hi, i'm paul hewitt, the author of conceptual physics. you know, physics is a study of nature. the way things connect to one another. and these connections are underlined by the concepts, concepts which are beautifully expressed mathematically. but the focus of conceptual physics will be the beauty of these concepts in english. the equations of physics will be seen as guides to thinking, much more than recipes for numerical problem solving. so the idea is the comprehension of concepts first and then computations later. ideally, in the laboratory where they're really meaningful. this tape you're looking at right now is the first. it's the intro of a series of more than 30 tapes. and this is a long step from where i started: video one of one my classes. that's like back in 1974. let's take a look at my class as it looked like in 1974.

enjoy. matt, you wanna come here and try this? could i have one other volunteer, please, to pick up the anvil and put it on my head--chest? [laughter] right here. no, no, no, yeah-- right over here. [laughter] yeah. around--yeah. okay. yeah. that's good. it's for science. [laughter] do it again. [makes sounds] [laughter]

black and white. then 10 years later, in 1984, my good friends dave vasquez and craig dawson came into my classroom and videotaped the course again. and 12 of those ended up as the tapes distributed by addison-wesley. one of those, i would like to show you now, features my good friend paul robinson, who turns out to be the author of the laboratory manual to the conceptual physics program. let's drop in in that class. don't touch it now. don't touch it now. okay. you'll be harmed less if you touch it now. you can trust me. okay. here? okay, right there. that's right on. yeah. [laughter] oh, that's beautiful. stay holding it. okay. look this way. yeah, that's nice. oh, that is nice. that's fantastic. look, look, look, look. oh, that's nice. that's nice, very nice.

okay. now, i tell you what? could we all hold hands today? yeah, okay, yes, yes. let's all hold hands. back here, john. right--that's it, right, just come here. let's--here we go, go on. okay. dave, get that. okay, okay. okay, don't break the chain now. anyone wearing pacemakers here? [laughter] okay. i hope not. if you're wearing a pacemaker, don't participate. okay? come on, here we go. it's okay. you back row types. those are your neighbors you're sitting next to. hold hands, it's all right. okay? [screaming] [laughter] okay, watch this, gang. inertia, huh? card, coin, huh?

[applause] yeah. a body at rest tends to stay at rest. i'll show you a nice one. this one was shown to me by my friend marshall ellenstein. okay. get a little hoop like this, balance up--on top like this. [laughter] try again. marshall ellenstein. [laughter] [applause] let's take this and-- let's show, by the way, this apple. and this as well.

these are sharp nails, gang, okay? i don't like this-- about an inch apart. if you don't know what an inch is, think about 2.54 centimeters, about 2.54 centimeters apart, all right? and paul is gonna... are you sure these are teflon coated? no, these are the real thing, honey. --about to go. and you know why we don't do it the other way around? that's a good question. [laughter] this really is dangerous, and paul is a little more foolish than i am. [laughter] no, no, no, no. paul-- thank you, norm. okay. [laughter] on your back, robinson. all a day's work. yeah. it's for science. have to have red socks.

[laughter] okay, you guys protect yourself, protect yourself. okay, yeah. okay. okay. here we go, gang, here we go. all right, one, two-- wait, i should tell you. [laughter] i should tell you. this is not mind over matter. it's not what kind of granola or bean sprouts or meditation that paul does. you know what this is all about, gang? physics. physics. yay. okay, let's see it. here we go. 1, 2, 3... [applause] in 1989 and 1990, i took a leave from san francisco and taught conceptual physics in honolulu, at the university of hawaii. there, a small part of my class met in a tv studio classroom

and the whole course was videotaped, and that makes up the present series, which has been edited by my good friend marshall ellenstein. you'll notice in the series that the students are mainly first year university students. but they could as well be first year high school students, and you know why? because the physics is the same. let's drop in on opening lecture. enjoy. okay, gang, welcome to conceptual physics. i'm gonna give you a lot of lectures this semester. and the lectures i'm giving are only the highlights of the course. guess where the learning takes place? reading the material and getting together with friends and talking about the ideas. so what i'm gonna do is highlight some of the ideas and talk about physics. but the physics you will learn, you will learn from your textbook and working in groups in your laboratory. hmm? now, first of all, what is physics? today is the day not to take any notes, okay? sometimes, if something's important, i'll say, "hey, gang, put that in your notes

