Lesson video

Hello, everybody.

How are you today? My name is Dr.

Chorich.

I am really excited to be learning with you today.

We are gonna have fun as we move through the learning.

Today's learning is from our unit, measuring length and recording in tables.

The title of our lesson today is Measure Length and Height, Using Centimetres and Millimetres.

We are going to deepen our understanding of how we measure in millimetres and then how we measure in both centimetres and millimetres.

We have some key words that we will be using as we progress through our learning today.

Millimetre, centimetre and difference.

Let's practise those words.

My turn millimetre.

Your turn.

Fantastic.

Well done.

My turn.

Centimetre.

Your turn.

Brilliant.

And the last one.

My turn.

Difference.

Your turn.

Fantastic.

Well done.

And you can see after our keywords, millimetre and centimetre, we have their abbreviations.

So we can write mm for millimetre and cm for centimetre.

And we will be exploring these keywords as we move through the lesson today.

Our learning today will start with looking at measuring length and height in millimetres.

And then we will progress on to measuring length and height in whole centimetres and millimetres.

These are the characters who will help us with our learning today.

We have Laura and Jacob.

So we can decide whether to measure millimetres or another unit like centimetres or metres by estimating the length or height of the object first.

Small objects or small parts of objects such as the width of a pencil's eraser are measured in millimetres.

So if we have a small object, it is measured in millimetres.

Here are some objects that we would measure in millimetres.

I've got the width of a stick, the width of a fingernail, the length of that point on a pencil or the length of the eraser on the end of a pencil.

I wonder if you can think of any more objects that are small that we would measure in just millimetres.

When we measure in millimetres on a centimetre ruler, we need to use the relationship between millimetres and centimetres.

Jacob has remembered this relationship.

He is saying, "There are 10 millimetres in one centimetre," and we can see there are 10 parts from zero to one, there are 10 millimetres.

And Laura has noticed each small interval marked is one millimetre length.

So millimetres are smaller than centimetres because 10 millimetres are needed to make one centimetre.

When we measure the length or height of an object, it is more efficient to start at zero.

That means it's a bit easier really if we start at zero.

So Jacob's saying, "I think the width of the pebble is nine millimetres." Do you agree with Jacob? Has he been efficient and started at zero? Ah, Laura is saying, "I disagree because you have not lined the pebble up with zero." He hasn't, has he? So he has not been efficient.

When we measure the length of the height, we know it's more efficient to start at zero.

And you can see here I have now lined the pebble up with zero and Laura is saying, "Well I started at zero and counted seven interval marks." Can you see how she's counted seven interval marks? So the length of the pebble is seven millimetres.

Well Laura wonders here.

Is there a more efficient way to count in millimetres? What do you think? How could we use that number line to count more efficiently, to count to seven more efficiently? Is there something you might have noticed? And Jacob's gonna prompt us here in our thinking.

"What do we notice about the small intervals marked?" Ah, did you notice this? Laura has noticed that the five millimetre mark is longer.

Do you see how it's slightly longer than the other intervals that are marked? We could use that and count on because we know that is five.

Shall we have a go? So to measure the length of this pebble, we could start at five millimetres and count on.

Five, six, seven.

The pebble is seven millimetres long.

So by using the five millimetre line that's slightly longer, if our object is past that, we can start at five millimetres and count on.

Oh, it's time for you to have a go and check your understanding.

I wonder if you can tell me what number of millimetres the arrow is measuring.

And once you have done that, how do you know? So pause the video and maybe see if you can find someone and tell them the number of millimetres that the arrow is measuring and how you knew.

When you have done that, press Play.

Okay, should we see how you got on? It's pointing to eight millimetres.

How do we know? Well Laura is saying, "I know it's eight millimetres because it is three millimetres further than that five millimetre mark." Can you see that? Is there another way I wonder? Ah, Jacob has noticed it's also two millimetres before the one centimetre mark, which is the same as 10 millimetres.

So it's two millimetres before 10 millimetres, so that's eight millimetres.

I wonder if you knew that and explained that using either one of their ways.

Here's another one to check your understanding.

What is the length of this feather? I've given you a sentence there.

The length of this feather is mm millimetres.

I would like you to pause the video, find someone and say that sentence to them filling in the blank.

When you've done that, press Play.

Okay, what did you say? Did you say the length of the feather is eight millimetres? Because it's three millimetres past that five millimetre mark.

So the length of an object can also be calculated as the difference between the numbers measured at the start and the end of the object.

So we do not have to line an object up with zero, but if we don't, then we need to find the difference.

So the pebble is starting at the longer interval mark.

So that's five millimetres.

So it's not starting and not lined up with zero this time, it's starting at five millimetres.

The end of the pebble is three marks past the one centimetre or 10 millimetre mark.

So this is 13 millimetres.

So to find the length of an object when it's not lined up with the zero, we need to find the difference.

And that is the difference between the numbers measured at the start and the end of the object.

