okay, gang. let's begin. today, we're gonna talk about rotational inertia, rotational inertia of rotating things. before we talk about the idea that acceleration is proportional to force, remember that? double the force on something, you double the acceleration, there is a relationship between the two.

now, we're gonna talk about rotational acceleration. and rotational acceleration, we're gonna call it "a", but a greek letter "a". we call it like this. rotational acceleration is proportional not to a force, but to something else, begin with a "t". see if you know? rhymes with who you're sitting next to, try it. how many still will not be seeing it? it's torque, gang, torque, okay? rotational acceleration is proportional to torque, and i write a "t" like that, it's a greek letter, "tao." why we do that is because in advanced physics books, you get those symbols, and we might as well all talk the same language. so all we're saying now is if you want something to rotationally accelerate, you apply a torque to it. remember the torque will make things spin, a twisting force and that's all we are saying here. but remember something else too that how much acceleration you get depended not only on force but something else.

and see if your neighbor doesn't know what the something else is. not only how hard you push, but da-da-la-la-la-la-la. check your neighbor "a". how many say it begins with an "m"? all right, let me give you a hint. rhymes, it starts with "m" ends with... [laughter] what is it gang? mass, mass. you hear me? okay, come on, we know that. come on, don't be shy. in fact, if we put the correct units in, we can say acceleration is equal to those two. it's equal to the ratio of force to mass. we talked about this before. now we're talking about something analogous, something very similar. we're saying that rotational acceleration depends upon the torque, but also on not just the mass, it has to do with its whole inertia and the inertia to rotation is different than the inertia

for just back and forth motion. so instead of saying mass, we say inertia and i use a capital "i". and if i put proper units in, i can call it an exact equation. so how much rotational acceleration you're gonna get something to pick up, huh? will depend upon how much torque you put on it, but how much rotational inertia does that something have. it turns out that rotational inertia is complicated. and we're just gonna get the idea of it today. rotational inertia is mr2, the mass multiplied by the distance from the rotational axis when the mass is localized. ordinarily, for different shapes, it's a more complicated equation and we won't get into that, but i can kinda show you that with this idea. here i've got a couple of plastic pipes and in these pipes, i've got some lead.

and i'll tell you, the same amount of lead in each one. could i have a helper, please? my helper today gang, this is tinnie lim. she is the lady in that energy chapter who is pulling the bow and arrow back. tinnie was my student at city college in san francisco in 1980. got into conceptual physics, it spurred her on. today, she is a design engineer at jet propulsion labs in california at pasadena, and she is working on these fly-by missions and all that stuff and right now she is doing what, you are making a pod to fly in the next space shuttle, and that's what she is doing, okay? tinnie, hold these up and then tell me which of those two has the most mass? they feel the same to me. these are the same weight gang, okay? but i want you to do something else tinnie. i want you to hold it at the midpoint, and then rotate it like this. and now try this one. any difference? this is hard to rotate. very much hard. take them both and do it.

like something up here? yeah, you can really feel the difference. let's try this. put this in your hand, flip that like this, you do like this, flip it. okay, now change gang, now change. oh-oh-oh-oh huh? guess how the lead is distributed inside here, thanks very much, tinnie. guess how the lead is distributed, gang. guess where it's closer to the center. take a guess. they're both the same heaviness. they have the same mass, try these. try this one. you see any difference? same mass, but different rotational inertia. rotational inertia is different, because in one case, when we hold them at the center. if the mass is out on the ends, it's hard to rotate. if the mass is inside, what's "r" become?

close to zero, and so the rotational inertia becomes very very little. so the further away the weight is, the harder it is to get going. here is a hammer. i balance the hammer with a couple of fingers like this. that's not too difficult. [laughter] but, if i go like this, you try that. right, next to him, all right. okay, try like that. now try it with the other way. any difference? harder this way? is that right? harder this way? strange. see this way. well, no, no, no. what did it really feel like? look, if i turn this through 10 degrees, the mass doesn't have to turn very much.

