Lesson video

Hello.

How are you today? My name is Dr.

Shorek, and I am delighted that you have chosen to complete this learning with me.

We are gonna have a lot of fun as we move through the learning together.

Today's lesson is called converting between centimetres and millimetres.

We are going to deepen our understanding of how we can change from one unit of measure to the other.

Sometimes new learning can be a little bit tricky, but I'm here to guide you.

And if we work really hard together, I know that we will be successful.

So how do we convert between centimetres and millimetres? So these are the keywords that we will be referring to as we progress through our learning.

We have equivalent and convert.

My turn: equivalent.

Your turn.

Fantastic.

My turn: convert.

Your turn.

Brilliant, well done.

So look out for those words as we move through our learning.

So the keywords that we are going to be referencing today are when something is equivalent, it is equal in value.

And you will see that as we move through the learning, how we are going to notice that something in centimetres can have the same length as something in millimetres.

And that is changing from centimetres to millimetres or millimetres to centimetres.

And when we change the unit of measure, we call it converting.

So we are going to start our learning today on converting between millimetres and centimetres.

We have Laura and Jacob who are going to help us today.

I am showing you a representation of a 15-centimeter ruler.

I wonder if you might have one like this near where you are now that you could look at.

Or maybe you have a 30-centimeter ruler near you.

Or if you don't, you might like to pause the video and go see if you can find one and then press play.

So what do you notice about millimetres? And remember, millimetres are those small marks in between the whole centimetres.

What do you notice about them? Maybe tell someone near you what you notice.

Shall we see what Laura noticed? Laura noticed that 10 millimetres are the same length as one centimetre.

What about Jacob, do you think? Jacob noticed that 20 millimetres are the same length as two centimetres.

Did you notice that? I wonder what else you might've noticed.

We can use the relationship between one centimetre and 10 millimetres to help us convert between millimetres and centimetres.

So that means to change between the two units of measure.

So Laura noticed that if one centimetre length is the same as 10 millimetres, then, and Jacob can expand on this and say two one-centimeter lengths must be the same as 20 millimetres.

Ooh, what do you think might come next, any thoughts? That's right, so three one-centimeter lengths must be the same as 30 millimetres.

And you can see that represented.

We've got one centimetre is the same as 10 millimetres.

Two one centimetres is the same as 20 millimetres.

And three one centimetres are the same as 30 millimetres.

Because each one-centimeter length is the same as 10 millimetres.

We are learning that 10 one-millimeter lengths are the same as one centimetre.

We could also say that there are 10 one-millimeter lengths in one centimetre.

And if we zoom in on this part of the ruler, we can clearly see those 10 one-millimeter lengths being the same as one centimetre.

Jacob is saying one millimetre is smaller than one centimetre.

What do you think? Do you agree with Jacob? Yes, that's right.

One millimetre must be smaller than one centimetre, because 10 one millimetres make up one centimetre.

So there are 10 millimetres in one centimetre.

We know that now.

I can represent this in a bar model to show that one centimetre and 10 millimetres are equal.

So one centimetre and 10 millimetres are equivalent in length or height.

They are the same length or height.

So we can show this on a number line that one one centimetre is equivalent to 10 millimetres.

What else do we know then? That's right, we know that two one-centimeter lengths are equivalent to 20 millimetres.

Three one-centimeter lengths are equivalent to 30 millimetres.

Hmm, I wonder what might come next.

Do you know? Did you get that that four one-centimeter lengths would be equivalent to 40 millimetres? Let's see what comes next.

Fantastic, there we go.

So now, we know that 10 centimetres is equivalent to 100 millimetres.

Let's look at this in a different way.

So if one centimetre equals 10 millimetres, what else do we know? That's right, we know two centimetres equals 20 millimetres.

Three centimetres equals 30 millimetres.

What's gonna come next, do you know? That's right, four centimetres equals 40 millimetres.

And next? That's right, let's keep going.

And finally, we're going to have 10 centimetres equals 100 millimetres.

