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Cousin Fal's shape collection

Sal classifies shapes based on their number of sides, number of corners, and side-lengths. Created by Sal Khan.

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Video transcript

- [Voiceover] Oh look, it's my cousin Fal! Cousin Fal, what can I do for you? - [Voiceover] Hey Sal, what's up? - [Voiceover] Oh, well not much, I'm just sitting here thinking about what video I should do next. - [Voiceover] Well then maybe you can help me. I'm starting a shape collection. - [Voiceover] Okay, so how do you need help? - [Voiceover] Well look at these shapes over here! I have no way to classify them! - [Voiceover] Okay, well there's a bunch of ways that you could classify them. The first way, you could think about how many sides each of these shapes have, so that's one way to think about it, how many sides they have. - [Voiceover] How do I figure that out? - [Voiceover] Okay, well let's look at each of these and think about how many sides they have. So this first shape right over here this is one side. We see this kind of straight right over here, it's the straight line between these two corners, so that's one side. Two sides, three sides, and four sides. So this shape right over here has four sides. - [Voiceover] Okay, I think I get it. What about this shape right over here? - [Voiceover] Okay,well let's see. This one, well same idea, this one also looks like it has one, two, three, and four. Four sides. - [Voiceover] What about this one? - [Voiceover] Okay, well this one, actually this is interesting. This one actually had no corners, and it has no sides, there's no straight edges over here, this thing is all curved. So since it has no corners, it also has no sides, or at least the way that I'm thinking about it. So I would say that this one over here has zero sides. Let me write that a little bit neater for you. - [Voiceover] Okay yeah, I like to write things really neat. - [Voiceover] Okay, zero sides. And it has zero corners. Actually let me write them for all of them. This one has four sides, and we could also count the corners. We have one, that's where the two sides meet. One, two, three, four corners. This shape over here, it also has four sides, we already counted that and it has one, two, three, four corners. So four sides and four corners actually describes both of these shapes, this one has zero sides and zero corners-- - [Voiceover] What about the green one? - [Voiceover] Okay, well let's just see. One side, two sides, three sides, and four sides, and it also has one, two, three, four corners. So this is also four sides and four corners is also true of that one there. - [Voiceover] Do all shapes have four sides and four corners? - [Voiceover] No no, not at all. I mean this one right over here had zero sides and zero corners, and actually this last shape right over here, doesn't seem to have four sides or four corners. If we count them, we have one side, two sides, and three sides. So this one has three sides, and if we count the corners we have one corner, two corners, and three, and three corners. - [Voiceover] Oh, thanks a bunch Uncle-- Cousin Sal. But I always get confused whether you're my cousin or my uncle. But I'll call you Cousin Sal. But I read in a shape magazine that there was other ways that I can classify. I can classify based on whether the sides have the same size. So which of these have all the sides are the same size? - [Voiceover] Okay, well calm down. Let's look at this. So if you look at this one, it has four sides. But we see, that this side right over here, this green side, is clearly shorter than this purple side. So all the four sides here are not the same length. But if we look at this shape right over here, this side at least looks like the same length as this side. And that looks like the same length as this side, and that looks like the same length as that side. So it looks over here like all four sides are the same length. And that's also true for this shape. This side looks the same length as that side, looks the same length as that side, looks the same length as that side. That's also true for this three-sided shape. This side looks the same length as that side, This is the same length as that one. - [Voiceover] Oh, thank you so much Cousin Sal! I'm ready to go classify my shape collection. This is awesome! - [Voiceover] Well I'm glad that I could help!