 Hello everyone, this is Shila Ratna Banshwade from Walchand Institute of Technology, Sola Board. Today, we are going to see the topic that is sections of solids. We will be looking into the introduction for this part. Let us move further, the learning outcomes. At the end of this session, students will be able to understand the basics of sections of solids. So what is expected in this is what are solids and what role does sections play into it? Moving further, now what is a solid object? A solid object is an object which has length, which has height and which has breadth. So on the screen, you can see a solid object. A solid object is a three-dimensional object having length, breadth and thickness. It is completely bounded by surface or surfaces which may be curved or plain. As you can see on screen, there are six surfaces for this. Here we have plain surfaces. Now to represent a solid in orthographic projection, at least two views are required. That is the front view and the other view or the top view. But sometimes the two views may be insufficient or may not be sufficient to explain the details of the solids. Hence, we go for a third view called as the side view and in that we have either the right hand side view or the left hand side view as per the requirement of the object. So to make an object very clear, minimum two or required the third view must be drawn. Then moving further, we have types of solids. Now as we have seen what a solid is. Now let us see what are the types of solids. These are classified as majorly in two groups, that is polyhedra and solids of revolution. We will look into details of each. As you can see on screen, a polyhedra is defined as the solid bounded by plain surfaces called phases. And in that we have regular polyhedra and prisms and pyramids. The first thing what you have seen in the previous slide is a polyhedra because it has plain surfaces, no curved surfaces available further. So your prisms, your pyramids, cubes, all are polyhedras. Then we have solids of revolution. In this, if we have a plain surface and it is revolved about one of its edges, the solid generated by that is called a solid of revolution. That is if you consider your scale of 15 centimeter that you use regularly for drawing, if you keep it vertical with its longest side vertical and resting on one of its small side and when you rotate or revolve this in 360s, the resulting solid is a cylinder. Similarly, if you rotate your 30, 60, 90 set square when it is placed with its short edge on the ground and vertical edge or longest edge as vertical and when you rotate it, you will get the solid of revolution as cone. So when you rotate any plane about one of its edges, you get the solid, either it will be a cylinder, a cone or a sphere. Depending upon what kind of plane you are rotating or revolving, the type or the resulted solid depends on the type of plane. So these are broad classifications of solids. That is polyhedra and solids of revolution. Let us see the images of each and every solid. As you can see on screen, these are regular polyhedrons. So the one that you have seen at the beginning of this slide was this. Then we have prisms. We have cube, we have square prism, rectangular prism, hexagonal prism and pentagonal prism. Here as you can see, the base shape determines the name of the solid. Here in this case it is square, so square prism, here it is rectangular, so rectangular prism, here it is hexagonal, so hexagonal prism, here it is pentagon, so pentagonal prism. It has two surfaces, horizontal, top face and the bottom face or top and base. Both are parallel to each other, in all cases, both are parallel to each other. We have fixed long vertical edges, long vertical edges and base sides or top surface sides. So we have defined shapes or edges for prism, whereas in the case of pyramids, pyramids are also named after the shape of the base. That is a triangular pyramid, a square pyramid, a pentagonal pyramid and a hexagonal pyramid. But here two base or two top surfaces are not available. Here we have a base and an apex at the top. So only one base is available, hence called as pyramids, hence called as prisms. And then we have the solid of revolution. The first here you can see the sectional part or the shaded part is the plane that is rotated about this axis and we get the resulting solid as cylinder. So this is the cylinder, when you rotate this triangular plane, you get a cone and this type of plane gives you a sphere. So these are solids of revolution. As you can see on screen, as far as prisms and pyramids and this regular polyhedral are concerned, there are fixed or defined edges, whereas in solids of revolution there are no edges and for solution purpose or for our understanding purpose, we consider generators. Generators are imaginary lines. They are not actually present on the revolution's solid. But we do consider for our solution ease or ease of solutions. So these are the types of solids moving for the need of section or need of sections of solids. This is your regular object in isometric form. This is the cut section of the form. Now as you can see on screen, this hole is visible, but the hole that is present at the bottom is not visible and when we draw this, we need to project it in dotted form or hidden form. Dotted line needs to be used. But when you take a sectional view or when you take a cutting plane in this way, you can directly see the cut portion here that is at the bottom. This is the corresponding orthobiographic view of this object. Here you can see this is the hidden detail that is available. So sections are to be drawn or sectional view is to be drawn when you have to see the hidden details of the object. When there are lot of many hidden details and you are not able to make it clear with the help of dotted lines, we take sections and eliminate some of the dotted lines so that the drawing becomes easy to understand and hence it can be reproduced easily without missing any details of the object. Then here you can see reducing or eliminating the hidden lines as I mentioned and revealing the cross section of the shape. Both the things are possible when we go for a sectional view. Now we have some of the parameters like what is a section plane or cutting plane. This is an imaginary plane which is assumed to cut the object as required is called as section plane. Section the surface produced when a section plane cuts a solid is termed as section. When you cut a solid that part is called as sectional part. In sectional view when you draw the views of the cut portion it is called as sectional views. So these are some of the points to be remembered when doing sections. Hatching needs to be shown in sectional views. They are exactly at 45 degrees to the boundary lines and equally spaced. Thank you.