We can work out all those facts from knowing one centimetre equals 10 millimetres.

So we can measure the length or height of objects in one unit, for example, centimetres, and then convert or change to a different unit, such as millimetres.

So I've got my leaf here, and Laura is reminding us that we should always estimate the height or the length of the object first, so we know which measuring equipment to use and which units to use.

And estimating also helps us to check that our measurement is reasonable.

Jacob is saying, "I think the length of the leaf is less than 10 centimetres.

So we should measure in centimetres or millimetres." We wouldn't measure in metres, would we? Because metres are used to measure longer or taller objects, so I agree with Jacob.

I think we should measure in centimetres or millimetres.

Let's measure the leaf in centimetres.

The leaf is five centimetres long.

So we can use our learning about the relationship between one centimetre and 10 millimetres to help us to convert the five centimetres into millimetres.

So always worth checking, our length is near to the estimate, so we know we are accurate.

And let's have a look now.

I'm representing the length of my leaf in a bar model.

Five centimetres is the whole length of the leaf.

And five centimetres is made up of five one-centimeter lengths.

Hmm, I wonder if you can guess why I've split the five into five one-centimeter lengths.

That's right, it's because we know one centimetre is equal to 10 millimetres.

That's the key fact that we have learned.

So I can then represent each centimetre as a 10 millimetre.

So five centimetres is equal to five of those 10-millimeter lengths.

And that means then that five centimetres and 50 millimetres are equivalent.

So the height of my leaf or the length of my leaf is five centimetres, or we could convert to millimetres and say that it is 50 millimetres.

Five centimetres and 50 millimetres are equivalent.

So let's check your understanding so far.

Which pebble is longer? Pebble a is three centimetres.

Pebble b is 30 millimetres.

And pebble c, I'm sorry, option c, they are both the same.

So which pebble is longer? Pause the video.

Have a think and press play when you think you know.

Okay, should we see how you got on? Which pebble was longer? Ah, that's right.

Jacob is saying they are both the same.

Three centimetres is equivalent to 30 millimetres.

Three centimetres is made up of three one-centimeter lengths.

Each one-centimeter length is 10 millimetres.

So three centimetres must be equivalent to 30 millimetres.

The pebbles were the same length.

So another question to check your understanding now.

I want you to complete the sentence by converting the length of the feather from centimetres into millimetres.

So the feather here, you can see is nine centimetres.

And I've given you a sentence to complete: Nine centimetres is equivalent to um millimetres.

Press pause, and when you think you know, press play.

Okay, how did you get on? Did you realise that nine centimetres is equivalent to 90 millimetres? Nine centimetres is made up of nine one-centimeter lengths.

Each of those one-centimeter lengths is the same as 10 millimetres.

We've got nine 10 millimetres, which is 90 millimetres.

Well done.

So it's your turn to practise now.

So for task A question one, I would like you convert these lengths between millimetres and centimetres.

So using that key fact that we've been learning, one centimetre is equal to 10 millimetres, can you convert these lengths? Question two: I would like you to tick the objects that have a total length of 10 centimetres.

And then, can you challenge yourself to find a different set of objects that have a total length of 10 centimetres? And question three: A ribbon is 80 millimetres long.

A dressmaker cuts three centimetres off the ribbon.

I'd like you to represent this question as a bar model.

And I want you to tell me what is the length of the ribbon now, and can you give your answer in millimetres? And then, what is the length of the ribbon now, but giving your answer in centimetres? When you've finished all three questions, pause the video, sorry, and when you've finished all three questions, press play.

Okay, shall we see how you got on? Question one: You were asked to convert these lengths between millimetres and centimetres.

Three centimetres is equal to 30 millimetres.

30 millimetres is equal to three centimetres.

And going across, 20 millimetres is equal to two centimetres.

So two centimetres must be equal to 20 millimetres.

I wonder if you noticed that they were just swapped around.

And then we've got seven centimetres is equal to 70 millimetres.