but how about if i turn it through 10 degrees like this? the mass has a far distance to go. it's much more stable like this than it is, like this. -- let's try this. tinnie, try this one. try balancing it with a couple of fingers right here. you guys protect yourselves. okay, couple of fingers, yeah. now balance it as best you can. oops, let's try it like this. it's easier this way. easier, yeah. it's a lot easier to balance something like this with the mass this far away. when the mass is far away, the radial distance of that mass to the pivot point is big and the bigger that radial distance, the greater the rotational inertia. now that's kind of complicated gang. i = mr2.

we're saying the inertial rotation have to do not only the mass, but where it is. when it's far away, more rotational inertia, more lazy, more tendency to just stay right there where it is. you see those dudes at the circus going like this, and they get all the friends up on the top there and they're balancing all their friends who are doing cartwheels and spinning plates and all that jazz, right? and people look up, they're saying, "wow, man, how did that guy balance all those people?" well truth be told. it would be a real feat if he did that and held an empty pole up like this. that would be difficult. putting all his friends up at the top, the guy can take a nap. they get so much rotational inertia, they are not bound to move very much, so more stable when the load is far away. make sense? when you make a flywheel, the best flywheels are the ones with all the masses out at the edge of the rim.

and that flywheel when you get that sucker going, take a lot of torque to get it going, but once that's going honey, that's gonna keep on going. and you can drive machines and do all sorts of things, the flywheel in your car keeps the driveshaft going in between firings and the more rotational inertia of the flywheel, the more it tends to keep going, going, going, when you want it to. rotational inertia depends upon distance from the axis of rotation. okay gang, i've got something nice for you. it's a couple of sticks. i am gonna take these sticks and gonna pop them against the book, stick like this, a stick like this and i'm gonna drop them. i'm gonna let the two sticks drop and you tell me, which stick will hit the ground first. ahh, place your bets, place your bets, which one gang? the one with the clay at the top or the regular one? check your neighbor.

okay, let's try gang? here we go, 1, 2, 3... ooh, rotational inertia, yeah? you like that, huh? all right. if you understand that, if you do, you can answer this question. here is a pendulum. i am going to swing the pendulum to and fro. i have a relatively large radial distance that's from here down to here. i'm going to swing it to and fro and you watch it. it has a rotational inertia. it's a little bit lazy. it doesn't do that tit-tit-tit-tit-tit. it does it rather at this particular pace. what i'm gonna do now gang, now that i have you under my control, i'm gonna shorten the string. and when i shorten the string, ask your neighbor, "will that change the rotational inertia, it don't change the mass?" does it change the rotational inertia? does it make it more inertial or less inertial?

neighbor. now i am going to swing it back and forth, gang. more often or less often, check the neighbor. you see if we know a little bit of physics, we can predict things. and if you've been understanding this stuff we talked about, you can predict things. to and fro at a faster pace or at the same pace or less pace? how many say, a faster pace because now there is less rotational inertia, but the same mass, show your hands. how many say, "well, i don't know. "i'll kinda just wait and see whatever happens, you know, i will keep notes, and i am just going for a 'c' anyway." show your hands. how many say, "no, it seems to me if you make the string short, the rotational inertia will get greater." you say, why greater? well, i know a lot of things that i expect always turn out the opposite way. let's try it gang, look at this.

okay, and like this, less rotational inertia, then you got tit-tit-- you see people walking. when you walk, don't you walk at a pendulum rate? don't you allow your legs to swing like a pendulum? isn't that true? and if you've got long legs, you've got a lot of rotational inertia or a little, long legs? long lazy legs. did you ever see those texans walk around? the phomp phomp phomp the long legs phomp phomp phomp, little short girlfriend it-tit-tit-tit-tit-tit-tit-tit. okay, that's physics. we see some people think, oh that little girl, man, she gotta take quicker steps to keep up. no, no, no, no, she takes quicker steps even when she is not keeping up with him, huh. how you walk, how you swing your legs, hey, it's physics, okay? long-legged things, take long lazy strides. why? because long-legged things have more rotational inertia. short-legged things have less rotational inertia. swing back and forth more quickly like this pendulum.