'cause you might need to need that later on." yeah? but for now, hang loose. what's physics? let me ask you a question. did you ever take a friend to a game--basketball game, sports game, any kind of game-- and that friend doesn't know the rules of the game? and you're digging on the game. you're really, really enjoying it. you find out your friend is kinda just sitting there, looking, right? can that friend appreciate the game if the friend doesn't know the rules? no. you gotta know the rules of the game before you can appreciate it. and guess what physics is, gang? it's the rules of the game of nature, the physical world. we're all in a physical world which has surprisingly only a few rules, and those rules are what physics is about. and when we learn those rules and we see how those rules apply to what's around us, then the physical world means more to us,

and our position as a living being is elevated, and we can interact better with the physical world. it's like a couple of people walking through a park. one is a botanist and the other is an everyday person like you and me. that botanist takes a 10-minute stroll through and that botanist sees all this stuff. you and i walk through, like that. i say to you, the botanist lives for a longer time than we do because the botanist is alive to what's going on, and we don't notice it. now, see, you're gonna find this course isn't something just to read in your book. this course is gonna apply to you at home, not at home, everywhere you are. and you guys right now see physics as something that's between the pages of this book. i guarantee you, you're gonna to start to see it all around you. and that's why you'll like the course, i think. now, once you learn the rules of the game, then it's nice to know how to keep score. and you can do that in the laboratory. so laboratory is keeping score and the lecture is what the rules are all about.

now, i'm not gonna define physics more. all i'm gonna do today is ask a bunch of questions and these questions i want you to think about i'll tell you this. you might think you know the answers and as it turn out later on, that maybe the answer you had was wrong. but i'll bet you this, by the end of the semester, you guys will be able to answer all these questions comfortably. okay? here's an example. i got a piece of clay and the keys. clay is significantly heavier than the keys. when i drop them, they both fall together. why didn't the clay fall faster? hc? how come? [laughter] we gonna find out there's a reason for that. and we gonna find out that the fellow by the name of galileo, who first did that, the leaning tower of pisa. he was reported to have dropped a heavy, heavy ball and a light one, and foom, they both fell about together. and at that time, people thought that heavy things fell faster than light things.

and galileo demolished all the physics at that point by showing that, wow, it was wrong that heavy things fall faster than light things. that's only in the presence of air resistance. but without the air drag, both fall together. and galileo couldn't answer the question "why?" and guess who's gonna be able to answer that question "why"? look at the person to the left of you. look at the person to the right of you. now, look at yourself, gang, okay, 'cause we all gonna be knowing such a thing, huh? why that's true. why is it that a heavy rock will fall just as fast as a little pebble when air resistance is not so big to make a difference? why? hey, how does a rocket move, a rocket propel from the sky? is that physics? rocket--suppose rockets-- what makes a rocket keep going? is it something like this? you guys ever been in a swimming pool? you're in the pool and you get in the edge like this, and you kinda put your feet up and you--you push out like that. you kinda rocket across the pool. does a rocket work a little bit like that? check your neighbor. the answer begin with an n.

[laughter] it turns out no. a rocket doesn't work like that. you know, when you push against the pool, you push up. what's a rocket pushing it against? air. especially when it's above the air. what's it pushing against? what keeps it going? how does it work? air interaction. we're gonna be learning these things. chapter four. we say, now, what goes up, comes down. we don't really say that anymore. we used to say that before in the fifties. what goes up, come down. now, what goes up sometimes doesn't come down. and when it doesn't come down, and we call it-- it begins with an "s," ends with atellite. try it. satellite. go ahead. try it. satellite. yay. okay? that's what a satellite is. sometimes, things don't come back down. how come? how many say, well, there's probably no reason for that, that's just a characteristic of satellites? come on, gang. there's a reason for such a thing. we're gonna-- some people will say, "oh, it's beyond gravity." guess what, tilt, uh-uh. that's not beyond gravity.

if the object were beyond gravity, you know what kind of path that we take? anyone know that already? let's suppose a satellite going around and round and round, all of a sudden, gravity cut off. boom. what's the direction of the satellite gonna be? straight line. straight line. straight line. just keep going, going, going, going, going. but gravity pulls it into-- why doesn't gravity crash it to the ground? hc. we're gonna be learning that. that's chapter four too. you guys, when you're walking out a fence top, don't you put your arms out like this? why do you put your arms out like that? little kids say to you, "hey, mister, is you balancing on the fence? how come you put your arms out?" so i put my arms out like this, kid, help me balance better. little kid says, "well, i can see that. how come holding your arms out helps you balance better?" and you say... [laughter] do you ever think about that? you guys know that's true.