Eight centimetres is equal to 80 millimetres.

Nine centimetres is equal to 90 millimetres.

We've got 40 millimetres is equal to four centimetres.

50 millimetres is equal to five centimetres.

And 60 millimetres is equal to six centimetres.

Well done.

And for question two, you were asked to tick objects that have a total length of 10 centimetres.

And then you were asked to do that again, see if you could find another set.

This is one set that I found.

The leaf is five centimetres, and the pebble is 50 millimetres.

So five centimetres is equal to 50 millimetres.

If I added those two together, they would have a total length of 10 centimetres.

So that's one set of objects you might have ticked.

And for my second set of objects, I found the green leaf, the conker, and the feather.

Those objects had a total length of 10 centimetres.

Well done.

And for our final question, question three, we've got a ribbon was 80 millimetres long.

The dressmaker cuts three centimetres off the ribbon.

You were asked to represent this in a bar model first.

So 80 millimetres is my whole ribbon.

Three centimetres was cut off the ribbon.

Then you were asked to tell me what length of ribbon is left in millimetres and in centimetres.

So the length of the ribbon now is 50 millimetres, or we could also say it is five centimetres.

50 millimetres is equal to five centimetres.

They are equivalent lengths.

Okay, fantastic learning so far, everybody.

Let's move on now and really deepen our understanding about how we convert between centimetres and millimetres.

And in particular, we're going to look at how we convert between just millimetres and measurements that have been given in centimetres and millimetres.

So we're gonna think about this snail and think about what the length of this snail is.

And Laura is reminding us we should estimate the height or length first, so we know which units to use and to check that our measurement is reasonable.

Jacob is saying that he thinks the length of the snail is less than five centimetres, so we should measure in centimetres or millimetres.

Do you agree? Yes, I think I agree, because metres measure longer and taller things.

And a snail is quite small.

So our snail is longer than two centimetres but shorter than three centimetres.

So how do we give an accurate measurement? Ah, that's right, we could use whole millimetres.

So the length of the snail is 23 millimetres.

We can see it because the snail is lined up with zero, and the snail ends at 23 millimetres.

But what if I wanted to convert the length of the snail so that we gave the measurement in centimetres and millimetres? Ah, Jacob is saying, "We can use partitioning to help us." 23 is made of 20 and three.

So 23 millimetres must be made of 20 millimetres and three millimetres.

And we can use that to help us convert from millimetres to centimetres and millimetres.

The length of the snail is about 23 millimetres.

And we can use partitioning to help us convert to whole centimetres and millimetres.

So 23 is made of 20 and three.

And we know that 20 millimetres is equal to two centimetres.

So 23 millimetres is equivalent to two centimetres three millimetres.

They are equal.

23 millimetres equals two centimetres three millimetres.

So that means the length of the snail is both 23 millimetres or two centimetres three millimetres.

Those lengths are equivalent.

So let's use partitioning and the relationship between millimetres and centimetres, remember, one centimetre is equal to 10 millimetres, and let's use that relationship to help us convert from 68 millimetres to centimetres and millimetres.

So I've represented my 68 millimetres in a bar model.

First we need to partition.

68 is made from 60 millimetres and eight millimetres.

And we know 60 millimetres is equal to six centimetres.

So 68 millimetres is equivalent to six centimetres eight millimetres.

68 millimetres equals six centimetres eight millimetres.

Let's have another practise.

Let's use partitioning again to convert 92 millimetres to centimetres and millimetres.

So 92 millimetres is made from 90 millimetres and two millimetres.

And we know 90 millimetres is equal to nine centimetres.

So 92 millimetres must be equivalent to nine centimetres two millimetres.

They are equal.

92 millimetres is equal to nine centimetres two millimetres.

92 millimetres and nine centimetres two millimetres are the same length as each other.

They are equivalent.

Just one is given in just millimetres.

The other measurement is given in centimetres and millimetres.

Let's check your understanding.

