterm or the final and I have done that on midterms and finals so put together an answer why do the horizontal velocity components why don’t they change now vertical we know why that’s changing but why don’t the horizontal how would you write it now think of an answer and you might not have anybody else answering the exact same way that you do and it might be perfectly correct there

might be 75 different correct answers in this class just depends on how you word it so put together and put it in your notes as well the question as well as your answer okay now if you spell your name I’m going to know it so so don’t write Jonathan or whatever your first name is but do try to put together a good explanation you I hear those clickers clicking and definitely talk with your neighbor talk it over see what they think if you have somebody that you’re sitting with and if you sit next to darienne you could talk it over with darienne yo front row young lady with the white shirt the white top you’re sitting next to darienne so she knows all the way through all this stuff so don’t be shy about talking to her or to anybody it’s really good I see you guys trying to point to different things and it’s good yeah you might have a question like this on midterm 1 a week from today I can’t tell you what’s going to be on the test but if you think about this one you might be happy next thursday afternoon one minute don’t forget to hit the send key 10 9 8 7 6 4 wait a minute I was looking at the numbers here okay 10 9 8 7 6 5 4 3 2 1 0 okay slackers get that thing clicked it come on one more we’re at 175 you know we all right there you go all right now let’s see what you guys have got whoa ah you know this is kind of interesting s zq look at that only seven people typed in that answer now I’m not saying it’s correct but it’s the most popular answer let’s see if it’s correct szq force never change force never changes that is partially correct the gravitational force is always down but that one would only be partial credit because you would want to mention that the force is downward the gravitational

force is downward and never changes so that was partially ok CZ q let’s look at this one CZ q directions never change incorrect CZ q Charlie Zulu Quebec is incorrect the change the direction of the baseball definitely changes you know what’s going this way on the way up is going this way on the way down that’s a change let’s look at a couple more here n VZ 0 g November Victor Zulu Oscar golf let’s see that’s that’s this one envies EOG ok envy horizontal position the horizontal velocity n VZ never has g ah no n VZ 0 g is incorrect that’s mixing apples and oranges I can see what if you now i’m not you know don’t i don’t make a mistake if you voted for that or if that was your answer I’m not making fun of you I’m trying to talk about the things that I see I don’t know who it is I won’t know till later when I analyzed the spreadsheets but let’s look at one more let’s go way down here whoa here’s a long one ah envie el que veo PQ whoa let’s see what that one is okay NV horizontal velocity and BLK a horizontal velocity from up well that’s no good beo PQ and has no veo PQ and down up and down has PQ not changed that’s kind of a mix I I’d have to look at that look carefully let’s look at one more here all right let’s look at this one one student voted for n VZ 0 a a horizontal velocity never has acceleration whoa whoever did that you are right on the money I’m not going to look for a show of hands but oh and I know it don’t everybody put up their hand cuz i know it’s only one person this tells me this hold on a second this tells me only one person voted for n VZ OA but that is a crackerjack answer so whoever answered that you can tell me on email tonight in webcourses that is well I’ll know anyway as soon as I grade this that’s a lovely answer so I’ll probably give you some more I’ll analyze all of them tonight and grade them and it’s just one point or zero and then um over the weekend i’ll post those and then tuesday we’ll go over some more of the nice answers and just to reinforce do expect to see a question at least one question like this on the midterm next week all right let’s talk about the three laws of motions we’re going to take some notes and we got one more clicker question coming so don’t put your clicker away now Galileo’s whole thing about defeating Aristotle using ramps that there’s no minimum force the minimum is zero that’s all you need on a frictionless horizontal plane to keep in motion because the object in motion is indifferent to rest or servile ossett e being in motion or being at rest at Sir Isaac Newton wrote it down approximately

