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Current time:0:00Total duration:11:46

Triboelectric effect and charge

Video transcript

I'm guessing that you've had the experience of rubbing a balloon against your hair and then when you take the balloon away from your hair your hair sticks up and if you haven't had that experience you might think about trying to lead a more rich and fun life but I'm guessing most of you all have have done that and you've had a sense that it had something to do with the balloon or your hair somehow exchanging charge or now one's going to be more positive or negative than the other and so now they are somehow attracted and if you are thinking of those things you are generally right what you just experienced after you rub the balloon on your head and then your hair is is now attracted to the balloon that's actually called the tribal electric effect let me write that down tribe Oh tribe Oh Electric electric effect and human beings have been observing this for a long long time it didn't necessarily wasn't necessarily with with balloons at birthday parties or whatever it's with other things they rub a silk cloth on a piece of glass and then they'll see that there's some type of attraction or they might see that if what they do that enough one of the objects might discharge when it touches another object people have observed things like lightning where it looks like there's some type of a build-up and some type of potential then all of a sudden discharge 'iz and you have this lightning and then this this is thunder you know blast a sound that happens to it so this is this is something that humans have observed for a long long time and and scientists or people with a I guess you could say a scientific mind have been trying to understand it for a long long time and trying to come for framework for what exactly is happening well lucky for us we now have a framework for it that explains it quite well and that framework for what is going on with this tribal electric effect is the framework around charge is a framework that we now have around charge and this tells us this this way of looking at the world says look there are some things that just have a property called charge some things have a positive charge some things have a positive charge and it's somewhat an arbitrary name we just happen to call it positive and some things have what we say is an opposite charge or a negative charge a negative charge we could have called this the magenta charge and this the green charge we could have called this the hippopotamus charge and this the ostrich charge and we could have said that hippopotami I believe plural form eponymous they're always attracted to ostriches and they always repel other hippopotami and likewise the like charges repel or or like hippo well you get the general idea but I'll stick to the words that people are used to using and so if we if we say something has a charge say positive charge and something else has a negative charge then in our framework that we've we were setting up these two things are going to attract so opposite charges are going to attract while like charges are going to repel so if you have a positive charge and you have a positive charge these things are going to accelerate are going to accelerate away from each other and that's not just true for positive positive that's also true for negative and negative these two things are going to repel because they are they are like charges now it's very interesting to think about this because we're so used to thinking in terms of charge even you know if you is especially in kind of the world of electricity you have the positive and negative terminal you think about charging up your phone or whatever else that it just seems like ok we completely you know charges just is something that is fundamental about the universe and that's true to some tool that's that's true but you you would have to appreciate that these are these are arbitrary words and they're really just to describe a property that we have observed in the world and if you go down to the atomic level we can get to a fundamental level of where the charge is happening but once again these are really models for our brain to describe these are frameworks and models for our brain to be able to predict and describe what we observe in the world but if we run with this model we can imagine at the atomic scale the nuclei of atoms are composed of protons and neutrons so if you have some protons and then you have some neutrons I'll do two of each you have some neutrons and based on this framework proton have a positive charge protons have a positive charge now once again this convention of calling them positive and putting a plus on it it's not like protons have a little plus sign of tattooed on to them somehow we could have called those we could have said they have a a red charge or we could have even said we don't even have we wouldn't have have to even use the word charge this is just the convention that we have decided to use and so we say protons have positive charge and then Oh kind of buzzing around the nucleus of an atom you often or usually or like I say they often have electrons and electrons have a lot less mass and mass is another interesting thing we associate mass it's just so this is just something that we get we understand it in our everyday life but even mass this is just a property of objects it's just a property of matter and we feel like we understand it because on our scales we understand notions of things like weight and volume but even mass can get quite exotic but anyway the whole point of this video is not to talk about mass it's just talking about charge but all of these things that we talked about in physics these are just properties that that are that help us deal with these these notions these behaviors in different frameworks but anyway let's get back to this little atom that I was constructing so list this atom let's say it has two electrons and obviously this is not drawn to scale and each of