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### Course: 3rd grade foundations (Eureka Math/EngageNY) > Unit 2

Lesson 1: Topic A: Foundations# Measuring lengths (cm, m)

Sal measures objects with a ruler.

## Want to join the conversation?

- what does dimension mean(11 votes)
- 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.(21 votes)

- is measureing your backyard in meters unusual?(11 votes)
- 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.(16 votes)

- Lets say something had a negative length. What would that mean? Or maybe, what would that look like?(7 votes)
- I don't believe that a negative length is possible. It's a little hard to explain. Length is how long something is, so you can only work with positive numbers, because you sort of "count" how long something is, like how many inches long. When you count you have to start at 0, and move up from there. If it were possible, I have no idea what it would look like. I guess that's something to think about :) It's a difficult concept to understand, but I hope I helped a little bit.(3 votes)

- How much bigger is an inch form a centimeter? Is it about 2.6 times bigger?(5 votes)
- an inch is 2.54 times a centimeter.(5 votes)

- How did he get eight meters? did he round and if so why? it didn't say to round so I am terribly confused! plz help me someone because I want to pass this math.(4 votes)
- Sal used the ruler to measure the garden. First, he needed to line up the corner of the ruler with the corner of the garden. If the ruler is crooked, the measurement will not be accurate. He did not need to round the answer because the garden lined up just about perfectly.(6 votes)

- Can it be like one side is inches and one side is a foot?(4 votes)
- Yes. For example, say that one side of a triangle is 24 inches, another side is 2ft and the last side is 1 foot. Then, turn 24 inches into feet. There are 12 inches in one foot, so 24 inches is 2ft. Therefore, the sides of the triangle are equal to 2ft, 2ft, and 1 foot(5 votes)

## 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.