And this carries the negative part of the charge. Its this little electron that carries the negative charge that makes up electric currents in wireselectron. It turns out this and this, these charges are opposite and which belies a fundamental rule of electricity. Opposite charges. Attract. Attract. And like charges. Repel. Repel. Repel. Thats right. And so the negative charge is being attracted to the positive charge and whirls around, around, around in a very loose sense, in almost an incorrect sense. But we can think of it like a sun here and a planet going around and around and around. The force that holds the planet to the sun is the force that we dont understand it very well. We have a name for it begins with g. What is it . Gravity. Gravity. And the force that holds the electron to the proton is the force we call. Electricity. Begins with the e. Ends with a l. Electrical. Electrical. Its the electrical force. So theres an electrical force between these two. Now, we normally say that that atom has no net charge. Do you hear me when i say no net charge . There is much positive as negative. In fact, if i had another charge, like a charge over here, a negative, this negative charge over here wouldnt even see that. It wouldnt sense it. It wouldnt sense a thing cause this negative charge is what . Being attracted to the positive, but is being repelled by the negative, and the distances are about the same, so it turns out its a wash. So a charge over here doesnt notice electrically this atom over here. So the atom is neutral. So we have a neutral atom. But lets suppose this charge is closer, like over here, and lets suppose its part of another atom, like another hydrogen atom. Oh, this charge here now is closer to the proton than it is to the electron. So theres an attraction to the proton, a repulsion over here, which is not quite as big. Its a little further away. So we have now a net attraction. And do you know what happens to this atom here . It. [makes noise] it clumps together and it becomes a molecule. When you study chemistry, youll study about the different bonding forces. And all those bonding forces that you study, are guess what . Begin with the e. Electrical. Electrical. Theyre all electrical. You are held together by electrical forces. Electrical forces comprised all the bondings that you have in chemistry. Its simply electrical forces. And these forces behave in a way very similar to the way that Gravitational Forces behaved. Remember we talked about the force of gravity . And we said the force of gravity, there was a force in the universe that was proportional to the mass of one object, the mass of another object, divided by the distance square. Remember we talked about that . Well, physics is neat, gang, because guess what . It turns out there is a force thats very much the same between electrical charges, and that force depends upon the quantity of charge on one object, the quantity of charge on the other object and depends on the distance square. Isnt that neat . Whip, whip, same, same, which is one of the nice things about physics. Things that seem so diverse really have a commonality. And so this is called coulombs law. Coulombs named after a man about 150 years ago by the name of james j. Law. Law. Right on. Okay. And newtons law of gravity is named after a dude named. Gravity. Gravity. Okay. We got that. We got that, okay. But we have these two things here. And all the coulombs laws said is, hey, the force of attraction are repel, oh, one difference, electrical forces can attract or repel. Oh, so you can shield out electrical forces. Gravitational forces only attract. Theres no way to shield them out, but you can shield electrical forces. But it just simply says, the amount of attraction or repulsion depends upon how much charge youre talking about and how far away the charges. If theyre very, very far away, then the force will be very, very weak. If theyre close, close, close, the force will be strong. Just exactly what you would expect. The same thing youd expect with planets in the universe. Planets farvery, very massive, more force of gravity, close together, more force of gravity. Same type thing with electrical forces. Any questions at this point . Wouldnt a minus be part of the constant or proportionality for the electrical force . Class, i havent even talked about constant and proportionality, but it do you know what lee was talking about when he talks about the constant or proportionality, gang . No. Remember the constant or proportionality for force of gravity . If you took the force and divided it by this, youd always get the same number, and that was that big g, 6. 