of about 40 millions joules per liter. 40 million. now, this is what the energy thing means. if you have 40 million units of energy to spend, that's the energy content in your gasoline. what we're saying is these two numbers multiplied together can't be bigger than that 'cause that's what you got to spend in your gas tank. i don't care what kind of gadgets you got. that's it. now, how are you gonna do it? you're gonna push your car through some distance. let's see how far you can push it. how far can you push it? well, if you're pushing it uphill, it's gonna take more force, so this must be smaller. pushing it downhill, maybe gravity will do it for you, you don't even need anything, okay? but along a level road, you gotta push against the air drag. isn't that true? the fast you go on an air drag-- and let's take an average unit of a thousand newtons,

a thousand newtons for our force. and now, we wanna calculate. can we calculate, gang, at our sits, huh? pencil and paper. what's the distance that the car could go with a thousand units of force pushing along? how many kilometers will the car go on that one liter? calculate such thing now. am i doing it right, gang? right. yeah. am i doing it right? yeah. if this times this equals that, then this equals that divided by this, is that right? is that the algebra? we can do that? look at the zeroes, honey. now, anyone have a calculator?

how about without a calculator, we can do, huh? one goes in the 40,000 how many times? 40,000. so this car is gonna go 40,000 meters. and it turns out, if we express force in newtons distance in meters and energy in joules, the units will match. so we have no conversions to make. so this turns out to be 40,000 meters. we don't say 40,000 meters, we say 40 kilometers. so it turns out to be 40 kilometers. you know what this means, gang? in a car that is 100% efficient, you can't have that. make believe you can. 100% efficient, that means all the energy of the gasoline goes in the moving the car. nothing goes into the heat, nothing goes into the sound, nothing goes into the friction, huh? all into the car, there's a upper limit. if you have to push with 1,000 newtons, which is--was it reasonable-- then the greatest distance you can possibly get,

nature's ultimate, is 40 kilometers. so this car will give you 40 kilometers per liter. and there's only one way you can get more. how's that? what is that? this is--huh? how can you get more distance? you go outside of your car and you push on it-- by changing the force, that's right. if you can decrease the force, then you can increase the distance. do you see that? and how do we decrease the force with cars? -- we make them streamlined. so they cut through less air drag as they move. isn't that nice? see? and usually, you're gonna get about 25% efficiency, which means you'll get 25% of this. okay? which means you usually get about 10 kilometers per liter. see? yeah. yeah. so what you're trying to do is to increase the efficiency. but this is in the upper limit. see? now, most people don't realize this. people don't know there's an upper limit, that nature's limit. and they think that little gadgets or something can how-- somehow beat this.

and many of the devices that are submitted to the patent office float this all together. and the first thing that patent types do with some particular machine, they say, "wait a minute, is it gonna violate "the conservation of energy? if it does, we don't wanna look at it." and the reason is, the patent people have looked through thousands and thousands and thousands of scheme, maybe hundreds and hundreds and hundreds of schemes, which all seem to give you out more energy than before and they find out where the little flaw is. so at this point, they just say, "look, if it violates energy conservation, come on, it's another wacko-wacko." because nothing has so far shown that you could get more out than you put in. so there are rules to the universe, and that's one, energy conservation. you can change from one form to another, but you can't get more than you started with. no free lunch day. and with most machines, you don't even break even 'cause some of that energy goes into overcoming friction, turns into heat.

so why do you eat your cornflakes in the morning, gang? you eat your cornflakes in the morning, what do you do? those things are being torn apart in your stomach. and they're torn apart, the bonds, that energy becomes part of guess who? and you use that to go about your day. and what happens if you stop eating? how long can you keep running a car without putting gasoline in? how long can you keep running your body engine without putting food in? so the conservation of energy, hey, biology right underneath it. here's a neat little device here. it's a generator. consists of magnets, these magnets, and inside here, i have a coil of wire. and i'm gonna turn that coil of wire, and the coil of wire is gonna turn inside the region called the magnetic field. and when it does that, it's gonna induce electricity.

