Okay, last thing, let's see in Casimir's first year, now you're going to do the Casimir in a second year. I'm not going to use the different Casimir's second year. We'll look at the difference of Casimir's second year. So here, similar to Casimir's first year, we have a body which is on which we have applied wind forces P1P2P3XRNPN. This can be for our moments, talks, anything that we want. So, due to these loads, it'll have displacements. So, displacements are always under corresponding amounts, there is a gender, wanted, etc. So, under these loads, the bodies under equilibrium. So, it is under a stable equilibrium. So, these are loads, loads. And we can see the displacements, the first of them. So, suppose we apply a virtual displacement, that is, suppose we have displacement delta N. And suppose we increase this displacement by quantity D delta N. D delta N is the virtual displacement. So, we have displacement delta N plus D delta N. So, obviously, suppose that these forces do not have any components in the direction of that load. Or this way, forces do not have any components in the direction of the load. They are not contributed to the work. And the only load that contributes to the additional work done is people. So, the network or increase in work done is given by VN, V delta. So, we have a displacement D delta N. For this displacement, we need a small work or small load, it is given by TPN. So, we apply a small load TN, which causes a small displacement D delta N. So, we will get energy, the increase in TN, D delta N plus D TN, D delta N. So, we will increase in energy D delta, virtual displacement and the virtual load that is causes displacement. So, by similar to what we have written for Casualty N. Of course, there we can write the increased energy or increase in energy or the final energy in terms of the displacements, the first displacement is T and D delta. So, this is the final display, final energy of TN. So, what we have seen earlier, this can be similar to what we have observed that is, this is the original energy and this is the increase in energy. As we have two very small quantities, we can neglect it when compared to these quantity. So, we neglect them, we equate them and after equating, we get the numbers that is do you buy, do the time you do this. So, what this means is, if we, where you is the strain energy, so if we find the strain energy of a body and if we want to find what load causes a particular deflection, that is delta N is a deflection. So, we want to know what load is causing this deflection and we just have to find strain energy and differentiate with respect to displacement. Then we will get the load which causes that displacement. So, that sport is the crux of just the numbers second here.