i wonder if there's a reason for such a thing. and it turns out to-- that's chapter seven, okay? if i take a rifle and i hold a rifle straight out, i mean straight, put a carp in this level-- level, honey, okay? and i hold like that and i-- i fire a bullet, that bullet gonna go straight out, yeah? --hit the ground, huh? let's suppose when i do that, i drop a bullet from my hand. so one falls-- and it go straight out. now watch as when i do it again. which one hits the ground first? the one that's fired or the one that drops? take a guess and check your neighbor. oh, how about this, gang? how about i go like this? i fire--and i fire down and i-- when i hit? when i fired down, let go, which one hits the ground first? the one i fired or the one i dropped? try it. begins with an f.

all right. let's suppose now i aim it up in the air like this, all right? and i fire. and when i pull the trigger, i drop one. which one hits the ground first? the one that drops or the one-- begin with a d, try it. [laughter] look at that. dropped, all right? now let's suppose i go like this. bam. which one? fire. all right. like this then, lee. it didn't drop. oh, i fire, and when i fire, i'd let one drop. no tricks. which one hits the ground first? the one you just fired. okay. how about like this? bam. the one that you fired because it's tilting. yeah. how about like this, lee? the one that you dropped. ah. how about like this? down. how about like this? how about like this? that's hard to tell. can you see it's an even-steven and say they both hit the ground same-same? ain't that neat? we're gonna talk more about that. you're driving a truck, you slam on the brakes. you skid to a stop.

now you're driving on the same truck and you gotta load it up with 15 tons of pianos. you slam on the brakes. you skid to a stop. in which case do you skid further? the one without the pianos. you're in this roller-skating rink. in a roller-skating rink, you're skating around. all of a sudden, someone got a little piece of gum on the floor. you hit the gum, boom, you fall down. you get up, you're okay, 'cause you hit the wooden floor. okay? now you're outside, you're skating in the park, okay, on the concrete. there's an acorn on the ground, right? you're skating by it, whoop, boom, you fall down. somebody called over and they have to get a medic for you. what's the difference? why is it falling on the concrete, you get wiped out? you fall in the wooden floor, bounce a little bit, you're okay. why?

and you explain that to a little kid and you tell the little kid, when you hit the wooden floor, honey, when you hit the wooden floor, it gives a little bit. it bends down. but when you hit that concrete, it doesn't give. just like the difference between jumping out of a building into a net, which gives, and jumping onto the, you know, a concrete sidewalk, which doesn't give. which is better for you? or depending on the effect you want, okay? okay? but then you could say to a little kid, "hey, when you fall on the wooden floor, that little give, that helps you." and the little kid says, "well, i know that. "why is it that when you fall on things with give, "you don't get hurt? "and when you fall on things that don't have give, you get hurt?" hc. and you say-- do you guys see what the-- you getting the flavor? sometimes, physics takes simple questions and it finds out that the simple answers we have are only the beginning of an answer, and we gotta go a little deeper. and that's what we're gonna do. this whole course is all gonna be common sense.

stuff you already know but yet little bit deeper, oh, wow, it's a little bit more surprising 'cause you're looking a little more carefully. we're not talking about weirdo stuff. we're talking about the physics of the everyday world, the stuff that's around you all the time and all the stuff that's gonna start to make more sense to you, and you find that one thing links to another and things connect in a beautiful way. and you can answer little questions like that. and in answering those, those bring new questions, which bring more interesting answers. and it keeps going and going and going. then we talk about electricity. we'll talk about sound, musical sounds. electricity, 110 volts in your plug, huh? we'll have a great big van de graaff generator in here that'd be charged up to a million volts. a million volts. and you got 110 volts in your household circuit. if you take a couple of pieces of wire and stick them in your household circuit, that might be the last thing you ever do. but yet, you can come up and you can touch that million-volt generator. boom, high volt-- and you're okay. hc. how can be?

