Hello everyone and welcome to another episode of Ask of the Assist. On a very explosive topic if you will. Robanda120055 asks, could you talk about nuclear and atomic bombs? And she answers yes, in fact I am very happy to. Not only because there is very interesting physics in this topic but also because, well, nuclear weapons have played quite a significant role in the history of the world. For example in the unfortunate events in Hiroshima and Nagasaki during the Second World War. And also play a major role in politics today which is unsurprising seeing that one ton worth of nuclear weapons produces an equivalent amount of energy as 6 million tons of TNT. So yes, I am very happy to talk about this topic. Well, before we get to the exciting part, let's start by clarifying what we mean by nuclear, when we talk about nuclear weapons. As I've mentioned before, every piece of matter you've ever seen consists of atoms, billions of them. And every atom consists of electrons on the outside and the nucleus on the inside. The core of the atom you will. Now this nucleus consists of what we call nucleons and these can be other protons or neutrons. Now a nuclear reaction is a reaction in which the number of nucleons in the atom changes. And these are in fact exact sort of reactions which allow nuclear weapons to work. It is very much lacking chemistry where we take a number of things, put them together at a given temperature and get new things out plus a bit of energy. The difference is that in physics we actually know where that energy comes from. And as ever so often in physics it brings us back to Einstein. And it's famous formula E equals MC squared. Now what this formula means is that mass, the thing you weigh on a scale and energy that is heat, kinetic energy or radiation, are interchangeable. That means if you convert it, a given amount of mass into energy, you could find out how much mass it is if you times it by C which is the speed of light squared. That means even a small amount of mass can produce a very large amount of energy. Now the funny thing about nuclei is that if you take a given nucleus, you weigh it and then rip it apart into its different nucleons and then weigh those again as separate entities. You will find that the nucleons, weighted separately, have a greater mass than the nucleus itself. So we see that when a given nucleus apart we somehow gain mass and vice versa. If we could give a nucleons into a given nucleus we somehow lose mass. Now this mass isn't just lost but as we know from Einstein's formula is in fact converted into energy. This is actually the energy we get out in nuclear reactions. Now all of you are probably wondering how is this possible? How can it be that arranging nucleons and the nucleus changes their mass? Well to explain why I have to introduce you to a new force in nature which is the strong or also called the nuclear force. Now if you remember from a previous video of mine I have talked about the electromagnetic force which attracts oppositely charged particles such as protons and electrons together and repels particles with the same charge. Now the strong force is quite different from that as in it doesn't care about the charge of the particle and instead only acts on nucleons and attracts them together no matter what. Now the reason we call it the strong force is that on a nuclear level it is much much stronger than the electromagnetic force. In fact if you bring two new clons close enough together they will attract each other through the strong force and the electromagnetic force becomes almost netiable. Now the question is what happens when you pull two particles which strongly attract each other apart? Now the principle is similar to what happens when you try pulling apart a rubber band. As you pulling it apart you start storing up in it potential energy as we call it. We know this because when you let it go it will shoot together again and you might even hurt your fingers. That is the rubber band converting potential energy into kinetic energy but that's not the point. The point here is that the particles which are being pulled apart store up potential energy and as we know from Einstein's equals mc squared energy and mass are interchangeable. So an actual fact pulling particles apart increases the overall mass of the system. Vice versa pulling particles that attract each other together decreases the overall mass of the system because you're reducing the amount of potential energy. And this is actually the energy we get out in nuclear reactions. Now this explains why combining different nucleons into one nucleus causes energy to be released. More importantly it shows that merging smaller nuclei into bigger nuclei also can release energy. For example in stars like our sun hydrogen nuclei are merged into helium nuclei and eventually helium nuclei are merged into carbon and oxygen nuclei. These processes all release energy which fuels these stars. Now processes where nuclear are merged are called nuclear fusion. However what you have to take into consideration here is that the amount of energy you get out of the given nuclear fusion process depends on how tightly the nucleons are about in the initial and the final state. When you're using hydrogen to helium or when you're using up from helium to carbon you make a very significant change as at first an helium for instance most of the nucleons are essentially part of the surface of the nucleus. While in the carbon nucleus many of some will be completely bound on all sides. I.e. the binding that each nucleon experience is as much greater in the carbon atom. In other words there's a great change in potential energy in this fusion process and thus a lot of energy will be released. However when you fuse carbon into a bigger nuclei the change in binding of each nucleon in the nucleus will be much less and as a result the energy per nucleon we can gain from fusion nuclei together decreases as we get to bigger and bigger nuclei. Also another effect that we need to take into account is that as the nuclei get bigger and bigger they contain more and more protons. And as you know protons were pellic each other which actually counteracts the attraction from due to the strong force between the nucleons. And once this effect becomes significant enough the energy that can be released from fusing nuclear together actually becomes zero. For even bigger nuclei the energy actually becomes negative. In other words at this point we can actually release energy by splitting the nuclei apart. This process is called nuclear fusion and it's the principle upon which the first nuclear weapons were based and I'm getting to those right now.