look here, longer. so there is physics in everything around is, gang yeah? kinda neat. when you wanna pick up speed when you're re running, you bend your legs. everybody know you bend your legs, you even bend your arms to go back and forth faster. check your neighbor and see if your neighbor knows why it is that you bend your legs and make them shorter when you wanna run faster, go. how about it gang? why do you bend your legs? some people say, "well, if you bend your legs, "there will be less rotational inertia. "less rotational inertia easy to swing back and forth. i see it, i see it, i see it." who see it like that? let me see the hands. yeh-hey, my people, tinnie says all right. all right. you're walking along the railroad tracks with your friends. railroad tracks, you guys don't know how railway tracks around here. let's guess, you're walking along the top of a fence.

no railroad tracks in hawaii, right except on the beach. anyway, you're walking along the top of a fence with your friends and you've got your hands out like this. little kid sees you with the hands out. you don't walk like this, not if it's a high fence. okay. you walk like this, huh? little kids see you do that and little kid say, "how come you've got your hands out?" and you say, "to help me balance." and little kid says, "well, i know that. how come holding your hands out helps you balance?" and you say, like you say to your friend right now, especially if you're holding a couple of weights like this honey. like this, you could just take a nap. and you've got so much rotational inertia, you're not going to rotate, you see. you've got the mass. you're extending your mass out. you are increasing your rotational inertia. to increase your rotational inertia is to decrease your tendency to change your rotation. so if you're not rotating, how come this tight rope walker has a long pole? what's that long pole about?

that increases the rotational inertia of the tight rope walker. without the pole, how about like this? very hard to balance because you can rotate very easily, but spread out, okay, harder to rotate, get a long pole, even harder to rotate. it's harder to change your rotational state, the more rotational inertia you have. makes sense, okay? that being the case, you guys can predict this. i have a little piece of wood here. i have another piece of wood. i'm gonna put these pieces of wood together like this. and i'm gonna roll the wood down the incline. and i'll make a count, okay? and we will compare how fast it rolls now compared to how fast it will roll when i change it, okay? 1, 2... [laughter] let's try it again, gang. okay, here we go. now i am gonna count out and we'll see how long it takes

to get down those the bottom. 1, 2, 3... say about three. okay. let's try it again. this time, i am gonna change the mass. i'm gonna put the mass over here. no, i'm not changing the mass, i'm changing the configuration of the mass. because i think you see if you put this in the bathroom scale, it would weigh the same, yeah? but now i am gonna put it like this, and i am gonna rotate it. now before it took 1, 2, 3 to get down right? this time it's gonna take 1, 2, 3, 4 or 1, 2. it's the same mass, but a different rotational inertia for the same mass. check the neighbor to be sure that you're on to what we're talking about. you ought to get this right, go. roll down faster or slower? okay gang. how many say, "oh, i think it will roll down faster now, "because it got more rotational inertia. it's more lazy."

now wait a minute, wait a minute. don't get so mixed up, eh, faster or slower? slower. how many say, slower? almost everybody, almost. okay. it's okay. it's okay. here we go, gang. 1, 2, 3, 4... it was slower. huh--how come? and you know how come because it's stretched out, the mass is further away from the axis of rotation, not all of it, but some of it. and if you make some of it further away, it's gonna increase the inertia, not the linear inertia back and forth, but the rotational. hey, come on, all makes sense, doesn't it? how many more examples do we need to get the point? we got the point already, huh? enough said, get it, boom.

that being the case then, maybe a little redundant, but just to be sure, same same, mass. okay? same amount of mass. so we'd say if they have the same mass, same inertia, how about rotational inertia? these things are gonna roll down the hill. they're gonna rotate about their centers. it's gonna roll down the hill. it's gonna rotate about its center. same mass, same inertia, but different rotational inertias. see, if you're sittin' next to someone who knows which one is gonna roll faster, when i release them both at the same time? okay gang, how about i say this, "i ain't gonna show you." i will show you after the exam next month, fair enough?