So we've got 13 millimetres and we subtract the five millimetres and that equals eight millimetres.

So the length of that pebble is eight millimetres because the difference between 13 and five is eight.

So the length of the pebble is eight millimetres.

So the length of the object is always the difference between the numbers measured at the start and the end of the object.

However, if we start at zero, it's more efficient because we only have to subtract zero like in our second image.

If we don't start at zero, then we need to find the difference as well.

But this time we'll need to do a subtraction between the numbers that are at the start and end of the object.

So either way, the length of this pebble is eight millimetres.

So now it's time to check your understanding.

Have a think about this, true or false.

The length of this pebble is six millimetres.

So you can see the pebble.

Is that true or false? And then I'd like you to choose a reason for your answer.

Is it because A, the pebble ends at eight millimetres, so it must be eight millimetres long or is it B? The pebble is not at zero.

So we need to find the difference between the start and the end of the object.

This is six millimetres.

So pause the video and when you've said if you think it's true or false and given a reason, press Play.

Okay, shall we see how you got on? So it is true, the length of the pebble is six millimetres, but why is it true? Ah, it's not zero.

So we needed to find the difference.

The pebble ended at eight millimetres, but it started at two millimetres, so we had to subtract the two from the eight, which gave us six millimetres.

We can also measure the length or height of slightly larger objects in millimetres.

And you notice now my ruler has changed.

I'm now using a millimetre ruler.

So the values on here are in millimetres and Laura is reminding us to remember to check that the object is lined up with zero or we will have to find the difference.

And our leaf here is lined up with zero.

So we can just read the number at the end of the object.

The plant is lined up is with zero, and we can see that number at the end is 65.

So the plant is 65 millimetres tall.

It is five millimetres more than the 60.

So it's 65 millimetres.

What about you? Time for you to have a go.

What do you think the length of this leaf is just in millimetres On our millimetre ruler? I've given you a sentence.

The length of this leaf is mm millimetres.

Have a look very carefully and be as accurate as you can.

I'd like you to pause the video, maybe find someone and say that sentence to them filling in the blank.

When you have done that, press Play.

Okay, how did you get on? Did you see that The length of this leaf is 39 millimetres? It's one millimetre before the 40.

And it's really important in maths that we are as accurate as we can be.

So this is one millimetre before 40, so it must be 39 millimetres.

So to find the length or height of an object that does not start at zero, we need to find the difference.

We've learned this earlier in our lesson and this time we are still using our millimetre ruler.

So the start of the ribbon measures 10 millimetres and the end of the ribbon measures 92 millimetres.

So the length of the ribbon is the difference between the start and the end.

So we've got 92 millimetres, subtract 10 millimetres is equal to 82 millimetres.

So the length of this ribbon is 82 millimetres.

So let's check.

By finding the difference, could you calculate the length of this ribbon? So I've given you some sentences to finish off for me by filling in the blanks.

The start of the ribbon measures mm millimetres.

The end of the ribbon measures mm millimetres.

The length of the ribbon is mm millimetres.

Subtract mm millimetres, which is mm millimetres.

So pause the video, have a go.

And when you've calculated the length of this ribbon, press Play.

Okay, shall we see how you got on? Let's have a look.

So the start of the ribbon measures 20 millimetres.

The end of the ribbon is 86 millimetres.

We can see because it's one millimetre past that five.

So it's 85 and one more, 86 millimetres.

And then we have to find the difference.

86 millimetres subtract 20 millimetres is 66 millimetres.

So the length of the ribbon is 66 millimetres.

Okay, it's your turn now to practise and have a go.

So for your first task, I'd like you to use a millimetre ruler and find some objects and measure their length or height in millimetres.

Ask a friend to check your measurements and you could record what you have measured and what that measurement was.

For your second task, I've got a problem for you.

A piece of paper is 90 millimetres long, 35 millimetres is cut from the length of the piece of paper.

How long is the remaining piece of paper? And can you represent this as a bar model? So press pause on the video and when you've had a go at both questions, press Play.

Okay, should we see how you got on? So here are some objects that I found and you might have measured something similar.

I found a pebble and it was 19 millimetres, a ribbon that was 31 millimetres and a feather that was 43 millimetres.

And from a second task I drew a bar model to help me and I know my whole was 90 millimetres.

That's the whole piece of paper.

And I know 35 millimetres was cut from the length of the piece of paper.

So to find the remaining part we need to subtract.

So I have got 90 millimetres, subtract 35 millimetres, which is equal to 55 millimetres.

So the remaining piece of paper must be 55 millimetres long.

Let's now move on to the second part of our learning today.

Measuring length and height in whole centimetres and millimetres.

The length or height of smaller objects can also be given in whole centimetres and millimetres.

So before we were just giving our measures in millimetres.

We're gonna move on and progress that learning to give our measurements in whole centimetres and millimetres.

So what do you notice about the length of this leaf? Jacob has noticed that the length of the leaf is longer than five centimetres, but shorter than six centimetres.