I want you to use partitioning to convert 47 millimetres to centimetres and millimetres.

So I've given you some sentences to help.

47 millimetres is made up of um millimetres and um millimetres.

And then what's that fact that you know? Um millimetres equals um centimetres.

So 47 millimetres is equivalent to um centimetres um millimetres.

So 47 millimetres equals um centimetres um millimetres.

So pause the video.

Have a go and when you're ready, press play.

Okay, how did you get on? Did you work out that 47 millimetres is made up of 40 millimetres and seven millimetres? And 40 millimetres is equal to four centimetres.

So 47 millimetres is equivalent to four centimetres seven millimetres.

Or we could also say 47 millimetres equals four centimetres seven millimetres.

So we can also convert measurements given in centimetres and millimetres to just millimetres.

We can do it the other way around.

So I've got a mouse here.

And the height of that mouse is four centimetres six millimetres.

And Jacob is saying, "I wonder what the height of this mouse is in just millimetres? Let's convert." So we know one centimetre is equivalent to 10 millimetres.

And Laura is saying, "Well, we've got four centimetres, so that must be equivalent to four 10-millimeter lengths.

And that's 40 millimetres." So four centimetres equals 40 millimetres.

And we have six millimetres more.

So four centimetres six millimetres is equivalent to 46 millimetres.

So let's represent this as a bar model.

You can see my whole is the height of the mouse in centimetres and millimetres.

And we want to convert this to millimetres.

So we're gonna partition.

So I've got my four centimetres and my six centimetres.

And we're going to use that relationship between centimetres and millimetres.

We know four centimetres is equal to 40 millimetres.

And then, I can recombine, so I've got 46 millimetres.

So four centimetres six millimetres is equivalent to 46 millimetres.

Four centimetres six millimetres equals 46 millimetres.

So both of those measurements are the same height or length.

So we could say our mouse is four centimetres six millimetres tall, or we could say it is 46 millimetres tall.

So I'm going to show you how to do one of these, and then I want you to have a go on your own.

We're going to convert six centimetres three millimetres to just millimetres.

So six centimetres is the same as 60 millimetres.

And then I've got the additional three.

So that equals 63 millimetres.

So six centimetres three millimetres equals 63 millimetres.

So using my model structure, I'd like you to have a go at converting five centimetres nine millimetres to millimetres using the same structure.

Have a go, and when you're ready, press play.

Okay, how did you get on? Did you manage to work out that five centimetres is the same as 50 millimetres? 50 millimetres and the additional nine millimetres is equal to 59 millimetres.

So five centimetres nine millimetres is equal to 59 millimetres.

Well done.

So converting between units can be used to solve problems. Which mouse is taller, do you think? We've got the white mouse is four centimetres five millimetres.

And we've got the grey mouse, which is 43 millimetres.

Which mouse is taller? Hmm, but also, what do you notice? Do you notice that the units are different? The white mouse, the height has been given in centimetres and millimetres.

The grey mouse, just been given in millimetres.

So the units are different, so we need to convert one of the units to be the same as the other, then we can compare it more easily.

So let's convert four centimetres five millimetres to millimetres.

So there's my whole amount, four centimetres five millimetres.

I can partition, and we know four centimetres is equal to 40 millimetres.

And I've got five extra millimetres, so four centimetres five millimetres is equal to 45 millimetres.

Four centimetres five millimetres is equivalent to 45 millimetres.

They are equal in length or height.

So which mouse is taller? Well, we converted the height of the white mouse.

Four centimetres five millimetres is equal to 45 millimetres.

And we can see now that the grey mouse is 43 millimetres.

Which mouse is taller then, do you think? That's right, the white mouse is taller.

It's two millimetres taller.

The white mouse is 45 millimetres, and 45 is two more than 43.

We could also have converted it the other way around, though, so let's have a go at that, shall we? We can convert 43 millimetres to centimetres and millimetres.

So let's have a look.

