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## 3rd grade foundations (Eureka Math/EngageNY)

### Unit 4: Lesson 1

Topic A: Foundations

# Measuring lengths (cm, m)

Sal measures objects with a ruler.

## Want to join the conversation?

• what does dimension mean
• Dimension in math can be expressed in three dimensions. It is the way a figure is represented and measured. The first dimension is a one dimensional line, (1D) which only has length and height. The second is a two dimensional plane (2D), which has height, length, but area. An example of this would be a shape like a square. Finally, a three dimensional figure (3D) has length, height, and depth, and surface area. Think of a three dimensional figure as an object that looks like you can hold it. Examples of three dimensional objects are cubes, spheres, and much more.
• is measureing your backyard in meters unusual?
• It depends! If you live in America, Liberia, or Myanmar, you are more likely to measure it in feet or yards. However, people in other countries measure things in meters.
• how do you get to your mison
• What's the longest dimension of measurement?!
• 1 inch is how many centimeters?
• If you are rounding up to the nearest centimeter, then it would be 3cm. If you are wanting to know the exact amount then it is 2.54cm.
• how to take a brain fitness test
• can i used a ruler to measure things
• Yes, rulers were made to measure things.
• why do i need to ask a question?
• bscouse we will be smart
• What is 2/3 of a meter long
• I am learning a lot from home right now and khan academy has been a really good resource to use at home
to learn like math and things like that and i have been
learning and growing with things i would need help at school and when we get back to school i hope that i will grow a lot more and be better in math in 5 grade so thanks khan academy fro all that you do it help me a lot thanks.

## Video transcript

- [Voiceover] Which shows the length of the rectangle measured correctly? Alright. So here, we have this green rectangle, and, let's see, how did we measure it? We have one centimeter, right over here, and then we put another centimeter right over here. And they say, "Two rulers "measure the rectangle side-to-side." Well this makes sense, 'cause we can say, "Look, if from here to here, from the beginning "of the rectangle to the middle, is one centimeter, "and then it's another centimeter that "gets us to the other side, to the right side, "then we know that this is going to be "two centimeters long." One, and two. So I'm pretty sure this is measured correctly. But let's just make sure that the other two don't really measure the rectangle correctly. So this one right over here, you have one centimeter and then another centimeter, but you're leaving a gap right over here. And you can't leave a gap here, you wanna measure what this distance is. And you notice that this ends to the right of the right of the rectangle. So this isn't a good way of measuring it. And this way, you're not going all the way, the entire length of the rectangle, so this, you're coming up short. You need to measure the entire length. You need to start on the left side, which they did, but you need to go all the way, without any gaps, and without overlapping the rulers in any way to get to this side. So this isn't right either. So let's keep doing these. Which shows the length of the eraser measured correctly? So, this one, well once again, there's some weirdness over here, I don't even know what's happening. But the entire ruler isn't even getting to the entire length of this rectangle. So this isn't measured correctly. And they say, "Two rulers measure the eraser and overlap." Oh, I see, this is kind of, the ruler's a little bit transparent, so this one is overlapping with the one underneath. So you definitely don't wanna do that. You wanna put them right next to each other without a gap. And you wanna get all the way to the edge of this rectangle. So this one, you have a gap, and you're actually going beyond the edge of the rectangle. So that's not good. Here, you have no overlap, and no gap right over here. They're just right next to each other. And we're starting at the left side of this rectangle. And we're going exactly to the right side. We're not overstepping it or we're not under-doing it. So this is going to be right. This is a lot of fun. Let's do, okay this is interesting. What is the length of the floor of the bank, in meters? This is a picture of a bank. I guess this is the big money in the bank (laughs). Those are big dollar bills, and those are big coins. Drag the ruler to make the measurement. And this is in meters, so I can click on this, and then I can put it, remember I wanna, I don't wanna do this, this would be wrong, because I wanna start measuring right at the edge, right at the edge of the bank. So I wanna do it like that. And I see, okay, the length of the bank, well how much is that? Well you see this right wall right over here, it's right at four, right at four meters. So this is going to be four meters long. Let's do another one. What is the length of Maria's back yard in meters? Drag the ruler to make the measurement. So once again, you don't wanna do something like this, where you're starting to measure, before the garden even starts or you're starting to measure too late. You wanna measure right at the edge, right over there. So that's where the guard starts, so that's where your ruler should start, measuring one, two, three, four, five, six, seven, eight, looks pretty close. Let's see, it looks pretty close to eight, eight meters right over here. So, yea, this length of this is eight meters. Looks pretty close, I'll say eight. Alright, let's do one more of these. What is the length of the tray of cookies in centimeters? Now when they say "length," they mean the longest, "length" actually means the longest dimension. If you have a width and a length. And so the longest dimension of a tray of cookies is gonna be this side right over here. You don't wanna measure, you don't wanna measure that side up there, that would not be the length. The length, if people don't tell you otherwise, it's the longest dimension. So we wanna measure, so we wanna measure, let me make sure I don't lose my ruler. We wanna measure, we wanna measure along the top or along the bottom. And we see that it is, once again, we don't wanna do this, that would be starting the ruler too far to the left, and you don't wanna do this, starting the ruler too far to the right, you wanna put it right at the edge, right over there. My ruler isn't perfectly straight. And we see that this cookie tray is, it is right at about eight centimeters. Eight centimeters. And we're done.