 Hello friends so carrying on with our discussion on the four fundamental forces now. We are here to discuss nuclear force So first of all we need to understand what is a nucleus. So nucleus as you know is Central part of any atom where protons and neutrons are You know are are found out right so an atom is comprised of Nucleus and Electrons so within nucleus you know there is proton there is electron. I'm sorry. There is neutrons lots of them actually so depending upon different elements Depending on their atomic numbers and atomic masses. We have different number of Neutrons and protons in one particular nucleus. So this is how a nucleus looks like so you can see there are lots of protons and Neutrons proton is a positively charged particle neutron is Neutral so there is no charge on neutron and you can see all these proton and neutrons are you know interacting with each other Interacting they are interacting right so all I have not shown all the interactions here, but this is just a Symbolic representation that the protons and neutrons are interacting so there will be interactions like these as well Interactions like these as well and all of that right so there will be lots of interaction possible Okay, so now let's study about Nuclear forces, okay, and there is another thing to be noticed over here that diameter is somewhere around 10 to the power minus 14 meter so you can imagine how small it is right So it is less than the billionth part of a meter as well So it's such a tiny distance that we will not be able to visualize it ever. It's such a small Distance now So what are the points related to nuclear forces? So first is nucleus is the central dense part of the atom, right? So rather for discovered nucleus in a late 19th century where we figured out that Every atom has a very dense part in the center and that is called nucleus now It consists of positively charged protons and neutrons which are neutral as I discussed Now the diameter of a nucleus as we saw here is 10 to the power minus 14 meters right and then in such a small space which you know There are lots of protons and neutrons confined to such a small space so there must be some force Which is acting on each one of them to hold them together now? What is that force because if you see there are lots of Repulsion between proton and proton each proton will be repelling the other proton Why we just saw in the previous session that like charges repels so hence they are going to repel each other and That too you are confining them in a small space whose diameter is 10 to the power minus 14 meter such a small space and There all these positively charged particles are held together now obviously Gravitational force cannot be Reason why because why these protons are together because if you really calculate the amount of gravitational force It comes out to be very very small, right? So because if you remember force of gravity was nothing but g into masses of two Objects divided by the distance square now if you see look at the mass of Proton mass of a proton is of the order of 10 to the power minus 27 kg So you can imagine this is you know even gravitational force will be too less if you do the calculation and G anyways, you know it was 6.67 into 10 to the power minus 11 So if you multiply minus 11 10 to the power minus 11 to 10 to the power minus 27 to another 10 to the power minus 27 it will be a very small quantity despite the fact that denominator will try to compensate that lesser Value because d itself is very small But still if I do the calculation and show you g is 6.67 into 10 to the power of minus 11 let us assume for the time being that the mass of proton is this only for the calculation sake It's not like that, but just for the calculation sake so 10 to the power minus 27 another 27 and divided by Let's say they are farthest apart and let's say the distance is around 10 to the power Minus 14, right? Let's say they are separated or they are at the corner. So 10 to the power minus 14 Let's say, okay, and there's a square on top of it Isn't it? So hence if you calculate this is very very small number, right? So in the in the numerator, you can see there is 10 to the power minus 11 in the denom in the another one Is 21 minus 27 another is minus 27 divided by 10 to the power minus 28, right? So these are roughly comparable values But then again there is 10 to the power minus 11 and 10 to the power minus 27 Sorry, this will not be 10 to the power minus 39. This will be somewhere 10 to the power minus 37 Is it at 10 to the power minus 37? So this is such a tiny force by force of gravity is very very small. So definitely force of gravity is not going to You know, keep the protons together. So hence we need something else. And what is that? That is what is called? Nuclear strong force. So these are nuclear forces holds the protons and neutrons together in such a tiny space It acts between two protons and two neutrons and a proton neutron pair Okay, it's attractive in nature. Obviously it has to why because if two protons are kept confined in such a small tiny space then it must be attractive and that too it is powerful than the electrostatic force of repulsion, right? And but the crucial thing is it's a very short-range force that is it operates in a very small small tiny distances the moment you You know separate protons Beyond some certain limit and then it ceases to act or it