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Anderson Video - Fundamental Forces and Charge

Professor Anderson
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 Hi guys. Welcome back to another edition of the learning glass lectures on physics. We're continuing our discussion here, we're going to talk about more of the fundamentals of physics and we are talking about electricity and magnetism this term. So this is very important stuff, it helps us understand the universe around us. It governs a lot of the behavior of you and me and what happens in chemistry and what happens in biology and it's a it's a really fascinating topic. Let's just back up for a second and let's talk a little bit about the four particles that we had mentioned earlier and the four forces that we need to be worried about. So there are four particles at normal everyday energies. When you get to high energy physics you can add some more particles into the mix but there's four that we need to worry about here in our local environment. One of course is the electron. The second is the up quark. The third is the down quark, and the fourth is the neutrino. Okay, these are the four basic particles that you need to worry about. Now electrons you're familiar with, everybody's heard of electrons, the rest maybe you're not so familiar with but you kind of are because it turns out the up quark and the down quark go into the proton but they also go into the neutron. A proton is two up quarks and one down quark. A neutron is two down quarks and one up quark. Okay so protons and neutrons are in fact made up of quarks. And then the last guy on the list is the neutrino, the little Neutron, and the neutrino is zero charge, nearly zero mass, zips around the universe at the speed of light, goes through almost everything without leaving a trace, very hard to detect, it was predicted theoretically and then verified experimentally. Okay, so those are the 4 particles that you need to worry about and there are four forces that we also need to worry about. The first you're very familiar with: gravity. All right, gravity is what keeps you in your seats, keeps us planted to the earth, but also keeps the earth in its rotation about the Sun, gravity. The second is what we're going to talk about this term: the electro magnetic force, and the electromagnetic force combines electricity, which you've heard about, and magnetism, which you've also heard about, but it's sort of a new idea to combine them. It's only 140 years old since Maxwell wrote down the equations for electromagnetism that we really combine those two separate things: electricity and magnetism. All right, the third is the strong nuclear force. This is the thing that holds the nucleus together, okay. It has to be strong because in the nucleus you have all these protons and all those protons want to blow apart, okay, they want to separate from each other and there's some force that holds them together and that is the strong nuclear force. In fact, if you took a whole bunch of protons and put them in a nucleus and now you hit that nucleus, you can in fact split it in two and those two chunks of protons will separate very violently. So violently that they can knock into other atoms and split them in half as well. And this is of course what happens in the atomic bomb or in atomic energy, right? You get this nuclear fission, the nucleus fizzes into two. Okay, the strong nuclear force tries to hold it together but if you get them further--far enough apart they separate, the electromagnetic force kicks in and they push apart very violently. And then the last thing is the weak nuclear force and this has to do with radioactive decay. So last term we talked a lot about gravity, this term we are going to talk about electromagnetic forces and how charges behave in the presence of electromagnetic fields. All right, let's talk about this idea of charge. Charge is fundamental to understanding electromagnetism and you already know a little bit about charge probably because you've taken chemistry classes and one electron has a charge on it. One proton has a charge on it. A neutron turns out to have no charge on it and that's where it's got its name, Neutron-neutral. Okay so one electron has a charge of negative one point six times ten to the minus nineteen coulombs, that's what this capital C is, it's a coulomb. A proton has exactly equal and opposite, one point six times ten to minus 19 coulombs positive. One Neutron has a charge of zero. And this thing in right there, the capital C, that is called a Coulomb, and that's a measure of chart so one electron is a pretty small amount of coulombs but we have a lot of electrons floating around right? We've got a lot of electrons, we have a lot of protons floating around. So the rules for charges are the following and it's really easy to remember. Likes repel, opposites attract. That's it, likes repel opposites attract. If I take two negative charges and I put them next to each other in space, they repel. There is a force that is trying to push them apart. If I take a positive charge and a negative charge, there is attraction between them, there is a force trying to pull them together. Now by Newton's third, you know that you have to have equal and opposite forces. So if I have F to the right on this one, I have to have F to the left on that one. And likewise down here if I have F to the left on the negative charge, I have to have F to the right on the positive charge. Okay, equal and opposite forces. Now this configuration right here might look a little familiar to you guys. Does anybody here know what that is? Sam do you know what that is? Where might you find a positive charge and a negative charge right next to each other? I'll give you a hint, what are we made of? Yeah, like in the universe, where might you find a positive charge and a negative charge right next to each other? What's that? In atoms. Exactly, this is an atom right here. Okay, let's talk about atoms.