similar to that. you guys know that if you reach in and you touch a hot pizza oven-- you touch the hot oven, you're gonna get burned if you touch the inside, right? but can you put your hand on the hot pizza oven in the air without getting burned for a moment? yeah, you can do that. and it's just as hot as the side of the oven. do you know that? yeah? you guys know, too, that if you had a frying pan in there and it didn't have any handle and it had a iron handle, and you reached in, and that thing is like 400 degrees, you reach in and grab it, you know you're gonna be hurt. right? but you do know if it's a wooden handle, you won't? you can touch the wood, the wood get the same temperature. but you can grab the wood and take it out quickly without burning your hand. and that's because wood is different than iron. you know what it is? do you know what the property that's different is? have to do with heat, have to do with conduction. put them together, we call it, what-- hc, heat conduction, okay? and guess which has a poor, poor heat conductivity, wood or iron? begins with a w. try it. okay.

and you know what? even if the wood is hot, even if the wood is red hot-- you know about these people that have these little courses and they charge you 300 bucks and they teach you to walk barefoot on hot coals? right? mind over matter, and what kind of noodles you eat and all that sort of thing. it's straight physics. that wood is a good insulator even when it's red hot. why is that true? we'll be talking about that, things like that. you guys know these little fourth of july sparklers? see all that white stuff coming up? the white spark? do you know how hot those white sparks are? it's over 1,000 degrees. and you give this sparkler to a little kid? the little kids hold it like that, hey, fourth of july, honey. and these little sparks are bouncing all up to the kid's face. that's like 1,000-degree sparks. how come those 1,000-degree sparks don't burn up the kid?

same reason when you touch that van de graaff generator, that million volts, it ain't gonna burn you up either. why is that true? we're gonna talk about these ideas. we're gonna talk about the idea how energy relates to these things. it's the knowing how hot-- how much energy is gonna flow. and we get that idea. we make these distinctions. you guys know when you go on the top of the mountains, it's cold up there. but you're closer to the sun, right? in the top of the mountains, it's cold. and somebody say, "hey, how come it's so cold up here?" so--we're closer to the sun. wait, no, no, no. that should make us hotter. you guys know when you're approaching the sun, it gets hotter and hotter, don't you? have you known that? i mean, you can get in the best ceramic materials that the humans can make. you get within a million miles of that sun. honey, you're gonna fry to a crisp, a million miles from the sun, unless you go at nighttime. [laughter] hey, but the point, back again, you're up at the top of the hill and it's cool up there. and you know what you can tell your friends? hey, gang, you know why it's so cool up here? because warm air rises.

let me ask you a question, does warm air rise? you guys know about that from before? did you guys know that you get in the top of a ladder, you're painting the ceilings a lot harder up there than down below? warm air does rise, okay? why does warm air rise? evaporation. oh, there's probably no reason for that. it's just one of those things that happen, right? no, no, no, no. warm air does rise--and when warm air rises, when a volume of warm air rises, is there more pressure, more air pressure up there or less? less. when you're swimming in the water and you're way, way, way down deep, more water pressure or less? more. begins with a m. more, right? and as you come up, doesn't the pressure get less and less? right. well, guess who lives in an ocean of air, begin with u, end with us-- i mean, s. us, we live a ocean of air. and up there's not so much pressure. so let me ask you guys a question, what do you suppose would happen to the size of a balloon if you let it go and it floated higher and higher? would the balloon get bigger or get squashed up smaller and smaller? think about that and check your neighbor right now.

so what do we think, gang? what's gonna happen to the air? is it going to expand, they'll get compressed? expand. when you take a flat tire pump and you... you compress the air. do you heat up air or do you cool it up? - heat it up. - heat it. you guys get practical experience on that? no. what happens when you compress air? heat it or cool it, or-- well, i don't know? - compress. - how many say i don't know? show of hands. how many say you heat it up? - heat it up. - heat it up. how about the opposite? if you expand some air, does it heat up or cool down? would you like to have the answer to that? i could tell you the answer and you could put it in your notes. how about i show you the answer? everybody take their hand and put it in front of their face, right or left, either one. open your mouth, and blow on it, with your mouth open. hottish or coolish? hot. okay. now, that there didn't expand very much. now, do it again, and this time, make your lips down small

so the air has to expand when it comes out. try it. hey, hey. what happened to the expanding air, gang? what did it do? begin with a c or h? c. c, it cooled. how come the air cooled? that's chapter 17, okay? [laughter] you know how we answer a question like that? by thinking small, really, really small. we think down to the little atom. you guys know you're made out of atoms, don't you? i mean, not all of us, but most of us, right, okay? those who have the citizenship are made of atoms. no, no, i'm kidding. we're all made of little atoms, you guys know that? a lot of atoms or a little atoms? begin with a l. try it. lot, a lot of atoms. a lot or a lot lot? a lot lot. a lot lot. a lot lot. when you breathe in some air, atoms go in your lungs?

