Now we will do macro charge. Macro just meaning large. So in physics we often talk about a body. So I don't really mean anything specific by body, body just means a large objects made out of matter. That's pretty much all it means. In electrostatics, one of the greatest things to use as a body is Teflon. Teflon has very useful properties, which I'll be showing you very soon. So when I first taught this class, I went back into the demo closet, and said I need the Teflon rod to do all the demos, and I was extremely disappointed. This big, beautiful lecture hall with 280 seats, and full of students eager to learn about physics. This is the Teflon rod in Physics 102 at Rice University, this is what I was given to demonstrate, electrostatics. I couldn't live with that. So I got in the McMaster catalog, and I bought this. This is a Teflon rod. You can really do demos with this. You can really go to town, and explain some physics with this Teflon rod. So we will be using this Teflon rod quite a bit, in our demonstrations, and in our explanations of physics. So our body is simply a Teflon rod, and it weighs 0.37 kilograms. So what's the first thing we want to do? I guess if we want to think about charge in this rod, we simply say how much charge does it have? You can actually figure that out from what you already know from the micro scale of charge. Because you could say, this thing weighs 0.37 kilograms, and we learned that the mass of charge was very small, 1.7 times 10_minus 27 kilograms per nucleon, where a nucleon is either a proton or a neutron, so if you're talking about one or the other, we call it a nucleon, things that live in the nucleus. So we have our big mass divided by the mass of an individual nucleon, and you put those together, and you get 2.2 times 10_26 nucleons. So you actually don't need to know the chemistry of this thing or even what atoms are in it. If we know that it weighs 0.37 kilograms, we know that, that mass is almost all in the protons, and neutrons. The electrons don't weigh much, and we can actually estimate the number of nucleons in this thing. Now, another thing we didn't know about atoms is that there's usually roughly equal numbers of protons and neutrons in the nucleus. It's almost never exactly equal, but it's usually very close. With lithium it was three and four. It's usually closer than that. So if that's true, then we know that roughly half of the nucleons are protons. So we know we have 1.1 times 10_26 protons. If that's true now we can figure out the charge because each one has a charge of 1.6 times 10_19 coulombs per proton. So if we multiply those two, you end up with 18 times 10_6 coulombs. That's 18 million coulombs. There are 18 million coulombs of positive charge in this macroscopic Teflon rod. Now if I were really holding 18 millions of coulombs of charge, it would be the greatest demonstration you've ever seen in your life. It would blow you away. I mean, it would literally blow us all away out of the room, building would be gone. But we'd survive this demo. We aren't all, I guess only I, and the camera man would be blown away because this social distance thing. But we survive because there's not just 18 million coulombs of positive charge, there's also 18 million coulombs, and negative charge, this is just microscopic, and macroscopic. So in addition, all the protons, there's electrons in there so mixed together so tightly that we don't see the charge, and the macroscopic world. So it does have 18 million coulombs of protons. That it does have 18 million coulombs of electrons. But when you put them together, you get something that macroscopically just appears neutral, and this is how you have to keep in mind about macroscopic objects. When we say they're neutral, they're actually still fairly exciting. There's still a lot of charge in there. It's just completely mixed together, and balanced.