67 times 10 to the minus 11, okay. That was the constant or proportionality. Over here, if you take the force between a couple of charge particles and divide that force by the charges and the distance between, you will get the same darn ratio no matter what set up you talk about. And thats the constant of proportionality and we call it k. Over here we call the constant g. Now we dont talk about a proportion, we talk about an exact equation where g and k make this side and this side, newtons, newtons, same, same. Other questions . Yeah. From the center of an atom, you have more than one proton, which are two positive charged. Yeah. This is for a hydrogen atom, now. Yes. Lets supposed i have a helium atom. Now, we got two protons. It turns out theres two neutrons here too. And you know what . You know whats gonna happen to this space over here . Take one guess. Everyone. Everyone. This charge out here now sees two protons tugging on it. How many say, itll be pulled into a tighter orbit . How many say, no, no, no, itll stay the same . How many say, no, itll be pushed further away . Check your neighbor. How many say its gonna be tighter . Yay, thats right. And it turns out, for a helium atom, the helium will hold the electron tight. And furthermore, it will hold another one too. The fact it holds another one makes it a little bit bigger, okay, cause theyre repelling over here. But a helium atom is smaller. It turns out a helium atom wont gang up with any other atom, so theres no such thing as a helium molecule. We have two positive charges right next to each other like that, how do you deal with that . Why dont those two positive charges repel . Why dont they repel . Look how close they are. Theyre right up against one another . Why dont they repel . And let me say this, the electrical force is awesome. Its a billion, billion, billion, billion times stronger than the Gravitational Forces between these particles. Billion, billion, billion, billion. So its an enormous electrical force tending to repel them. And why dont they simply repel . Well, it turns out youre gotta get to the last chapter in the book. And the last chapter in the book you find out, honey, theres a force Even Stronger than the electrical force, yes, there is, but only upclose. And that force is called strong force or weak force . Strong. Strong force. Call it Strong Nuclear force. And its a Strong Nuclear force that holds this thing together in spite of the electrical repulsion. And later on, youre gonna learn that when a nucleus gets too big, and these charges are far away, the Nuclear Force holding them together is weak compared to the electrical force, so they fly apart. And well learn that those atoms are called radioactive atoms. And all that has to do with the electrical forces between the nucleons. So this is another force that we havent talked about that overwhelms the electrical. Any other questions at this point . Lets talk about charging. Heres a piece of cats fur. Its for science. And heres a rubber rod. What im gonna do is im gonna rub the rubber rod against the cats fur. Now, what im doing. [meowing] [laughter] [meowing] [laughter] i dont know what that is. But anyway, what im doing here, gang, is what . Im rubbing electrons from here on here. And you know why . It turns out every substance its holding its electrons, yeah . How many say, oh, all substances must hold their electrons with just the same force . Coincidence of coincidences. No way. Thats not true. Different things will hold electrons with more force than others. And guess what doesnt hold electrons very good . It begins with f, ends with r. I got a u in the middle, try it. Fur. Fur. Or your hair. Okay. Guess what holds electrons very nicely . It begins with r, ends with ubber. Rubber. Rubber, okay . And so when i take the rubber and i scrape it against the fur, what am i doing . I rub electrons from the fur onto the rod. Now, the rod has more electrons than before. You, people at front row, can you see those things . Yes. Okay. [makes noise] follow me, ill make your crops grow. Heyokay. It turns out no, im kidding around. But there are more electrons on here than before. So i say this is charged. Now, you got to tell me, negatively charged, or positively charged . Negative. Neighbor. How many say negatively charged . All right. Thats because the electrons themselves are negative. And by the way, do you know who is the one who put who gave us the idea of negative and positive charges . A first, firstrate scientist with a worldwide reputation in science. His name was bf. Benjamin franklin. Benjamin franklin. Thats right. Benjamin franklin was noted as a firstrate scientist before he became a statesman for 13 the colonies. Benjamin franklin did a lot of work in electricity. Benjamin franklin is said to be the isaac newton of electricity, an enormously prominent scientist in his day before the 13 colonytype thing and before signing the declaration of independence. Ben franklin, he did a lot in electrostatics. So this then is negatively charged and the cats fur then would be . Positive. Positive. Which, by the way, underlies a very important principle called the conservation of charge. And the conservation of charge simply says that, hey, gang, whatever charge you got, its what you got. You dont make any more, you dont make any less. All you do is transfer it from one place to another. Its like maybe a brick road. Theres so many bricks in the road. Now, you take some of the bricks off the road and put them on the sidewalk. Whats the total number of bricks i have before and after . Same. The same. Ive just put them from one place to another. And every brick in the sidewalk is matched by a hole in the road. Do you see that . So we just take it from place and put another. So if i put a certain charge on here lets say a millionth of a coulomb coulomb is a unit of charge. If i put a millionth of a coulomb on here, and thats negative, whats the