right? now when you breathe out, same atoms come out? well, if that's the case, then why would you use clorets, right? now, can a dog tell who you are by-- dog can tell even in the dark, yeah? when you breathe the atoms out, you're breathing some of those out-- the molecules now, right? you got--molecules, right? collection of atoms. now when you-- every time you breathe out, guess who's going outside? guess. yourself. part of you is going out, honey. a dog can pick it up, right? even some--"harry's home," you know? [laughter] yeah. it turns out, every time you breathe, you're breathing out a part of you. now when you're breathing out part of you, there's a part of you going all up through-- someone comes by-- now, what do they got? a part of you. and that becomes part of them. so you are a part of them. are they part of you? let's--"i don't want anyone else to be a part of me. i wanna be my own scene," right? you can't do it, 'cause every time you breathe in air, you're breathing atoms that were exhaled

by someone else. now, how many other people? we're gonna be learning things like this. hey, dig this. it turns out there are more atoms of gas in your air-- i mean, in your lungs than there are breaths of air in the whole atmosphere of the world, almost the same ratio, just about as many, 10 to the 22 in here, 10 to the 22 atoms? that's 10 with 22 zeros. and you got about 10 to the 22 breaths of air in the atmosphere. a little figuring out will tell you this that if you took a breath of air, and then-- now, wait six years when it's all spread out. and go to some other part of the world and go... guess what you got. you got, on the average, one of those atoms that was in that one breath. yeah? and there's many, many more breaths of air in your lungs than there were people that ever lived. people that ever lived, about 10 to the 10th. so every time you take a breath, gang, you are breathing people who came before you,

or even people that are alive six years ago on the other side of the world. so you know how these buddhist types say, "we are all one. we are all one, my children." what do the physics types say about that? - you're right? - it's true. it's true. we're all the same atom pool, cycling-- you wanna do a short story sometime? write about johnny atom or julie atom. okay. and how an atom goes from one place to another and goes da, da, da, da, da. and, you know, the atoms that make you up, guess how old they are. older than the sun or younger than the sun? older than the sun. the atoms that make you up were around before the sun came to be. how can be such a thing? and we talk about that. kind of powerful. then we're gonna talk about-- we're gonna talk about color. see that's blue. you can see that's yellow. you can see that's red. how come they're different colors?

somebody say, "hewitt, come on, we know that. we know that. "the white light up above. "the white lights, all the colors mishmash together. "that's what white light is. "red, orange, yellow, blue, blue--all smudged together. "and all as it happens, the white light's coming down, "this just reflecting the blue part, "this reflecting the red part, "that's reflecting the yellow part. big deal." you say, "yeah, i know. we know that." why does this reflect the blue part? why didn't this reflect the yellow part? and why does that reflect the yellow part? now, why not the red part? huh? what's going on? and to answer that, you gotta get down at the atomic level. why do things have colors? why is the sky blue? most of the time. how many people say, "oh, there's no reason for the blue sky. "the skies just happen to be blue. that's the way it is." there's a reason for the sky being blue. did you guys know that? and also, how about the red sunsets?

the sunsets turn orange, huh? you know what some people say at this point? "hewitt, off, man. leave me alone. "i don't wanna know anything "about little atoms making red sunsets. leave me my sunsets." some people think that if you explain the sunset, you're kinda spoiling it. you know what i'm saying? "i don't wanna know. "i don't know about that little optical tuning forks "and all that scattering and what's left-- i don't wanna know about that stuff." which then tells you--that can tell you why a cloud is white, and tells you why the water is the color it is off of white here, sort of that greenish blue. why? here's my bias, gang. to understand more about these things is to appreciate more about these things. now that's a bias. i could be wrong. and that's individual. i'll give you an example. the person who appreciates music most is a person who understands music, who knows what to listen for. and i think, too, the person who can appreciate the world most is the person who understands most what's going on.

