Lesson video

Hello everybody.

My name is Mrs. Johnson.

I am so excited to be here today to help you with some of your maths learning.

I hope you're ready to work hard and have lots of fun.

Let's have a look at what we are going to be learning about today.

This lesson is called Estimate Length in Centimetres.

It comes from the unit numbers 0 to 20 in different contexts.

By the end of this lesson, you will be able to estimate the length of different objects by using known lengths.

Don't worry if you're not sure what that means at the moment because I will help you and we will learn it together.

There are two key words for you to practise in this lesson.

These words are going to be really important for your learning, so I would like you to practise saying them.

It will be my turn first and then your turn.

Ready? My turn, estimate.

Your turn.

My turn, about.

Your turn.

Well done.

At times you might hear that first word said in a slightly different way, so we'll practise saying it that way too.

Last time we said estimate, you might also hear estimate.

Ready? My turn, estimate.

Your turn.

Well done.

There are going to be two parts to this lesson.

To begin with, you are going to learn about identifying known lengths and then in a little while you're going to learn about using known lengths to estimate.

Let's start with identifying known lengths.

There are two friends who are going to help you in this lesson.

Their names are Aisha and Alex.

Listen really carefully because they have lots of important things to share with you today.

Aisha and Alex have been looking for things that are about one centimetre in length.

I wonder what they found.

Let's have a look.

They found the width of a paperclip, the width of a fingernail.

You could have a look at your fingernails now.

Have a look at your nails.

The width of a fingernail.

That's what Alex and Aisha found.

The length of a ladybird.

All of these things are about one centimetre in length.

If they measured them with a ruler, it would be about one centimetre.

Aisha says that, "Using the word about shows that the object might not line up exactly with one centimetre, but it is very close." Let's have a look at that.

Here's our ruler.

If you place the paperclip on the ruler, you can see the width of the paperclip is about one centimetre and the fingernail is about one centimetre and the ladybird is about one centimetre.

All of these things are about one centimetre in length, so if you want to know how long one centimetre is, you can think about some of these things because these are about one centimetre.

Let's check if you can find anything else that could be about one centimetre long.

Do you think it could be a button, a teddy bear or an ice cream? Pause the video and have a think.

Let's see if you are right.

The object that could be about one centimetre long is the button.

This is what you might have been thinking.

This is what Alex says, "I know the width of my fingernail is about one centimetre.

A teddy and an ice cream are much longer than my nail and they could not only be one centimetre, so it must be the button because the other two objects would be too long." Now Alex and Aisha are looking for things that are about 10 centimetres in length.

I wonder what they're going to find this time.

Let's have a look.

The length of a lollipop stick, the height of a toilet roll, and the length from the end of your thumb to the side of your hand, so if you hold your hand up like this, from here to here is about 10 centimetres in length.

If they measured each object with a ruler, it would be about 10 centimetres.

It might not be exactly on the 10, but it would be close.

It will be about 10 centimetres.

Let's have a look at that.

There we can see the ruler is on the lollipop stick and it is about 10 centimetres.

We can place a ruler on the toilet roll to see it's about 10 centimetres and the hand is about 10 centimetres too.

Let's check if you can use that to help you think of one more object that could be about 10 centimetres long.

Do you think it could be a coin, a crayon or a sharpener? Pause the video and have a think again.

This time the object that could be about 10 centimetres long is the crayon.

Well done if you said that.

This is what you might have been thinking.

The height of a toilet roll is about 10 centimetres.

A coin and a sharpener are much shorter than a toilet roll, so they definitely couldn't be 10 centimetres long, so it must be the crayon.

Now it's time for you to practise using those known lengths of one centimetre and 10 centimetres.

I would like you to get some Play-Doh and roll it into a long sausage shape.

Then I would like you to cut it into pieces that are about one centimetre and 10 centimetres long.

You can make lots of pieces but try and get them to be one centimetre or 10 centimetres long.

Use the known length that we've just looked at to help you decide where to cut.

So remember, that the width of your fingernail is about one centimetre long and the length from the end of your thumb to the side of your hand is about 10 centimetres long.

When you've done that work with the Play-Doh, then I would like you to get some strips of paper.

I want you to try and cut one piece of paper that is about one centimetre long and one piece of paper that is about 10 centimetres long.

When you finished, use a ruler to measure each piece of paper and check how long it is, and then I want you to have another go and see if you can improve to get them as close to one centimetres long and 10 centimetres long as you can.

Once you are happy with your strips of paper and you know that they are about one centimetre and 10 centimetres long, I would like you to label them one centimetre and 10 centimetres.

Are you ready? Off you go.

Well done everybody.

Let's have a look at the Play-Doh work first.

This is what your Play-Doh might have looked like so you rolled it into this long sausage shape.

You had to cut it into pieces that were one centimetre long like this, so perhaps your pieces of Play-Doh looked about this size.

Alex says, "I tried to make the one centimetre pieces about the same length as the width of my fingernail." So Alex used his fingernail while he was rolling his Play-Doh and cutting his Play-Doh to help him make sure that they were as close to one centimetres as they could be.