positive charge . A millionth of a coulomb positive. Can you see that . Its just kinda make sense, okay . Let me get a its a pingpong ball painted with a metallic paint. Its a conductor. Now, what im gonna do, im gonna charge this rod up. Im gonna put some charge on here, onto the ball. And i think you can see that. When i get the ball charged up. Watch this now. Repulsion. Did you see that . So like charges do what . Repel. Now, lets suppose i take this glass rod and i rubbed this against a piece of silk. Now, this is gonna become what . Positive or negative . Negative. How many say, oh, i dont know. This can be positive. And we can find out if its positive by doing what . Bring it over here, and sure enoughyou see that . Opposite charges attract. Isnt that neat . Heres a nice little thing here. Lets suppose i take this down and put a nonconductor up there, like this piece of popcorn from packing material, huh . Lets try this. Okay. Now, that has no charge at all, okay . If it does, it would ground off to me. I would ground the charge. But its noncharged. Watch this. Even though its noncharged see that attraction . It attract it or attract it then repelled. Why is that true, gang . Its attraction, attraction, attraction and pretty soon i get enough charge on there so but you see theres an initial attraction. Let me try that with a charge of opposite sign. Heres a positive charge. And it still attracts. Why . Why thats true is very interesting. It has to do with the an idea called charge polarization. Let me show you what i mean. In this little piece of material here are little charges. Theyre just as many positives as negatives. When i bring the rod over lets suppose the rod is negative. The negative does what . Pushes the negative part of those molecules over to one side and pulls the Positive Side positive end this way. For example, i have a little molecule like that, it will probably go like that. Tend to pull it like this. Now, the charges are moving through the material because its an insulator. But the molecules in there, i can reorient and pull the Positive Side toward and what do we got now . Now, i got the positives and negatives. What are like unlike charges do, gang . Attract. Attract and sure enough we saw an attraction. But that would work as well if i have the glass rod, as you saw. If i have the glass rod here and i have positive charge, now, what do i do . I take these molecules and flip them the other way. This is what happens. Thats why you can take, like, a little piece of paper. Heres a little piece of paper here, okay . It has no charge. But i can charge up, say, the rubber rod and ill find out that the little piece of paper attracts. You see that . What im doing is im polarizing the charge distribution in the paper. And thats what im doing over here, too. Im polarizing it. And so now, i have my little molecules like this. The negative is pulled toward, the positive farther away. And since the positive is farther away, there is what . There is a less repulsion and more attraction because this is closer. Closeness wins. And so what happens, the whole device comes over. I can show you charge polarization in another way. I can show you that with this. Here, we have a piece of plastic. This piece of plastic holds electrons very readily. I can just beat some electrons on here, and i do that. [laughter] now thats negatively charge, huh . Now, i take this piece of conductor. Its a piece of pie pan, huh . And its metal. Metals a good conductor, easy for electrons to flow through, right . Especially if theres a little electric pressure. And guess what were gonna talk later, electric pressure. Anyone who know a name of electric pressure . Begin with a v, end with oltage. Voltage. Voltage, very good. Okay, were on to this stuff. Not so bad, yeah. But notice i have a wooden handle. Why the wooden handle . Its a good insulator. Electrons wont flow very readily through a wooden handle. If i put this down on top of there, should this be charged . I turn it over and it isnt. But what happens when i touch it with my finger . See that, see that, see the difference . Isnt that neat . Okay. So we find its charged when i touched it with my finger. Lets take a look at this in more detail. Heres my piece of plastic material and i beat a negative charge on there, yeah. And i took the pie pan and i put the pie pan on there like that, okay . Now, what happens in that pie pan . Any free charges in that pie pan . Yeah. Any charges in that pie pan . Show me the piece of material with no charges. No way. Theres charges in everything. Theres atoms in the pie pan. And arent the electrons loose in all metals . Isnt that true . So the electrons are gonna be repelled by the electrical by the negative plastic. So the electrons are gonna be pushed to the top. And whats gonna be pulled down, gang . Begin with a p. Positive. The positive, see. Im being careful to draw as many positives as negatives. Why . Because there is no net charge, and we saw that. If there are net charge now, it will flow off through my body. Okay. But now, there is none and theres still none. No net charge. But what happens when i put my finger there. What happens then, gang . When i put my finger hereokay . When i touch it with my finger, then i afford a what . Why does it become