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## Class 6 (Old)

### Course: Class 6 (Old) > Unit 9

Lesson 6: Three dimensional shapes# Recognizing common 3D shapes

Learn about 3D shapes! A square pyramid has a square base. A rectangular prism is a box shape with all rectangular sides. A triangular prism has triangle faces on opposite sides. A sphere is like a globe. A cylinder looks like a can with circular faces on top and bottom. Shapes are fun!

## Want to join the conversation?

- what is a vertice?(22 votes)
- A vertex (vertices is the plural of vertex) is a point where the sides of a shape intersect. So basically any corner on a shape is a vertex.(14 votes)

- how do i find surface area(14 votes)
- You find the area of each side of the object and then add them all together.(12 votes)

- Would a shape with an octagon for a base and triangles for sides meeting at a point be called an octagonal pyramid?(5 votes)
- Yes,an octagonal pyramid is a pyramid with a base that's a polygon with eight sides, or an octagon, and triangular faces, or sides, that meet at a point directly above the bottom.(6 votes)

- What kind of polygon have 100 sides ?(3 votes)
- Think of a century as 100 years, so it would be a centagon. This is like a decagon is like a decade (10 years).(6 votes)

- A sphere is a circle right?(2 votes)
- It may seem that way, but technically, a sphere is a 3-D shape (has width, height, and depth) and a circle is 2-D (width and height) A circle is missing the depth needed to become a 3-D shape. Also, you find volume for spheres and area for circles. This then changes the formulas.

Circle: A = pi*r^2

Sphere: V = 4/3*pi*r^3

Good luck in your journey through geometry!(7 votes)

- The Rectangular prism is also called a Cuboid. True or False?(3 votes)
- That is true. A rectangular prism is also called a cuboid. A cuboid is a three-dimensional shape that has six faces, all of which are rectangles. A cuboid is also a right prism, which means that its bases are parallel and congruent, and its lateral faces are perpendicular to the bases. A cube is a special case of a cuboid, where all the faces are squares. However, not all rectangular prisms are cuboids. A rectangular prism can also be oblique, which means that its bases are not aligned one directly above the other, and its lateral faces are parallelograms2(4 votes)

- At1:50, Sal says "This has sides that are triangles", doesn't he mean faces?(2 votes)
- I think he means bases.(2 votes)

- It is fun doing stuff like this :)(3 votes)
- I don't know what a vertice is(2 votes)
- what the differences between vertices and edges?(2 votes)
- A vertex is where two or more edges meet, so a vertex is a point and a edge is a line segment.(2 votes)

## Video transcript

- [Teacher] I have five
three-dimensional shapes over here. I also have five names for them. What I want you to do is pause this video and think about which of these
shapes is a square pyramid. Which of these is a rectangular prism? Which one is a triangular prism? Which one is a sphere and
which one is a cylinder? Let's just work through this together. Really, this is just something to know, because some people in various subjects will sometimes throw out these words. First, let's think about which
one is the square pyramid. This shape here on the right
clearly looks like a pyramid, and the thing that makes
it a square pyramid is the idea that its base is a square. Let me see if I can shade this in. So the base of this right over here is a square. That's where the square
pyramid comes from. If it's a triangular pyramid, then the base would only have three sides, but this is a square pyramid. So let me... Move this over there. So that is a square pyramid. Alright, let's do the next one. Which one is a rectangular prism? A prism you can view as a
three-dimensional object, and since it's saying a rectangular prism, well, the best one here
that is rectangular, notice, this shape right
here is rectangular on every side, and it's three dimensions. It is a prism, and so this
is the rectangular prism. So let's move that over. So that is our rectangular prism. Now, triangular prism. So this one is interesting. If you look at this shape right over here, it has sides that are triangles. You see this up here is a triangle and you see this down here is a triangle, although they're connected
by these rectangular sides. This is actually what's
called a triangular prism. In a square pyramid, the
faces which are triangles all meet at a point. In a triangular prism, you
have two opposite-facing sides that are triangles. You'll see all of these
in different orientations. Sometimes it'll be resting like this, sometimes it'll be on it's side, but this is a triangular prism. Let me... So that is a triangular prism. And so we have two left. You might be able to figure these out. Which one is a sphere? When I think sphere, I think of a globe. This choice right over
here is clearly a sphere. Let me move that over. Let me move it over, okay,
so that one is a sphere. Then last but not least, this
thing that looks like a can is a cylinder. So let me move that over. So that is a cylinder. And we're all done. So these are just useful
names to know for shapes. Cylinder is... You have these two faces that are circular and then they are opposite each other. It's kind of like a triangular prism, but instead of having these hard edges because you have a
triangle, you have a base that is a circle and a
top that is a circle.