these electrons have a negative charge and they're kind of jumping around here buzzing around this nucleus of this atom and the reason why this this this model you know even going down to the atomic scale and thinking in protons and electrons is interesting is it it allows us to start explaining what is happening in the triboelectric effect what is happening in the triboelectric effect is when you rub that balloon on your hair because of the property of the balloon the material of the balloon and the materials of your hair when they come in contact and they rub the balloon is grabbing electrons from your hair so your balute the balloon is grabbing electrons from your hair and so it is getting more negatively charged it is getting more negatively charged and then your hair is getting more positively charged or essentially just lost its lost these electrons and so when you put your when you put the balloon when you put the balloon now close to your hair remember like charges repel each other so the the electrons in your hair try to move away from these other electrons a negative charge tries to move away from the negative charge and I guess you could say that the the tips of your hair will then become more positive are more positive and they will be attracted and they will be attracted to the balloon so we can think about what's happening in terms of transfer of electrons and that's exactly what's happening and so when you think that way is like okay well you know we are scientists we you know this is a nice model we can start to think about what's happening here this model actually explains a whole ton of behavior that we've observed in the universe including things like like like lightning and and whatever else and you know the static shock that you get when you might touch a doorknob after rubbing your shoes along the carpet but we like to start we like to quantify things so we can start seeing how much they repel or how much they attract each other and so the fundamental unit of charge or one of the fundamental units of charge or I guess you could say the elementary unit of charge is that is defined in terms of the charge of a proton or an electron so the fundamental or I guess you could say the elementary unit of charge is denoted by the letter E and this is the charge of a proton and this is e for elementary charge of proton and the charge of an electron even though an electron has a much much much much smaller mass than a proton most of the mass of an atom is from the protons in the neutron so an electron has a much much smaller mass than the protons and the neutrons but it has the same but opposite charge as a proton so sometimes the convention is to write negative E or maybe even negative 1 e sometimes it depending on how whether you view this as a kind of the actual charge or whether you view this as a unit but here we'll view this the actual charge you could view negative E as the charge as the charge of an electron and something that has no charge like a neutron we say they're neutral and actually that's why they are called that is why they are called neutrons because they have their neutral they don't have charge so that right over there that over there is is a neutron now when we start to get on kind of a larger scale not on a subatomic scale anymore talking about electrons and protons the the unit of charge right in general the unit of charge that we typically use is the Coulomb is the Coulomb Coulomb it's named it's named for Charles Augustin de Coulomb so if we're talking about the the guy we would and he was an 18th century French physicist we would use capital C but if we're talking about the unit's we would use lowercase e the Coulomb the Coulomb and the Coulomb is defined so one Coulomb let me write it right over here one Coulomb and it's used abbreviation uppercase e is equal or I'll say approximately equal to we're going to round here it's approximately equal to six point two four six point two four times 10 to the 18th e or you could say in magnitude wise its equal to the charge of six point two four times ten to the eighteenth protons or magnitude wise would be the opposite if you're talking about electrons it'd be six point two four times ten to the eighteenth electrons now if you want to go the other way around what is the charge of the magnitude of the charge of say a proton in terms of coulombs well you would just take the inverse of this so you could just you could say that E is approximately equal to the inverse of this which is one point six oh I guess you could say the reciprocal of this one point six zero times ten to the negative 19 Nega times 10 to the negative 19 coulombs so hopefully this gives you an appreciation for I guess at a base level what charge is and in some ways it's like you know it's this everyday thing you're used to it we're used to dealing with electricity and we'll talk much more about that and in depth but on some levels it is this you know with it's this thing one of the mysteries of the universe how did these two particles know to attract each other you know it looks like they're at a distance how do they immediately exert a force on each other how do these particles know immediately to repel each other it's not like they have a wire connecting them that they're communicating somehow or well I guess once you get quantum mechanical an argument can be made that they are communicating somehow but in our everyday kind of logical sense it's like well at a distance how do these things actually know to repel or attract and what is this charge anyway you know we've put all these names around it but to kind of help us think about it and have a framework and predict what will happen but do we really know what this charge thing is so on one level it's kind of playing on mundane and it deals with balloons and hair but on another level to this deep thing about this universe it's a it's a it's a deep property of matter that we can on we can manipulate and we can predict but it is still this very fundamental and somewhat mysterious thing