charged . And let me ask you question. When i do put my finger there, you saw it becomes charged, why . And what kind of charge . Check your neighbors. Hey, gang, i can show you that its charged by lighting up this little lamp. Let me get this away now, no charge. By touching like this, boom, no light. No light, no light. All right . Now, let me touch it. Light. Do you see that flash of light . Can you see that . Let me try it again. Let me try it in the dark. Just watch. Now we saw it. That was nice. Can you be seeing . Yeah. Yes, i can see it now. All right. Thank you. So you guys thought i was putting you on, right . All right. All right. Yey. You could light up cities like that if you had someone keep doing that, right . Yeah. We have a better way. Ill show you next week, okay . Lets look at this device here. It turns out how much charge can be stored on those little there has to do with the radius of curvature of the ball on the top, yeah. The radius of curvature. What would happen if we have a large radius of curvature . Store a lot of charge or a little . Right here, gang, were gonna be seeing this, yeah. But how about if you have a small radius of curvature like this point . Its a very, very sharp point. Very small radius of curvature. Will that store a lot of charge or a little . Answer begins with a l . Little. A little. In fact so little, it wont watch this. When i touched the point this time, and i come over like this, i guarantee you, you will not hear any lightning. Crank this thing all night long andno way. You know why no way . Because that point is so sharp that charge capacity there is so small that any charge that gets on there leaks off as fast as it gets on. So the charge leaks off and here you see there was a prevented that we prevented lightning from happening and guess what these points are useful for, gang . Lightning. On your barns and on your homes, lightning rods. Thats right. Lets look at lightning a little bit, okay . Heres the ground down below. Here comes a cloud. Maybe the cloud is all negative on the bottom. If its negative on the bottom, guess what it is at the top, gang . Positive. Positive. Thats right. And that cloud is gonna induce a charge down below here on the ground. Its gonna induce a charge. Its sort of like this cloud coming overhead and heres the ground, down below, yeah . And the cloud comes overhead and induces a charge down here. And what its gonna do is its gonna drive electrons down unto the ground and its gonna pull in effect, what up . Plus. Now, we have an interesting condition, gang. We have negative charge here. We have positive charge here. We have opposite charges like we had here with no lightning rod. What happens if the charge build up what happens finally . A baboom. Huh . And what happens when a lightning cloud comes overhead and it cant quite make it . You know why . That gap is too big. And youre out there playing golf. Youre playing golf with youre friends, huh . And youre out there and you take your copper shoes with the little cleats and you stick them into the soggy ground, right . Youre friends says, hey, we better get out of here, theres thunder clouds coming over. He say, oh, just one last time. [laughs] really one last time. You take the copper rod, okay, that copper club and you lift it up in the air and here you are right here, okay, and you lift that club right up in the air, what does the cloud say . The cloud says, santa claus has come to town. I think im gonna be making a little visit, right . Because now the path is short enough and and then you get it. Many people get wiped out every year on golf courses because they find themselves the closest part to the cloud. And the closest part, natures a little bit efficient or lazy, however you wanna put it and they get wiped out. Even that happens at homes too. If you have homes here, buildings. Do you see the buildings are closer to the clouds than the ground down below, okay . Now, this really perplexed people in the old days. Because in the old days, the tallest building in any community was you guys know what it was . Church. The church. You see . And it was always it was thought that lightning was the wrath of god. Lightning was gods way of getting angry and a little bit upset, yeah . Now, whats the last building in town that should be hit by lightning, gang . The last one especially if no one wears lipstick and wont play cards and everyone is properly guilty for any pleasure they have, okay . And what building should not be hit . But guess what building, time after time, no matter how little lipstick, no matter how much tithing, no matter how devoteful, no matter how much praying, guess what buildings were all the time getting belted by lightning . Begin with a ch. Church. Figure that one out. That had a lot of people perplexed. Benjamin franklin was a unitarian. And in philadelphia, Benjamin Franklin discovered these ideas were talking about now and he put the first lightning rod on the unitarian now, you knew you know who the unitarians are . They can play cards on saturday night. They can even drink liquor, okay . They can wear all the lipstick they want. Theyre thinking about the cosmos goes beyond those little concerns, right . But people thought that if any building gotta get hit, honey, it ought to be