Can you see why he's saying that? That's right.

The leaf has gone past the five on the centimetre ruler, but it's not quite got to the six on the centimetre ruler.

And Laura is saying, "Remember though, we need to check that the object is lined up with zero or we'll have to find the difference." And our object, our leaf is lined up with zero.

So Jacob says, "Well, we know the length of the leaf is more than five centimetres, but not quite six centimetres.

So the length of the leaf is five whole centimetres and three more millimetres." And we write this as five centimetres, three millimetres.

And we tend to use the abbreviations when we're writing the measures, the length or the height down.

So five centimetres, three millimetres because it's five whole centimetres and then three more millimetres.

Let's look at a different object, shall we? Let's look at this feather and we can measure its length in whole centimetres and metres.

And remember, check the object is lined up with zero or we will have to find the difference.

So our feather is lined up with zero.

What do you notice? That's right, Jacob is saying, "The length of the feather is three centimetres and six more millimetres." Can you see why he's saying that? The feather has gone past the three centimetre mark, but it hasn't got to the four centimetre mark.

So it's smaller than four centimetres.

So it's three centimetres and, and it's and six millimetres.

We can tell that because it's one millimetre past that five millimetre mark.

So it's three centimetres and six more millimetres.

The length of the feather is three centimetres, six millimetres.

When we measure in centimetres and millimetres, we always write the measurement in that order and that's really important in maths, okay? So the length of the leaf is five centimetres and three millimetres and we write it in that order.

We wouldn't say the length of the leaf is three millimetres, five centimetres.

We put the larger measurement first.

So the length of the leaf is five centimetres, three millimetres, always in that order.

And here was our feather.

The length of the feather is three centimetres and six millimetres.

Again, we've always written that measurement in that order.

Three centimetres first, then the millimetres, six millimetres.

Let's look at a different object.

We can measure the height of the cake in whole centimetres and millimetres.

So what do we notice? That's right, it is taller than five centimetres, but not quite six centimetres.

And that's exactly what Jacob has noticed.

The height of the cake is five centimetres and two more millimetres.

So the height of the cake is five centimetres, two millimetres.

We've written the centimetre, the whole centimetre measurement first, then the millimetres.

Let's check your understanding.

Can you tell me the length of this brick in centimetres and millimetres? Pause the video.

And when you've worked out the length of the brick, press Play.

Okay, should we see how you got on? The length of this brick is two centimetres, five millimetres, we've got two whole centimetres and then five more millimetres.

Another quiz question for you.

How should we record the measurement of this line? Is it A, eight centimetres and nine millimetres? Is it B, nine millimetres, eight centimetres or is it C, nine centimetres? Press Pause on the video and when you have decided which answer, press Play.

Okay, should we see how you got on? Did you guess A, eight centimetres, nine millimetres? That's correct because we always write the centimetre measurement first and the line has gone past the eight centimetres, but it's not quite got to nine centimetres.

Remember in maths we have to be really accurate.

So C would be wrong because it's not quite nine centimetres.

Now it's your turn to practise.

For question one, I would like you to measure the length of these objects, giving your answer in whole centimetres and millimetres.

You've got a pencil, a pound coin, and a cherry.

For your second question, I'd like to use a 30 centimetre ruler to measure some objects and give your measurements in centimetres and millimetres.

But remember, as Laura is telling us to be efficient and check that the object starts at zero on our ruler.

If it doesn't, that's okay.

You would just need to find the difference.

And for question three, I would like you to work with a partner.

I want you to both draw a line that is between five and six centimetres long, and then measure each other's lines, giving your answer in centimetres and millimetres.

And for the second part, I want you to repeat this for a line that is between seven centimetres and two millimetres, and seven centimetres and nine millimetres.

Pause the video and when you have done all three tasks, press Play.

Okay, should we see how you got on? So for question one, you asked to measure the length of these objects giving your answer in whole centimetres and millimetres.

The pencil was seven centimetres, three millimetres.

The pound coin was two centimetres, five millimetres, and the cherry was four centimetres, seven millimetres.

For question two, these are some objects that you might have measured.

I measured a pebble at two centimetres, six millimetres, a leaf at three centimetres, six millimetres, and a twig at 10 centimetres, five millimetres.

I wonder what you measured.

And for the third question, you might have drawn a line like this.

Your partner will have measured it.

This line is five centimetres, five millimetres long.

And for the second part, you might have drawn a line like this.

Your partner will have measured it.

This line is seven centimetres, four millimetres long.

Fantastic learning today, everybody.

I am really impressed with the amount of progress that you have made in your understanding of measuring lengths and height using just millimetres or centimetres and millimetres.

We have learned that the length or height of objects can be measured in millimetres or in whole centimetres and millimetres.

And we've also learned that it's more efficient to start at zero when measuring.

If the object is not lined up with zero, then the difference needs to be found.

Well done today.