and when i do that, i can light the lamp. how that happens, we'll talk about later in the course. but for now, we can look at this in terms of energy. that light that you saw glowing, that's a form of energy. what was the source of that energy? it was the cornflakes i ate this morning. because it takes-- i have to work on this to turn it. see that? and if i wanna make it brighter, i gotta work more. isn't that neat? okay. later, we'll learn that if someone could keep turning this thing, we could generate electricity to light up cities. and sure enough, we do. and we have devices like this. and we put a waterfall over here and turn it, use the energy of that waterfall, potential, kinetic, rotational, mechanical, off it goes this light, huh? do that, or we could put a steam turbine here, direct some expanding steam against the turbine, against the paddle wheel and turn it.

and so our civilization really rests on devices like this. but there's gotta be some energy input to be transformed over here. now, here's a neat little thing. when i turn this and i unscrew the lamp, it becomes easier to turn. easier to turn. why? well, when it's unhooked, there's no energy going off. and so what i'm turning against now is a friction. but when it's hooked up, i'm pushing against the friction plus the electricity. so let's--i can show you that. can i have a volunteer? could you come up here, please? what i'm gonna do-- you stand over here, and what i want you to do-- i'm not gonna look, i'm gonna look over here, okay? and i want you to unscrew that, and i'll tell you when it's unscrewed 'cause i'll feel the difference over here. so let's tighten it up now. okay. i'm gonna do it. okay.

is it unscrewed? do it again. now it's on. off. how do i know? i'm looking at a mirror right up here. no. but you see that? you try it. you try it. -- can you feel it easier? yeah. do it, go ahead. see if it gets harder. okay. keep a nice steady cadence. yeah. i can see the mirror. oh, yeah? no, never mind the mirror. okay. okay, here we go. go ahead. go ahead. now this. now, how about now? harder? harder. okay. easier. it's gone. nice, huh? huh? huh? okay. okay. the handle knows whether the lamp is on. ooh. how about that? what's going on there, gang?

even why that happens, the mechanics of why that happens, we're gonna get up to when we get up to electricity and magnetism. delicious stuff. okay? but we see that energy, concern. the energy i put in, the energy come out. okay? right there. much easier to turn. try it after class yourself. it takes energy to light the lamp. that being the case, let me ask you a question. you get your car. you wanna find out what your gas mileage is 'cause you wanna compare it with your friend's cars. you all got a contest. this friend is bragging up about getting so much mileage, that so much mileage. you wanna test yours too. so you're driving your car and you're driving along the highway, you're looking at the speedometer to see how miles you go, tank it up later on to see how much gas, divide one to the other, you see how many miles per gallon you got, how many kilometers per liter, yeah? and you're doing that and you're driving along,

and as you're doing that someone reaches over and turns on the radio and pulls out the light switch and pushes in a cigarette lighter. and you say, "would you cut that out? you're screwing up my gas mileage." true or false? it's true. check your neighbor. -- what's the answer, gang? begin with f. false. end with alse. or begin with t ends with rue. yeah. true. which one? true. how many say, true? how many say, hey, when you're driving at nighttime, if you wanna save on gas, what should you do? switch your lights off. [laughter] people say, "how come you're driving with no lights?" "i'm trying to save gas." true or false? true. now, true. that's right. so i want you guys to all learn something in this course. i don't want you driving at night with your lights on. drive with your lights off, right? [laughter] no, we--maybe it's worth to burn a little more gasoline to keep from crunching up, huh?

but nevertheless, you are burning more gasoline when you put your lights on. see if your friends know that. now, a lot or a little? answer begins with an l. probably a little, okay. probably a little. but you really are. there's no free lunch. how about your aircond in your car, your air conditioner? when you put the aircon on, does it burn more gas? oh, yeah. somebody say, "oh, the aircon. "just hook it, i mean, to the belt, "i mean, it spins. i think that's just hooked down to the drive--anyway." --drive if you have turned the hook on. i mean, that doesn't know the difference. it doesn't know the difference? did this know the difference when this was on? it knows the difference. it's got to push, it's got to do work. you're gonna burn a lot more gas with your air conditioner on. you know why? especially on a hot, hot day, because now you're having to put out more energy to get to air condition the car, more energy. how we do that? we're gonna be talking about later, okay? talk about that too. ain't that nice? a whole a lot of ideas we can talk about,