the and guess what . Never, the Unitarian Church didnt get belted. And one by one the churches started to put lightning rods cause whats the primary purpose of a lightning rod, gang . Some people think is to attract lightning. What did you see here is to prevent lightning. If you got a lightning rod in this church, what you do is you leak off this charge that builds up as fast as it builds on, so you wont have a positive down here and the negative. They leak up, you see . And what happened, the lightning hit over here, you say, hit the bar room over here as it should be, right . The barn, okay . Or Something Like that. But the church is spared if it has a lightning rod. So today its common place to put lightning rods on structures. The primary purpose . To prevent lightning. Secondary purpose . If get belted anyway, the lightning will be guided to the ground and spare the structure. Kinda neat, yeah . Question. Question . Where does the voltage come from for lightning bolts. I mean, its not just that theyre with the positive and negative sort are just there. How does this your question really is, how is that does build up occurred in the clouds . How does the cloud get a negative on one part and a positive on the other . Yeah. And you know what . That is still being researched. The last i heard there was still more questions than answers on that. Some people tend to think that in this day and age, we know everything. We dont know anything, really, compared to whats coming along, huh . We dont yet as my understanding, dont really how to clear understanding of why you do get that voltage difference in a cloud to begin with. Theres a lot of ideas as to rain falling down, friction rubs and sort of thing like that, but theres a lot of other questions unanswered. So i dont know really why you do get that big difference in charge that causes this whole thing to begin with. Theres several models for it as i understand. Lets look at the granddaddy here. This is called the vandergraph generator. Its named after a person by the name of robert j. Generator. All right. Wed be learning this stuff. All right. Now, what were gonna do here is talked about in the textbook. It turns out this belt is gonna carry charges from little lightning points here, deposit them up in here and will gonna build up an enormous charge on the top. Let me show you what i mean. Notice, i am, wellnotice that i am keeping this closer to the dome than my head. Guess why . [laughter] i dont want to put my head closer to than this, all right. Now, let me show you that, that does charge. Lets try this, gang. [laughter] all right. Lets try this. Do we have anyone with nice long oh, my dear, back row, come, come. [laughter] all right. What i want you to do [laughter] could you touch that . Its safe. Its all right and i gonna take your support. Stand over here, honey. Whats your name . Trisha. Trisha. Okay, trisha. Take your right hand and put it on the dome. Okay . Its all right. Ill take this away and youll start to feel its all getting charged. Shake your head a little bit. Okay. Thats good, good. Let it keep going, okay . Do it like this. Okay. You see it starting to do what, gang . It start and dostand up . Could we have you people hold hands, please . Could you hold hands . Its all right. Hold his hand [laughter] okay. Well, hold her hand, man. Hold her to her hand too. Shes nice. And hold her hand and maybe you hold back here. Yeah, okay. Hold hands. Back here. Keep going, right across the hall. Let it cross. [laughter] you get it . I feel it. Okay. Thank you, trish. Lets hear it for trish, all right . Okay. Theres one more thing i wanna show you, gang. As i wanna show you that i can light up this lamp in the dark. Robert, the lights, please. The lamp is lit. When i hold it like this, no. But like this, yeah. This, goes out. Like this, light. Ive got a question for you. Lights please, robert. When i held the lamp like this, it lit up. When i held it like this, it didnt. Surrounding this dome is a very strong electric field. Ive got a question for you, where do you suppose the electric field is stronger, close or far . Close. Close . Wont i have charges in here more energized here than here . When we talk about the energy per charge, were talking about a concept called voltage. Guess where the voltage will be higher, here or here . When i hold it like this, ill have a voltage difference. When i hold it like this, ill have the same. No voltage difference. When i hold it like this, you saw a current. When i held it like this, you saw no current. I wonder if theres a reason for that. Were gonna talk about that next time. See you then. Physics, yey. [music]. Hi, im with sfgovtv im here to discuss prop a that will be before the voters in tuesday the health care truth fund was for health care correspondents that would substantially there. The 5 member board passed the fund they mate not use the fund to pay for the costs until january 20, 0200. Preparing will allow the bodies to make payments from the fund only as the cities account balances to fully funded it has to be large enough to pay for the costs as theyre due and thus, the cities total payroll costs cant go over 10 percent. They must allow the payment and theyre limited to no more than 10 percent of the cities account or the governor and the trust board passed it. They would allow only if the agrees fund account or twothirds of the agencies Funding Board and the trust board productive. A yes vote means you want to change the charter from the Health Care Trust funneled only under specified circumstances a no vote i dontant to make thos changes. Im here with supervisor marking fel and he ppone of preparing thas. Ha me. D like to start with supervisor farrell why do you believe this prop a is important i started working on this when our city coroller said we have a 4. 