 I am Mr. D. J. Doshi working as assistant professor, Department of Mechanical Engineering, Valchin Institute of Technology, S.O.L.A.P. Today we will be discussing all about introductions of solids. What are solids? How those are drawn? What are different features of it? At the end of this session students will be able to discuss the different types of solids. Solids are 3D objects having length, breadth and height. It has length, breadth and height bounded by surfaces which may be either plane or curved or combination of both. Minimum two views that is front view and top view are necessary to represent the solid in orthographic projections. Solids are classified under two main headings. One is polyhedron and another is solids of revolution. So first we will discuss about polyhedrons, polyhedrons. So now this is called triangular prism. So prior to that what we will study, see in case of prisms. If you observe, polyhedrons are again prisms and pyramids. So in case of prisms, these are called as side faces. So now this is a triangular prism, so there will be one, two and this one, three. Three side faces will be there. The view of which will be a rectangle. Now these are, all faces are a rectangle because whereas as it is a triangular prism, it is base and a top surface. So this is the top face and this is the bottom face. These are triangular one. If it is a rectangular one, that will be rectangular one. And the center line drawn from the base center to the top face center will be a section, will be a axis line. Now these are two surfaces, meeting each other, matching with each other at this state. So this is called edge of surface. So these are the two faces which are meeting each other. This is called as a base, sorry, edges. These are called base edges. So there will be, in case of triangular prism, there will be three bases and three top bases. And this is called axis line. These are called generators. Now second one. So this is a square prism, again this is a base, this is a top base, this is axis line. As shown, you have to draw or you have to represent axis line like this. And these are all rectangular faces which are longer faces or larger faces and these are smaller faces or smaller edges. So these are faces, these are called edges. Now its base will be a square and top base will also be a square, whereas faces will be rectangular and this is the axis line. So it is called square prism. This is called pentagonal prism. So if you observe bottom base or base edge and top base will be a pentagon, symmetric to each other and we will be joining the base corners. So these are called base corners where these two base edges are meeting with each other. So these are all base corners and these are all top base corners. So we will be joining this line by vertical lines. These are generators and these are all rectangular faces or side faces. These are shaped as rectangular whereas this is a pentagon in case of pentagonal prism. This is a hexagonal prism. So again top base and bottom base will be a hexagon, regular hexagon if it is a regular one and similar one. So we will be joining the corners of the base, top and bottom with the straight line. So these are all generators and these are all rectangular faces or side faces are all rectangular whereas top and bottom will be a hexagon. So this is called a hexagonal prism. In this case center line or axis line length will be given and side of the hexagon will be given so that you can draw the related prism. Now this is a rectangular prism. So this will be a rectangle of given size. So this side will be given, this side will be given. These are symmetric to each other. So this is a top base end and this is a bottom base or bottom end. These are all base edges. This is a corner, base corner and this base corner and this top base corner we will be joining to complete the prism. In case of rectangular prism there will be vertical four lines and these are all rectangles and these are rectangular faces. So these are different types of prism. Now another part or another type of the polyhedron is pyramid. So in case of pyramid, now this is a triangular pyramid. If you observe these are three base edges drawn as per given triangular sizes of the triangular sides of the triangular triangle and this will be apex. So apex will be situated at the center of the triangle vertically projected upwards and this is the axis which is perpendicular to the bottom base from the apex which will be lying on the center line and this is called axis of the pyramid and length of this will be given to construct the pyramid or construct the front way and top way of the pyramid. So these if you observe in case of pyramids all the side faces will be triangular one whether it is a triangular pyramid or rectangular pyramid or pentagonal pyramid or hexagonal pyramid or so on. So axis is vertical which is perpendicular to the plane and these are all slant edges. In case of pyramid, these all these edges will be slant one. In case of prism those were vertical one or perpendicular to the plane but here these are all slant lines joining from O to the corner of base. So these are three corners in case of triangular pyramid. So we will be joining O1, O2 and O3 and 1, 2, 3 will be the base and these are all triangular faces. Now this is a rectangular pyramid. So the base will be a rectangle, base will be the rectangle, there will be four corners to the base. The apex will be on the line, axis line drawn perpendicular from the center of the square or center of the rectangle. In case of rectangular pyramid it will be rectangle, in case of square pyramid it will be a square. Draw a perpendicular line on which on the given length of the axis you will get the apex O this is called apex and join this with each corner of the base. So you will get a pyramid. So this is a rectangular pyramid, now this is square pyramid. So in this case as I told this base will be a square, here it will be a rectangle, here it will be a square. And axis length will be given which will be on the perpendicular line drawn from the center of the square and equal to the length of the axis. So you will get O dash here or O here which will be joining with O1, O2, O3 and O4 and the axis will be drawn shown or represented like this. So this will be a square pyramid. So in case of pyramid all the faces, side faces will be triangular one. Now this is pentagonal pyramid. So you have to draw a regular pentagon as per given size from which draw from the center of the pentagonal shape you have to draw a vertical line or perpendicular line equal to the axis length and join that apex, this is called apex with each corner of the base to get the generators of the pyramid and all the faces, side faces will be triangular. So these are all faces, triangular faces. Now this is hexagonal pyramid with a base of which will be hexagon. Again draw a perpendicular line through the center of the hexagon equal to the axis length which will be apex, join all the corners with a slant line and you will get the generators for the hexagonal pyramid and all these faces will be triangular faces. This was about polyhedrons or now one more polyhedron which is known as tetrahedron. So in case of tetrahedron it is nothing but a triangular pyramid but all these faces one, two and three faces and the base will all be equilateral triangles, will all be equilateral triangles. So from this triangle you will draw a perpendicular line, the center of the triangle you will draw will be equal to, these all lengths will be same. So accordingly you have to consider the equilateral triangles in the shown view that is called tetrahedron. So this is all related to polyhedrons. Now in solids of revolution there are two types cone and cylinder. So cone in case of cone base will be a circle from the center of the circle draw a perpendicular line name it as equal to length axis length from here draw a tangent to it and tangent to it circle given circle that is known as cone. So this will be this top view will be a circle, up front view will be a circle depending upon where it is situated. Similarly cylinder in case of apex there will be two parallel circles to each other in different plane and draw tangents to it. So this is called a cylinder. So these are the reference books used for that. Thank you.