Learn about Cylinders and Prisms In this lesson, let’s learn about Prisms and Cylinders. And the problem given to us wants us to name each of the 3D figures given to us, and we have to also tell whether it’s Polyhedron. So what do we know about Polyhedrons? Polyhedron is a 3D figure with flat surfaces so, all surfaces are flat and each of the flat surfaces is a Polygon. That’s the only requirement. So let’s look at the first one. We can see all the surfaces are flat and each one of them is a rectangular parallelogram so, yes, it is a polyhedron. As you can see, each of the surfaces are flat and each of them is a rectangle. So now, I can name this three dimensional figure. There are some interesting characteristics that we see. We see that we got two rectangular bases. We got two bases that are parallel to each other which mean they’re equal distance; the distance between both bases in any given place is the same. We also see that they are supported by four, this is one, this is the other, this is the third, this is the fourth, four rectangles between these two. So, whenever we have two bases that parallel to each other, it is a Prism. Now, we also in order to name the prism, we have to see the shape of one of the bases. The shape of the bases are rectangle so, this is a rectangular prism. Key thing to remember about prisms is they have two bases that are parallel to each other and the shape of the prism determines what we call it. Now, let’s look at the second problem. The second one shows us that it’s got two flat surfaces but this is a curve surface. So, this is definitely not a Polyhedron and the reason its not, is because not all surfaces are flat. There’s a curve surface here. What would we see? We got two circles as bases. Two circles as bases and they are equidistant, they are parallel to each other separated by curve surface. Such an object is called a Cylinder. So quickly recap a Prism has two bases that are parallel to each other. If they’re supported by other rectangles and their bases are rectangle, it’s called the Rectangular Prism. And if you have two circles as bases which is not a Polyhedron but it’s called a Cylinder if they’re parallel to each other.