this way every object retains its state of rest or at state of uniform straight-line motion in other words constant velocity unless acted upon by an unbalanced force and that is basically his first law and it is the but it was developed by Galileo and Sir Isaac Newton was famous for saying if I have seen far it is because I stood on the shoulders of giants he stood on the shoulders of Galileo and Kepler now here’s an example of the first law in the manner that Sir Isaac Newton intended applet an apple tree balanced forces all right if you think about an apple in an apple tree it’s attached to the stem you know the stem of the apples attached to the branch and it’s got some tensile strength and so that stem produces some upward tensile force on the Apple and it balances completely with the downward weight force the gravitational weight force which is down and if it does balance the Apple stays at rest it stays on the branch but you know if if you have a fruit tree in your backyard or your parents’s backyard or anywhere you may go around here Florida their storage trees all over the place grape fruit trees tangerine trees you know that the fruit eventually falls to the ground well when that happens the stem weakens you know it dries out eventually and it loses a little bit of its tensile strength the balance will fail and down it goes okay and if you’re Sir Isaac Newton taking a snooze under the apple tree it’ll you know fall on your coconut and that’s how they say that he started thinking about gravity and universal gravitation it’s one of those legends that he never really somebody he must have told somebody but nobody’s been able to a hundred percent verify that that actually happened just like with Professor Galileo in the Leaning Tower of Pisa everybody thinks it happened but he never really said yep definitely i did it on such-and-such a date you know so it’s it’s a legend that everybody believes in kind of like Tom Brady is a good guy that’s a legend that everybody believes in don’t get me started on that okay anyways here’s another example Newton’s first law and let’s think in terms of a bus UCF shuttle bus everybody in here is probably taking the shuttle bus or most of you anyways from time to time okay if the bus moves forward you’re going to lurch backward we talked about that in one of the clicker questions okay and that’s because you ten if if you’re not bolted down to the bus you’re going to want to stay in your original state of motion so if it speeds up it’s like speeding up below you and if it speeds up forward you know your feet are going to go for your feet are kind of attached to the bus but the rest of you is going to you know tilt backwards so you get a whoa you get a steady yourself right similarly if the bus turns to the right you’re going to want to keep going straight and and that feels like you’re going to bump your left side into one of the seats are into your neighbor on your left alright so left and right forward and aft those are separate motions and that’s why they have all those bars and braces and stuff on the shuttle bus you know even the seats have little handles that you grab ahold of for safety all right and you usually use that unless your bus never changes its state of motion but here at UCF I don’t know those guys seem to drive like maniacs anybody ever notice that they just drive like really they go really fast and they slow down and they go really fast again I don’t get carsick with those guys alright so those are separate interactions same thing with this baseball if you think about it here’s here’s the picture of this home run out

in Denver and it’s got separable motions the vertical component and the horizontal component the horizontal component is unchanging but the vertical component is definitely changing all at every instant so so on the bus forward and aft starboard and port up and down you know if you hit a pothole you’re going down you’re going up on the way out of the bottle yeah those are separable motions so we have to keep those keep track of those stuff and so if you if you the bottom line is you’re going to whatever state of motion you’re in you’re going to tend to stay in that state of motion you know and if you get jostled left to right or if you get Joshua forward or back or up and down you know you’re gonna thought you’re going to feel it okay now if you’re not in a constant state of motion that’s because of an unbalanced force and so just like you know this transformer here this is one of my favorite transformers Jetfire his father was a wheel the first wheel and you know jet jet fire was you know got these guys over to Egypt and everything all their adventures and he really got him in a state of motion so let’s talk about states of motion for unbalanced forces this is where Newton’s second law comes in this is the heart of his whole system of analyzing motion because this is the one that allows you to generate an equation of motion or a time evolution equation as we say and predict future states of motion if you have enough in the chill information okay so here’s the first thing he did he said all right add up all your forces and if anything doesn’t balance then that’s the net force okay so as an example let’s think about Dwight Howard and LeBron James okay if LeBron James let me get my cursor over here if LeBron James is pulling to the left and Dwight Howard is pulling to the right you know one of them is going to be stronger so in this example let’s say that Dwight Howard is pulling to the right with 100 generic units of force and that LeBron James is pulling to the left with 80 generic units of force all right so he’s pulling leftward so we give him the number negative 80 right now Dwight Howard is 20 units stronger and that means that the net force is 20 units of force positive or right word and so that’s this arrow right down here okay so between those two guys they don’t perfectly balanced and so ever who has so whoever has more pull that’s where the net force is going to point towards that guy in this case Dwight Howard now another concept that Sir Isaac Newton said was figure out how much push force you’ve got figure out your your net and then if you have more net force you’re going to get more acceleration all right now here’s the colloquial example for that think of Arnold Schwarzenegger are pushing the grocery cart a loaded grocery cart at publix versus a little kindergartner pushing the same card little kindergartner is going to accelerate it but it’s going to be kind of pokey but Arnold’s going to really jam it he’s going to really give it some good acceleration all right because he has more push force third thing if the shopping cart has more kilograms if you load the shopping cart like if you load it with water water is pretty heavy versus loading it with cheering the same volume of cheerios boxes of Cheerios or ramen noodles that’s really light okay raise your hand if you’ve had ramen noodles for dinner last night I know man is pathetic Rock I know I like them too you know sometimes it’s the only thing you have any way so if you load up your cart with ramen noodles no matter who

you are you’re going to accelerate it at a higher acceleration than if you load it with the same volume of water because water is more dense you know water is one killer one kilogram for every leader ramen noodle is like about one gram for every cubic leader so now he put it together into this mathematical formula and hopefully this makes sense to you the acceleration is the quotient of the net force divided by the mass all right the net forces of the numerator okay more net force more acceleration the mass is in the key is in the denominator so if you have more kilograms of mass that’s in the denominator now you have a smaller quotient so not as much acceleration and it worked this is his simple law F net over m equals acceleration ay here’s another way that it is written in a little more compact way we’re in the engineering building Harris engineering if you go out there in the hallway and interview 10 engineering students in asking about what’s Newton’s second law this is the one that they’ll say F equals ma okay its equivalent it’s just a different way of writing a little more compact okay so f equals ma equals F net over m those are Newton’s second law now a couple things about it I want to go a little bit deeper into it and we have one more clicker question coming up so and actually you know what let’s let’s skip ahead let’s see if I can