how many say you know what i kinda would feel a little more secure if you showed me? i have thought it out, don't get me wrong, i am not one of these types that you're talking about sometimes, i have thought it out. but i still like to kinda confirm my hypothesis, please, please do it, please show me. show your hands. no, nobody need to see. all right no problem, all right. i ain't gonna show you. i will tell you what, 5 cents each, 5 cents each. give me a nickel each and i'll show you. get your nickels out, come on. this is probably the least part of your educational expense. come on, everyone get a nickel out. and those that don't pay have to go in the other room. go join the couch potatoes, we're going to turn the tv camera on. how about you guys in the other room, which one is gonna win?

gee, they are kind of reticent back there, huh? how about it gang? you wanna see it? is it worth a nickel? i will just collect the nickel after class, all right? if you don't want to pay, close your yes. how many say, "hey, honey, it's physics, i wanna be seeing all the physics i can see." here we go. yeah, did it come out the way you expected, did it? that's because you're learning physics. all right? now we have down here a rotating platform. do you see this platform, gang? it's a very low-friction rotating platform. what i'm going to do is i am going to stand on that platform, i'm gonna hold these weights out. when i hold these weights out like this, i am gonna spin like this. when i hold them out far, do i have a lot of rotational inertia or a little? a lot. how about when i pull them in? a little?

so if i get here, rotating like this and i hold them out, what happens when i pull them in? ooh, easier to rotate gang, harder to rotate. easier to rotate. woo-woo, okay. you see such a thing, all right. you go to the yahoo a little-- you go to the ice follies, you see the skaters turning around like that, they're spinning, spinning, spinning, spinning and when they're spinning, they pulled in like this, yeah? go fast, fast, fast, fast, fast and then they become on, da-ta-da-da... people think they are going like that for applause. you know what they are doing? you're trying to save them from breaking their necks. you increase your rotation, isn't that neat? so we can really see, you can try this after class. you can get to try it to really appreciate it. see that, yeah. there is another concept here, gang. it's called angular momentum. remember before we talked about liner momentum, okay? there is a counterpart here.

let's see what we mean before we talked about regular momentum. and momentum was just simply mass times velocity. now we're talking about angular momentum, the rotating, rotational momentum if you want. i'll abbreviate it, okay? and now it turns out to be, not mass but what? rotational inertia and not v in meters per second, but the speed in rpms. and the speed in rpms, we don't call v, little advanced now, we call it omega. i x omega. omega is rpms. rpms are different than meters per second, let me show you what i mean.

someone got a couple of pennies? a couple of dimes would be worth an "a". what i'm gonna do gang, if this is a merry-go-round and some kids are on the merry-go-round. and one kid sits very near the center and the other kid sits near the far edge. as the merry-go-round turns, which kid is going faster, the one in the center or the far edge? how many say, oh they've got the same speed. if they're gonna fall off the horse, equal for both and what's the answer? no. you can see the monitor back here, if you wanna look at it, gang. see the one on the inside. now it turns out they do have the same rpms, rotations per minute, but the one on the outside is traveling faster in meters per second, okay? and if we keep going faster and faster, guess which one will finally fly off, the one on the outside. isn't that neat? thanks, man.

let me give it, a lot of relationships today. let me give just the relationship for that rpms. the relationship between this and this is the speed you have on that merry-go-round, how fast the wind goes by your hair, has to do with how far away you are from the center, the radial distance from the center multiplied by the rpm rate. do you know what that means? to say that v = r omega, is to say, as you make the radial distance bigger and bigger, what's your speed? ever go ice-skating, you're all skating, and someone acts as the pivot point and everyone else skates around him, how about tail-end charlie. tail-end charlie are going the same angular rate, okay, if the line stays stiff, huh? but the guy on the end of hand is going through the air fastest because r is bigger. omega being constant, a constant omega, omega's rpms,