Let's have a look at the 10 centimetre piece that would've looked longer, a bit like this.

Aisha says, "I used the length from the end of my thumb to the side of my hand to help me cut the 10 centimetre piece." Well done to you if you remembered to use your fingernail to help cut the one centimetre pieces and your hand to help cut the 10 centimetre pieces.

Now let's have a look at what your strips of paper might have looked like.

So you should have cut a piece that was one centimetre and a piece that was 10 centimetres.

So perhaps, they looked a little bit like this, a shorter piece and a longer piece.

Then you needed to use a ruler to check, so this is what Aisha did.

She used her ruler to check the one centimetre piece first.

Can you notice anything about Aisha's piece of paper? Aisha noticed that the piece she cut to be one centimetre long was a little bit too long, so she improved her work by making it a bit shorter.

Then she labelled that one centimetre because she was happy with the length of that strip.

Now she knows it's about one centimetre long.

Then she used her ruler to check the 10 centimetre piece.

This time she noticed that it was a little bit too short so she got another strip of paper and tried again and she made it a little bit longer, like this.

And then once she was happy she labelled it 10 centimetres.

Did you use a ruler to check the length of your strips of paper like Aisha did? Did you try again to improve your strips like Aisha? Well done, if you were able to use the ruler to help you have another go and get your strips of paper as close to one centimetre long and 10 centimetres long as you could, very good work.

Now you are going to learn how you can use these known lengths to help you estimate.

Let's have a look at that now.

Alex and Aisha are going to use their known lengths to estimate the length of some other objects.

Alex says that, "Estimate means to think carefully and make a sensible guess." And Aisha says, "You do not use a ruler when you estimate.

You can use the word about to show that it's not an exact measurement." So this means Alex and Aisha are not going to use a ruler.

They are going to make a sensible guess using what they know about one centimetre and 10 centimetres.

Here is Aisha's 10 centimetre strip of paper that she made earlier.

I hope you've got yours ready near you as well because you'll be able to use it in this lesson to help you.

Aisha has this game card.

Aisha has put the game card underneath the strip of paper that is 10 centimetres long and she's noticed something.

I wonder what she's noticed.

Let's have a look.

She says, "I can see that this game card is a bit shorter than 10 centimetres." It's quite close to the end but it is not quite the same length as it as 10 centimetres, it is a bit shorter.

Alex says, "When I place numbers on a number line, I know that 9 is before 10." Do you think that number line might help Aisha to make an estimate of how long this card is? I think it does.

Let's have a look.

Alex knows that 9 comes before 10 on the number line, so Aisha could say my estimate for the length of this game card is about nine centimetres.

Now Alex and Aisha are going to estimate another object.

They're going to look at this eraser.

What do you notice about the length of this eraser compared to the 10 centimetre strip? Let's see what Aisha has noticed.

She can see that it's about halfway along the 10 centimetre strip.

Alex is thinking about a number line again and he says, "When I place numbers on a number line, I know that 5 is halfway between 0 and 10." You can see it here, five is in the middle.

If the eraser is halfway along the 10 centimetre strip, perhaps we could use the knowledge that five is halfway to help with the estimate.

Alex says, "My estimate for the length of this eraser is about five centimetres." Let's check if you can use the 10 centimetre strip to help you estimate how long this domino might be.

There are two estimates.

We're going to look at both of them and I would like you to decide who has chosen the best estimate for the length of this domino? Here's the first one.

"I estimate that the domino is about two centimetres long." Here's the second one.

"I estimate that the domino is about four centimetres long." Pause the video and have a think about who has made the best estimate for the length of this domino.

Well done for thinking carefully about that.

The person who has made the best estimate this time is Alex.

Let's have a think about why Alex has made the best estimate here.

He noticed that the domino is less than five centimetres long.

Aisha and Alex both gave an estimate that was less than five centimetres long, so why might four centimetres be a better estimate than two centimetres? I think it might be to do with how close it is to that five.

What do you think? Let's have a look.

Aisha says, "The position on the number line is close to five, so now I think that four centimetres is a better estimate than two centimetres." She's right, isn't she? The domino is quite close to the five and on a number line four comes before five, so four centimetres is a better estimate than two centimetres.

Alex and Aisha want to estimate the length of this leaf and they've placed it along the 10 centimetre strip.

They've also started to place a number line underneath to help them think about how long this leaf might be.

Alex has noticed that the leaf is a bit longer than five centimetres.

He knows that because five centimetres is halfway, it's in the middle and this leaf is a little bit longer than that, isn't it? He also knows that six is the number after five on a number line, he's going to show that here.

You can see five in the middle of the number line and you can see that the leaf is just a little bit longer than that so he knows that six is the number after five on the number line.

That means Aisha can say, "I estimate that this leaf is about six centimetres long because five plus one is equal to six." Now let's have a look at how they're going to estimate the length of this feather.

Alex has noticed that the bit after five is more this time.

Let's have a look at that on the number line.

The bit after five is more this time, isn't it? When they estimated the leaf it was only a little bit past the five.