4 blindfolds liability. Mber o we have retirees who woed long and a hard tossed the city of San Francisco and workers that are feasor full. Thats somhing we want to avoid a fight against we want to make su that our seniors ha their health ca that were second of all the costs for our city a hundreds of thousands o dollars. This yea as chairmaof our committee b it will gw to 500 million a year ovethe next 20 years we so prepa prop a does make sure that our cities retirees a their health care is priority for i the he in thirty years our 4 half a billion dollars liability will wipedout off the oks and well save a lot of money from 5 hured memoal days a year down and those hundreds of dollars of Million Dollars dollars will go toward ighborhood things. And to make su we put ourselves on a course everyone is spoing a im pud to be part of. Mr. Murphy would you recycle to speak to the opposition yes. Thanks supervisor so far could not its quite impressive our here to discuss that Human Resources as the supervisor pois out the city has a whole in the Retirees Health care budget about the half the size of the last budget w prop a the city sets aside money a thats t a bad thing. The idea that we can just promise things to rirees a no pay for it is obviously not a responsible concept and not something would endorse, however, prop a is on the hard choices that are associated with paipg r a 4 mrs. Llio Dollars Health care liability. You have to pull that money from somewhere and prop a puts the city on the hook r paying fo that obligation thats usually by putting fundi requiment in the charte but it didnt tell you where that money comes fm there has to taxes ithe in the meantime to come up with that moy. So the questio i would then prop is that prop a lea unanswered is that where is the money going to come from and w shout puturselves othe hook supervisor rrell. Thank you. The money isnt comi out of thin air but prop b this maudz that the City Employees contribute 2 percent of their pay. And the city for 2008 matches that with o perce so new employees from as of009 two percent of their health care is ing sad its not coming from taxpayers in San Francisco its fromity appes fm the city d county of San Francisco mr. Murphy. Sure so one of the troubling points of prop a theres a catch all the amendment that the contributions of the employee and accident planned contribution by the city are insufficient to meet the requirements othe tth you fu the city is on the hook for the balance. Which means in practical terms we have to cut fm somewhere else or raise taxes. And the picture o retee health care where we can Fund Health Care on 3 perce o peoples annual salaries is a little bit rosy. Its not something we can really bet o with health ca costs and fit costs rising at the, you know, 3 and 44 peent. Salaes rising at 3 and 4 percent rather its r greater than the pace of inflatio a greater than the contributions so we have a little bit of time level overview left are supervisor farrell when i started working on prop a it was important in San Francisco. I de sure we assaulted with ou labo a all communities. Im proud to say we have the support of ery membe othe ard of supervisors and the Democratic Party here in san ancisco and the Republican Party in safrancisco. Swms the Harvey Milk Club and every single every elected ofcial in is no this is building on prop c we passed i 2011 and i we can pass prop b well pass at the ballot and something we should be product u proud of thank you, mr. Murphy. There are promises and there are commitments. One of the pieces of lguage o the blot is about candle lights a the our promises for the roasts health care. Setting aside in law that the money will be there is a promise. Until we condominium the enemy of money to make those commitments work is still a promise. The commitment comes when i put the effort on t table to mke health care sewer secu. Thpromise is nice but we have to figure out how to delir and the s that are available so far fm the measu that the supeisor vitals i cites are again, a nice proble but thats not alty when we passed proa we shod know where the resources come om we hope this information has been iormation active. Please visit the San Francisco sf electio remember the voting t is available in city hall be sure to vote you have the right to remain silent. You have the right to be heard. Anything you say can be used against you. What you say will be listened to with dignity and respect. You have the right to information and assistance. [ cell door closes ] justice isnt served until crime victims are. Major funding for earth revealed was provided by the Annenberg Cpb project. This ancient meandering river provided sustenance for one of the earliest civilizations on earth