drops in value, right? What I mean what I mean is let's say this is the proton here and this is the proton here And let's say D is the distance where the nuclear force is acting if you Dislodge them or let's say separate them with some more distance and the force of attraction drops drastically in value And hence the nucleus will be broken understood So that's important thing to be taken care of. So this is called nuclear strong force Okay, so the name is nuclear strong force and later. We'll also see something called nuclear weak force Now this is weak force which we are going to now talk about what is weak force then guys So this is also nuclear force, but this is weaker than the previous one what we discussed now There are few nuclear reactions, which you probably would be knowing for example Neutron can get transformed into a proton and in this process It also emits an electron and another subatomic particle, which you will be studying later on and it's called anti-neutrino So don't get confused or hassled by these new terms Simply put there's a neutron neutron gets broken into a proton and an electron plus another Subatomic particle, which is now called anti-neutrino. Okay, so this process is called beta decay What is called beta decay? What all these are when you study atomic structure any chemistry and later on, you know In in physics as well, then you will understand what this process is for the time being for these type of conversions We require something called weak force Okay, so weak force are weak forces weak nuclear forces rather are responsible for such Conversion, so let's talk about them protons neutrons and electrons are subatomic particles subatomic meaning Smaller than atom hence subatomic particles weak forces are responsible for conversion of one subatomic particle to other such particles Okay, these conversions take place through nuclear reactions and a beta decay such an example Which I showed to you in a beta decay a neutron gets converted into a proton and electron and another particle called anti-neutrino and it's a short-range force again like the the strong force it acts within distances comparable to that of a size of a proton or Neutron approximately 10 to the power minus 15 meters and now these are the forces which are responsible So both strong and weak forces would be responsible in nuclear reaction. So what all nuclear reactions? You will be you would have heard of So what are nuclear reactions? So let's say we have talked about something called fission, right? Fission and we also know there is another reaction called fusion, right? So what happens in fission a big? nucleus breaks down into small Nuclear Okay, this is what is called nuclear fission in this what happens? The weak and the strong forces play a vital role again here in fusion. What happens? There are small Nuclear and they combine together to become a bigger nucleus. Okay, this is called Nuclear fusion reaction now this happens in in our Sun, right? so in our Sun, you know that hydrogen or protons basically or hydrogen ions they you know bombard each other and Helium is formed that's fusion reaction. So all these nuclear weak forces strong forces play a vital role in In these nuclear reactions, okay? Now nuclear strong force again to just to summarize is the force which binds the protons and neutrons together within a nucleus if you You know are disturb that nuclear strong force then you know catastrophe Catastrophical events happen for example the nuclear bomb which is Produced is based on this principle that if you if you try to disturb the balance of the nuclear forces And then it creates a devastating result. So hence that is such a strong force Which you know humanity has been able to exploit not only for let's say a warfare, but later on for peaceful applications like production of electricity and all so that's Nuclear strong force and similarly weak forces as I told talk to you and told you that weak forces are responsible for conversion of let's say one particle into the other these are These are these can either happen spontaneously in our nuclear reaction setup or It can be induced. So hence weak forces play a vital role there So in this in this entire few sessions, what did we discuss? We saw that there are four fundamental law four fundamental forces in nature one was law of gravity So the first thing which was discovered then law the force of electromagnetism which came after gravity And which is again a very you know Plays a very vital role in all the in defining all other forces or Generating all other forces which we'll be seeing later. Then there were two strong Nuclear forces one was strong nuclear force another was weak nuclear force This is how the you know that the four fundamental forces are There and we are going to use them in multiple multiple fields now in terms of the strength if you talk about So nuclear strong force is the strong force has the highest strength followed by electromagnetic force Okay, these are in terms of strength electromagnetic force is The second then followed by weak nuclear and then followed by gravity So you can see The gravitational force is the least You know strength in terms of strength. It is the least right? So now next we are going to discuss about other contact forces which we have Seen in the previous sessions as well and we are going to use in the next subsequent sessions as well