the angle swept down, you see. every part of my hand is going the same angular speed, but the tip of my hand, how flyswatter, huh? how come you can hit a fly with a flyswatter? you can't hit a fly with your bare hand. because that flyswatter gives you what, a bigger v for the same angular motion and so that comes down so fast, the fly can't get out of the way on time. so, how fast you go, has to do with how far away you are from the center when you have a particular angular speed. this is angular speed. that's distance from the center. that's how fast you're going. so we saw the dime on the edge had the higher speed. but here we saw, when i rotated around, around and around, i had a certain angular momentum when i started. when i got on, i had a certain angular momentum. i had a certain "i", which was kind of big by the way. when i held those weights out like that, the "i" was big. my resistance to rotation was huge, out like this, okay? harder to get me going maybe, okay?

but there i went and i went at a particular rpm. no external torque acted. no one came up and messed with me, i just pulled them in myself, all internal. so that means the momentum after gonna be the same. we talked about that concept before. we said, if an object is here and another object comes in, and one hits the other, phoom. and you don't mess with it from the outside, that whatever momentum you have before the interaction, phoom. after the interaction, you've got what? you've got the same momentum, but maybe redistributed. remember that? we call that the conservation of liner momentum, linear meaning straight line. now we find out in physics that there is a rotational counterpart. if you've got something rotating, calculate its angular momentum. let anything happen, so long as there is not something messing up from the outside, phoom, that angular momentum gonna be the same afterwards. and so when i spun faster, i mean, when i decreased my rotational inertia,

when i pulled in my "i", what would have to happen to omega? can you see it? and that's what you saw. and guess what gang, this times this, this times this, same-same. one of the things we do in physics is we think critically. and to think critically is to be able to distinguish between closely related ideas. some people say, "oh that's when the course gets tricky. well, let's look and see. i am gonna do something, and i am gonna ask you a question. and when you answer the question, be sure that your answer is to the question i asked and maybe not some related question that i didn't ask, okay? i am gonna get on here again and i am gonna whip around. i am gonna pull my hands in, and now back and go up.

how many people saw that when i pulled my hands in, there was an increase in my angular momentum. and when i put my hands out, there was a decrease in my angular momentum. check your neighbor. okay gang, how many say, "you know what? i saw some changes honey, but i didn't see any change in your angular momentum. it was the same everything you did." show your hands. all right, all right. now, let me do it again and ask another question. when i pull them in, how many see an increase in angular speed? well, how many didn't see any increase in speed? stand up, i want to see what you look like. come on, i almost broke my neck. you saw me speed up, but you didn't see the angular momentum increase. so the angular momentum, you don't see. you have to figure.

angular momentum get two ideas going. how much inertia which is most out like this, yeah, and how much rotational spin? two ideas at one time. now how many people do you know that can keep two ideas at one time in their head? you have to be able to do that to take physics, okay? do we see that gang? here is a question for you. some people say that when the polar icecaps melt, that it will affect the rotation of the earth. we rotate now once every 24 hours, and so we call that one day. some people say, if the polar icecaps melt, that 24 hours will be a little bit different than 24 hours because they think that when the polar icecaps up there melt, that they'll kind of spread out. what do you think? here are the polar icecaps up there

and they melt and they spread out. what's gonna happen to the length of the day? check your neighbor. l right, gang, the mississippi river, mississippi river got a lot of dirt up there, and that dirt all flow southward and as it flow southward, what happens to the length of the day, to new orleans, okay? hey, so what? it turns out, the distribution of the earth, if we change the rotational inertia, what will happen to the spin rate? it will change also, decrease one, you increase the other, ain't that neat? so you've got a whole lot of stars out there, and all these stars are all coming. they are slightly, slightly rotating, okay? and as they rotate, they gravitationally come in, and they get closer and closer and closer. now what do you suppose happens to the rotation rate of this new galaxy being formed

as these stars all start to get closer to one another, take a guess. what's going to happen to the rotation rate? spread right out into a nice big disk honey and that's the way it is. so when you look out at astronomy, astronomers all the time interested in angular momentum because they know what's concerned. whatever angular momentum a galaxy has at one time, it will have that same angular momentum at another time, but if it's tighter and the "i" is smaller, then the speed will be greater. it works, gang. it's the rules of the universe everywhere. so we see a little sample of it right here. question time. i've got here some water.