what i'm gonna be doing in this course is not telling you how beautiful the world is. i'm gonna be telling you what to look for. and when you look for things, you'll see that, "hey, that's a beauty," that you would've-- wouldn't have noticed otherwise. so we're talking things like that. and then we're gonna talk a little bit about nuclear physics: fission, fusion, radioactivity. what do you suppose makes the earth hot? volcanoes. where's all that heat coming from? would you believe it's nuclear power? nuclear power under the ground? would you believe it's radioactive decay? you know, if this were a piece of uranium, this piece of uranium will be a little bit warmer than anything else in the room. you know why? it's shooting out these little particles all the time, heating it up. and if i make it very, very enriched with uranium, it's gonna be hotter, hotter, hotter. and guess what we get about from the bottom of the world.

so people that are afraid of radioactivity and nuclear power think it's something new that the human race has just come up with. nuclear power has been around before the sun was here. that's what keeps the sun and the stars hot, and that's even what keeps the earth hot. how come the earth hasn't cooled off by now? because there's radioactive decay happening underneath. now we're gonna be talking about that. and that's particularly relevant here in hawaii, because what--well, we got that hot, hot, hot spot. what makes that hot spot hot? what's fueling it? is it like a carbon and oxygen combining? no. it's at the nuclear level. and most of everything we're gonna talk about is gonna be like physics of the everyday world like that, but we are gonna get far out, and we're gonna talk about the ideas of albert einstein, the ideas of relativity. what time it is on your clock and how you move through space are related. did you guys know that? we're all sitting at rest right now, and our clocks are running.

we are advancing into the future at all the same rate. we're in the same space and we all share the same time. but when i start to move, my watch is running differently than your watch. so long as i'm moving, it doesn't go at the same pace that yours is. now, i'm only moving a little bit. and so the change is only a little bit. so little there's no way that we have no instruments to measure the change for that kind of speed you saw. but if i start goosing that speed up faster and faster and faster, that difference in time becomes more apparent. you heard about the twin paradox, a couple of twins sitting? one twin sitting over here, one sitting in a rocket ship... takes off, goes off... travels at speeds, you know, the speed of light? comes back down, still young, and the other twin over here-- so the one that travels doesn't age as fast as the one that stays behind. is that true or not? begin with a t. true.

take a piece of radioactive mineral, make it whirl round and round and round, now measure it, and the decay rate goes down. stop it, flip, then, same old decay rate. so when you're moving, the rate at which time travels changes. so does that mean if you wanna be young, you should do a lot of marathon and stuff? you notice i keep walking back and forth like this. [laughter] so you should never sit down... never sit down. keep on trucking, honey. that's where it's at. yeah. so if you keep on running marathons-- marathons, you'll never age. oh, really? now i'm kidding a little bit here, okay? the effect is so small that it's completely escaped the notice of the human race except one particular person, and that's a person who was thought to be a mental retard when he was a kid. that's a person who didn't talk till the age of four. that's a person that took algebra in high school and couldn't hack it. come on. some people can hack it, some people can't hack it. it's okay. you don't have to pass algebra. and he couldn't pass his algebra. who am i talking about? in fact, he didn't even get a high school diploma.

no. then he want to take the entrance exams to get into the polytechnic institute, and guess what he did, begin with a f-l-u. he flunked. that's okay. some people pass, some people flunk. don't make a big deal of it. then he met someone, got him-- tried it again, this time, he passed. and he did very, very well in school, it turns out, and we're talking about who? albert einstein. some people's time is a little bit different than other people's time. some of you people sitting in the class right now, it's the wrong time for you to be here. it really is. maybe a little bit down the road, all the stuff we're gonna talk about will more resonate with who you are. sometimes, information comes in at a time when you're not ready for it. it's kind of a shame. and sometimes it comes at just the right time. and information comes in when you're ready for it and you grow, you grow, you grow. it's like watering a plant. you gotta water the plant at the right time. and here we are all in class and we're gonna all learn physics together, and i hope, for all of us, it's what? it's the right-- the right time, huh?

this is the time to learn about the physical world. i want you all to do something between now and next time. we're all gonna look at chapter two. we're gonna be reading about it. we're gonna be reading about motion, moving things, accelerating things, falling things. and we read about that, and next time we'll talk about it and kind of pull it all together. okay? catch you next time. physics. [music]