This time it has gone more past the five, but Alex has noticed something else that's important.

It is still closer to 5 than it is to 10 on the number line.

That means Aisha can say, "I estimate that this feather is about seven centimetres long because five plus two is equal to seven." Let's see what's going to happen when they estimate the length of this block.

Alex has noticed that the bit after five is more again now it is closer to 10 than it is to 5 on the number line.

Let's have a look at that.

So Alex is noticing that the end of the brick is now closer to the 10 than it is to the 5.

That is going to help Aisha to make her estimate so she can say, "I estimate that this block is about 8 centimetres long because 8 is closer to 10 than it is to 5." Alex has noticed something else.

He thinks that the bit after five could be three because five plus three is equal to eight, so eight centimetres looks like a good estimate for this block.

Let's see if you can match up these estimates to these Play-Doh snakes.

Look carefully at each Play-Doh snake, it has a 10 centimetre strip and a number line to help you.

Then look carefully at the three estimates that are at the bottom.

I will read them to you and then I want you to pause the video and see if you can match them up.

The first one says, I estimate that this snake is about four centimetres long because four is one less than five.

The second one says, I estimates that this snake is about seven centimetres long because five plus two is equal to seven and the last estimate says I estimates that this snake is about eight centimetres long because five plus three is equal to eight.

Pause the video and have a really good think about which estimates match each Play-Doh snake.

Well done.

You have thought really carefully about this.

Let's have a look and see if you have matched them up correctly.

The first Play-Doh snake should match with the estimate that says, I estimates that this snake is about seven centimetres long because five plus two is equal to seven.

We can see, this Play-Doh snake is five and a bit but the bit after the five is not that long so seven centimetres would be a good estimate because we can see that it looks like it could be five plus two to equal seven.

The second Play-Doh snake matches the third estimate.

I estimate that this Play-Doh snake is about eight centimetres long because five plus three is equal to eight.

If you look at the bit after the five you can see that on this Play-Doh snake, that bit is longer than the first one so that is why the best estimate for this one is eight centimetres because it is five and a bit and the bit looks like it could be three.

Five plus three is equal to eight.

The last Play-Doh snake matches the first estimate.

This one is about four centimetres long because four is one less than five.

You can see on the number line that this Play-Doh snake is a little bit shorter than five centimetres, so four centimetres is a good estimate here.

Now it is time for you to go and do a little bit more practise.

You are going to try and do some estimating length.

There are going to be some pictures of some Play-Doh snakes and I would like you to try and estimate how long you think they are.

This is the first Play-Doh snake that you are going to estimate look really carefully at the 10 centimetre strip and the number line to help you.

I would like you to use this sentence to explain your thinking to a partner or to an adult who is near you.

I estimate that snake is about mm centimetres long because mm.

Maybe you can talk about five and a bit or you might talk about something that's a little bit more than or a little bit less than.

Maybe you can talk about what you know about numbers on a number line.

Then you're going to look at the second snake, this one and again explain your thinking to a partner using the same sentence as last time.

When you have done that you can get some more of your own Play-Doh and see if you can make some of your own Play-Doh snakes.

I would like you to try and estimate how long you think each Play-Doh snake is.

You can use your 10 centimetre strip of paper from earlier to help you to do this.

Are you ready to go and try? Off you go.

Well done everybody.

That was some really good estimating.

This is how Alex estimated the length of the Play-Doh snake.

Wonder if you did something similar to this.

Alex said, "I estimate that this snake is about nine centimetres long because it is only a little bit shorter than 10 centimetres and I know that 1 less than 10 is 9." Alex used his knowledge of numbers on a number line, didn't he? To help him remember that 9 comes before 10 so 9 centimetres would be a good estimate.

Did you make any Play-Doh snakes that were close to 10 centimetres long? A little bit like this one? I wonder if you did.

The second Play-Doh snake that you had to estimate was this one.

This is what Aisha said.

I wonder if your thinking was similar to this.

Aisha said, "I estimate that the snake is about six centimetres long because it is only a little bit longer than five centimetres and I know that six is equal to five plus one." Aisha has used her knowledge of five and a bit numbers and she knows that five and a little bit more could be six because five plus one is equal to six.

Did you use five and a bit to help you work out how long any of your Play-Doh snakes were like Aisha did? Well done if you were thinking about five and a bit.

That's really helpful when you are estimating length.

Now that you are at the end of the lesson, you have learnt some known length today.

You know that the width of a paperclip, the length of a ladybird and the width of your fingernail are all about one centimetre in length.

You have also learnt about some things that are about 10 centimetres in length.

The height of a toilet roll, the distance on your hand from your thumb to the side of your hand, and the length of a lollipop stick.

You have learn how you can use those known lengths to help you estimate the length of an object.

And you know that when you estimate you don't use a ruler, you think about known lengths and you make a sensible guess.

You have also learned to use your knowledge of number lines to explain how you chose your estimate.

You have worked really hard in this lesson and done lots of really good thinking today.

Well done.

I hope that I will see you again soon for some more maths learning.

Bye everybody.