i've got some water here gang. i get the water in the bucket. you guys know what i am going to be doing with this water in the bucket, because we're talking about centripetal/centrifugal force, aren't we, right? i'm going to take this water in the bucket, what am i going to do? i am gonna go righup my head. and if get to the head top, i'm going to stop, right? no, i ain't gonna stop, okay? nor that i could help it. i'll just go, okay maybe towards you guys, huh, okay? you have confidence in the laws of physics, huh? [laughter] but this is water gang, okay. how come the water didn't fall out? how many say, "well, there is probably no reason for that, it's just that when it's spinning, the laws of physics break down. okay. how come the water didn't fall out, why? i take the ball on the string

and i swing the ball around and around and around. all right, swing it around like this, okay? or like that. how come a ball goes in a circular path? maybe, because something is pulling the ball out. that's what the little kids say because you guys say, "wait a minute, there is nothing pulling the ball out." which way is that ball being pulled gang? in or out? begin with i, now try it. [laughter] okay, that's being pulled in, do you know a lot of people don't know that? they think that something is pulling the ball out. they think that when i whirl the water around and around and around, that something is pulling the water out and you have a name for that. you know what they call that? they call it centrifugal force, center-fleeing force, a force going away from the center, but guess what, gang? there is no centrifugal force pulling outward on this ball

and there was no centrifugal force pulling outward on that water. the forces that acted on both these things was pulled which way? inward. i have to pull on that string. if i stop pulling and let it go, what's going to happen? the ball is gonna go out or just continue going, and this is law of inertia. you know, the slingshot bit, take this thing like this. let's suppose the string breaks right at the bottom, right at the very bottom, right, like that. when it is at the bottom, which way does the ball go? everybody here i think know, everybody knows. how many say all of a sudden, go and hits the floor? how many say, no, it keeps going in a circle? because a body going in a circle tends to keep going in a circle, no force needed. come on, come on! how many s, you know, when that string breaks, honey, there is a ping that's gonna keep going in a straight line path. see, so long as the force acts, it will pull it in a circle. if the force doesn't act anymore, then pew, the law of inertia takes place, huh? the idea that the object moves in a straight-line path, constant speed, we don't say straight-line path, constant speed,

we got two words to say the whole thing... constant velocity, man, constant velocity. constant velocity means straight-line path constant speed. and when no force acts on this thing... tends to go at constant velocity. so there is an inward force: a force pulling toward the center. you're riding in your car and all of a sudden you're in a car and your friend takes a left turn, and phoom. you hit the door. so somebody asks, "how come your hands--" "oh, i don't know. that's centrifugal force pulled me out against door," true or false? no, what happens as you are driving along in the car, you tend to keep going straight, but the car goes like this and you didn't put your seatbelts on that day, so what do you do? you tend to keep going straight, and the car comes in and hits you. so you didn't hit the car, the car hit you. or if the car hits you, you hit the car. there is an outward force on the car, but not on you. there is an outward force,

there is a going away force on the string, but not on the ball, see that? see, the string pulls the ball in, in, in, in, in. if the string pulls the ball in: action, reaction is the ball pulls the string out, but no outward force on the ball. ain't that kind of neat? tomorrow's space colonies might look something like this. within a great big huge tire, a couple of kilometers wide, and this thing would be spinning at a constant rpms, and people out here will walk around. if you took a regular balloon tire from a car or a bicycle and you put some ants in there,

