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 l