About this video
The video finds the volume of a figure built from unit cubes by breaking it into simpler parts. First it splits the figure into a 4 by 4 by 2 rectangular prism (32 cubic units) and a small 2 by 2 by 1 piece (4 cubic units). Then it checks by counting the 18 cubes in one layer and doubling, getting 36 cubic units both ways.
You'll be able to
- find the volume of a figure by breaking it into rectangular prisms and adding their volumes.
- find the volume of a rectangular prism by multiplying length times width times height.
- check a volume a second way, such as counting cubes in one layer and multiplying by the number of layers.
Key words
- unit cube
- A cube that is 1 unit long, 1 unit wide and 1 unit high; it has a volume of 1 cubic unit.
- volume
- How much space a solid figure takes up, measured in cubic units.
- rectangular prism
- A box-shaped solid with six rectangle faces.
- cubic units
- The units used for volume; each one is the space of one unit cube.
Transcript
- [Voiceover] So these are two pictures of the same figure. This is a front view of the object, and this is the back view of the object. And if a unit cube looks like this, what I want to do is I want to figure out the volume of this figure in terms of unit cubes, or in terms of cubic units.
I encourage you to pause the video and think of it on your own before we try it together. All right, well, there's a bunch of ways that we could tackle this, all of them kind of breaking this figure up in different ways. One way we could do it, we could break it up into this.
I guess we could call it a rectangular prism. So, if you could see through there, it would be like this, so this piece right over here, this piece right over here. And I'll redraw it here, so you can visualize it. So, if I were to redraw it, it looks like this.
It looks like this. And what are its dimensions? Well, its four units wide. It's two units high. And then it's four units, we could say long, or four units deep. So just like that. So what's the volume of this yellow part? Well, the volume is just you multiply these three dimensions, the length times the width, times the height.
So the volume is going to be our length times our width times our height. Four times four is 16 times two is 32. But we're not done. That's just the volume of this yellow part. We still have to take into consideration the volume of this piece right over here that we haven't figured out yet, this piece right over there.
Now, this one might just jump out at you. You could just count the unit cubes, but I'll redraw it here, just to show you what's going on. All right. So it looks like this. It looks like this. And what are its dimensions? Well, it's two wide, two high, and we could say one deep or one long.
So its volume is going to be equal to your length times your width times your height, which is equal to four. And you just see that. There's one, two, three, four unit cubes in this object. So the total volume is going to be 32 plus 32 plus four is equal to 36.
Now, of course, there's other ways to tackle it. You could just say, hey, let's figure out the volume of the blue layer and then just double it because that red layer has the same volume as the blue layer. And the blue layer, you could, say, well, look, it's only one deep.
So we just have to count the cubes up here, and then we'll know how many unit cubes fit into it. So you literally could just count one, two... Let me do it a color you can actually see. You just have to go one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18.
So you see there are 18 cubes in the blue layer, and there are going to be another 18 in the red layer, plus 18, that also gets you to 36 unit cubes, or a volume of 36 cubic units.
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