If 43 millimetres is my whole, I can partition that to 40 millimetres and three millimetres.

And we know 40 millimetres is equal to four centimetres.

So I can see here that 43 millimetres is equivalent to four centimetres three millimetres.

43 millimetres equals four centimetres three millimetres.

They are the same length.

So let's look at our problem about which mouse is taller.

If we converted the height of the grey mouse this time, 43 millimetres equals four centimetres three millimetres.

So which mouse is taller? Is the white mouse still taller? Yes, it is.

It's two millimetres taller.

Whichever unit of measure we chose to convert from or to, we arrived at the same answer, the white mouse is taller.

So it does not matter which way you convert, from millimetres to centimetres and millimetres or from centimetres and millimetres to millimetres, but it is important that we do convert one of them so that the units of measure are the same.

And then it makes it easier for us to compare.

So let's check your understanding.

Which twig is longer? Twig a is six centimetres four millimetres.

Twig b is 67 millimetres.

And twig c, if you're not sure.

Oh sorry, it's not twig c, is it? Just option c, I'm not sure.

Have a think, press pause, and when you're ready, press play.

Okay, how did you get on? Did you work out that twig b is the longest at 67 millimetres? We could convert the twig a measurement.

Six centimetres four millimetres is equivalent to 64 millimetres.

And 64 millimetres is shorter than 67 millimetres.

So twig b was longer.

Your turn to practise now for task B.

Question one: Which leaf is longer? And explain how you know.

So the brown leaf, five centimetres three millimetres, or the green leaf at 53 millimetres? Question two: Can you insert the symbols smaller than, greater than, or equals to make these calculations correct? And question three: Can you determine which mouse is taller by converting one of them to the same unit? And how much taller is the mouse? Could you give your answer in millimetres? So you've got three questions to have a go at.

Press pause at the video.

When you've had a go at all three, press play.

Okay, shall we see how you got on? Question one, you were asked which leaf is longer and to tell me how you know.

Well, both leaves are the same length.

Did you spot that? Because five centimetres three millimetres and 53 millimetres are equivalent.

They are the same length.

Well done if you spotted that.

And question two.

You were asked to insert the symbols to make the calculations correct.

27 millimetres is equal to two centimetres seven millimetres.

And that means then that two centimetres seven millimetres must be equal to 27 millimetres.

If we go across, 32 millimetres is less than three centimetres four millimetres.

So that means that three centimetres four millimetres must be greater than 32 millimetres.

One centimetre four millimetres is less than 15 millimetres, because one centimetre four millimetres is equivalent to 14 millimetres.

53 millimetres is less than six centimetres, because six centimetres would be 60 millimetres.

Four centimetres five millimetres, well that's equal to 45 millimetres.

They are equivalent.

20 millimetres is less than two centimetres three millimetres, because that would be 23 millimetres.

Nine centimetres one millimetre is greater than 90 millimetres, because nine centimetre one millimetre would be 91 millimetres.

And 87 millimetres is smaller than 90 millimetres.

I wonder how you got on.

Well done.

And question three, you were asked to tell me which mouse is taller by converting to the same unit and then to tell me how much taller that mouse is.

I chose to convert the 46 millimetres, and that was equivalent to four centimetres six millimetres.

So I can see that four centimetres six millimetres is greater than four centimetres five millimetres.

So that brown mouse is taller.

And it's taller by one millimetre.

Well done.

Fantastic learning today, everybody.

I hope you have really deepened your understanding of how we can convert between millimetres and centimetres.

And now you know how to do that.

You know how to convert between millimetres and centimetres, but also, between millimetres and centimetres and millimetres.

So really great progress today.

We've learned to convert between centimetres and millimetres, we can use the relationship between one centimetre and 10 millimetres.

We've learned that to convert between millimetres and centimetres and millimetres, we can use partitioning to help us.

And we also know always to think about estimating the length or height of an object, because it helps us to decide which unit to use when measuring and it helps us to know if our measurement is accurate.

Really well done.