'cause all these ideas begin with f. what are they? physics. physics. physics, that's right, yeah. let's talk a little bit about kinetic energy. i haven't given you the relationship for kinetic energy, yet. let me give it to you. it's a little tricky. i'm not going to derive it. it's derived in the footnote in your text. i'll just state it without proof. it's half a mass, multiplied by the speed square. remember momentum was just mass times speed, simple, simple. this, somewhat more complex, because it's half the mass times the speed square. the square of the speed tells you that, wow, it really depends on speed, because it's speed

multiplied by speed. so it's very, very speed dependent. when we talked about firing the rifle before, the momentum of the bullet equal the momentum of the rifle coming back, so momentum, momentum, same. impulse, impulse, same. but that was kind of bothersome to some people 'cause this has got something more than this. and you know what it has more of? energy, okay? because the--had a bigger speed. but now, with energy, it's squared. so the bullet going out might have the same momentum as the gun coming back. but honey, most of the energy is in the bullet, not the gun 'cause we're squaring that greater speed. you square the speed, the results-- i'll give you an example. you're driving down the road in your car

and you're going 30 kilometers per hour. and you, you step on the breaks, you screech to a stop. you're gonna change your kinetic energy. you're gonna change it from the kinetic energy you have at 30 kilometers per hour down to zero. what's it take to change that kinetic energy, gang? it takes work. and that work is what? what kind of work stops your car? we can let the equation guide our thinking. it's a force and it's a distance. distance is the distance your car skids, yeah? and the force must be the friction force of the wheels against the road, yeah? okay? yeah, i mean, the-- yeah, between the wheels and the road, okay? so that's the friction force, that's the distance, okay? so you-- [makes noise] let's suppose you skid 10 meters. ten meters. now, we repeat. we go twice as fast. we get twice the momentum, yeah? we go twice as fast, we step on the breaks, we skid to a stop. we skid further.

some people will say, "well, twice as fast, you're gonna skid twice as far." tilt. not twice as far. how much far? check the neighbor. see if the neighbor knows already. twice as fast, gang. how many say twice as far? how many say more than twice as far? how many can calculate it to be f-o-u-- r. --r, four times as much. so you're gonna skid-- if you got four times the energy, you're gonna skid-- four. --four times as far. it turns out the friction force won't change to its speed. how much the tires in the road grab each other does not have to do with speed. see? so you got the same friction. now, the same friction is gonna drag you four times as far. that's why people go on a little bit-- when you first learn to drive, you've got to pick this up savvy-wise, you know? you go a little bit faster. you step on the breaks and surprising it for--

wow, it took so much longer to stop. or you boost that car up to three times as fast now, three times a speed, okay? so not 30, not 60, but 90 kilometers per hour. now, with three times a speed, you know you got more energy, more kinetic energy. some people know how much more, check with the neighbor. how many say nine times as much energy? that means you're gonna skid how much further? nine times as far. that's right. do you get the idea? so kinetic energy is velocity dependent squared. drop a ball, gang. when i drop the ball, it'll never return to the same height. why? potential, kinetic potential, but there's a little gap. what's the gap in potential energy? where's that energy going, huh? heat.

it's going to heat. it's gonna warm up the table, warm up that ball. so you never can get a ball that will bounce as high. almost, but not quite. here's a little device that's kind of nice. it's a portion of a rocket ball and i can invert it. when i do that, am i giving it a little energy? i'm gonna drop this and watch. did you see that? it bounced higher than when i dropped it. hc? and here's another question, too. will it always bounce higher from where i drop it? if i got higher up, would it still bounce higher? where is the point where it will not bounce higher anymore and why? think about that. good physics, yeah? i'll show you another idea with energy. here's a super ball. the super ball, i'm gonna let it go-- some people think a super ball will come up to the same height, but it won't. it comes up to about a little bit more than half height, okay? this super ball is guaranteed to give a thousand bounces. we got this this morning. troy's been pulling it.

troy, how many bounces did you get on it? 995. 995, okay? there's 96, 97, 98. okay, let's see. 999, 1,000. sure enough. that's true. let's try it again. a thousand. its elasticity is gone, gang. [laughter] think about that. catch you later, physics. [music]

i'm dr. john simmons and i'd like to invite you and welcome you to another session of beliefs and believers. we should have a fascinating class here, looking at the religious process. but we crossed over some themes last time, particular identity