and you just took the tire and you just dropped it off a cliff, what would the ants do? the ants would just free-fall, it wouldn't push against them anymore. all the supports gone and they would just all fall. and they would say, hey wow, someone cut out the gravity, honey. but if you take that wheel and you spin it, and then you drop it, the ants will all get thrown on the outside, isn't that true? and the ants will think, there is a force pulling them out, but no, it's a force holding them in the circle. if all of a sudden there is a little hole there, the ants keep going, but the ants pulled here. so the ants are pulled, pulled, pulled. people inside a space colony, these people right here, head, feet, okay. this thing is rotating like this. and these people are thrown against the outside rim. and these people think that there is a force pulling them out like this. they think that and if you've gotten one of those amusement-type devices, those great big centrifuges, did you ever get one of those, gang? you stand up against the wall like this, okay? and then i start revving around and when it is going fast, fast, fast, they drop the floor out

and you stay there-- and you stay there, you're like, you can hardly put your head away boom, and you turn around like this, push-ups are hard to do man, okay, because you see yourself being pushed this way, but it's not happening. you're being thrown out that way, but instead of ending up down there, you're over there, because something pulls you in so. so there is an inward force pushing in on you, and you can go it is hard to put your neck out like, it goes right back, okay. centripetal force, a center seeking force, and that's what we will enjoy tomorrow when we are in space vehicles. now we can get out in regions where there is not earth's normal gravity and spin that son of a gun to a point where we can feel ourselves as if there were gravity acting on us. there is probably people in this room that will do such a thing. and i know there is one person in this room that's already designing such type things. and this is where the human race is going, outer space. we can make our own gravity, simulate gravity, just by rotating at the proper speed.

let's suppose you wanted to climb up a little tube in here and at the center, this is the hub. in the center, would you have any speed? this kind of speed? in the center, "r" would be zero and so you would be in a state of free-fall there, the little ant that was thrown to the edge inside the tire in the hub would just be floating around as that wheel fell off the cliff. and people way out beyond the moon, in one of these rotating things right in here, would not feel any gravity effect, but people out here would. the human race, just talks about that today. the human race doesn't do that because the human race hasn't got to the point where we have these things operational, yet. do you know why? because the human race is back in the 1900s.

and when the human race gets up to where there is the two instead of a one, then the human race will be doing things like this, at first a few people and then later, more. all you people have calculators. you get them in your rice krispies box, when you open your cereal. i can remember when calculators first came out, they were so rare and so expensive that at my school in san francisco, we were told, "you can't use a calculator for exams." why? because only the rich ones can have them and that's discriminating against the poor folk, so nobody can use a calculator, they are too expensive, too hard to get. and how about today? like i say in your rice krispies in the morning, there is a calculator, okay? everyone has them. and so today, how many people orbit around the world, a lot or a little?

how about tomorrow? i talked to an astronaut type couple of summers ago. and he belongs to a club where to be in that club, you have had to orbit the earth at least once. i thought to myself, must be awfully small club, it's a big club. i forget what it is, it's more than a hundred. you know what it is, tinnie? something like about 300 people that have orbited the world. yeah. there is probably someone in this room who will orbit the world. which one? stand up please. tinnie, you're going? gang, i've got a nice homework problem for you. oh, you see that dandy, you're gonna be loving it. and here it is, it's not in your book.

here it is. i got a can of chili beans. the chili beans roll down the hill. i've got a can of pineapple juice. the pineapple juice will roll down the hill. i wonder if they roll down the same. well, one is juice, one is a liquid, the other is beans, hard packed beans. which one will get to the bottom first? something with liquid in it? or something with solid in it? this is a homework problem, you hand it in two more days.

how are you gonna get the answer? you call up your friends, all right? you look in some other physics books. you talk to a physics type or how many say, "do it myself, do an experiment." do it, gang. and then see if you're cleaver enough to explain why u got the results you got. hint: do all the beans roll? does the liquid inside, roll or slide? [laughter] think about such things, write it out for homework next time, so try it. take a can of liquid, take a can of soda pop and take a can of like hard packed beans and try it at home and see if you can explain, why one seem to roll faster than the other, okay?

catch you next time, physics.

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