Lesson video

Hello everyone, and how are you today? My name is Dr.

Shorack, and I am really excited to be learning with you today.

We're gonna have a lot of fun as we progress through the lesson.

Today's lesson is from the unit Measuring Length and Recording in Tables.

This lesson is called Measure Length and Height Using Whole Metres and Centimetres.

As we move through the learning today, we're gonna think deeply about how we can measure efficiently and how we make a decision as to when we measure in centimetres or metres.

These are the key words that we will come across as we move through our learning today.

Got metre, and in brackets after the metre, is the letter M.

This is because we can abbreviate the word metre with an M.

So when we see M in this lesson, we'll know it means metre.

And we've got centimetre, and it's the same with centimetre.

We can abbreviate centimetre to cm.

And we've got the word difference.

So let's practise those words.

So my turn, metre.

Your turn.

Fantastic.

My turn, centimetre.

Your turn.

Lovely.

And my turn, difference.

Your turn.

Fantastic.

Well done.

So these are the keywords that we're going to be exploring as we move through our learning today.

So our learning today is about measuring length and height using whole centimetres and metres.

We are going to start off by thinking about measuring by starting at zero or by finding the difference.

In this lesson we've got Laura and Jacob who are gonna help us with our learning.

So when we measure the length of height of an object, it is more efficient to start at zero and that just means it's probably easier or better to start at zero.

I've got my toy car here and this is Jacob who says, "Oh I think that the length of the toy car is eight centimetres." Do you agree with Jacob? Has he started his measurement at zero? Ah, Laura is saying, "I disagree because you have not started at zero." And you see the toy car is not lined up with a zero on the ruler.

So he's not being very efficient.

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

And you can see Laura has now lined that toy car up with the zero and she can see then that the length of the toy car is seven centimetres because that is where the object ends and it has started at zero.

Now let's have a look.

Laura draws a line, "I think the length of the line is between 13 and 14 centimetres." Do you agree with Laura? Jacob doesn't.

Jacob disagrees because he can see that the line has not started at zero.

So Laura is not being efficient with her measuring.

There we go.

Jacob has lined the ruler up now with the line that has been drawn and we can see that if we start at zero, the length of the line is 14 centimetres.

So it's very efficient to start at zero on the ruler when you are measuring.

But do we have to start at zero when we're measuring? We know it's more efficient to start at zero, but do we have to? Well no we don't.

'Cause the length of an object is the difference between the numbers at the start and the end of the object.

So if I look at my toy car here, I've got my ruler lined up with the toy car but not from the zero I can see I'm put my objects at the five and it's finishing at the 12.

So to find the length of that object we need to find the difference the distance between how far apart those numbers are.

So my object is finishing at the 12 centimetres and it started at the five centimetres.

So if I subtract the five from the 12, it will tell us the length of the toy car.

So 12 centimetres subtract five centimetres in seven centimetres.

The difference between 12 and five is seven.

And that tells me then that the length of the toy car is seven centimetres.

So we do not have to start at zero.

It is more efficient to, but we do not have to start at zero.

But if we do not start at zero, then we need to find the difference.

So let's summarise what we've been talking about so far.

The length of the object is the difference between the numbers at the start and the end of the object.

But we can do this efficiently.

If we look at our second image here, if we line the car up with the zero on our ruler, we can be efficient because we only need to subtract zero 'cause that's where the car started.

Seven centimetres subtract zero centimetres, is seven centimetres.

It's easy to subtract zero, isn't it? But we don't have to line it up with zero.

But if we don't line it up with zero then we have to do find the difference with the numbers at the start and the end of the object.

So our first image here, we've got 12 centimetres, subtract five centimetres is seven centimetres.

Do you notice that whichever method we use, we still get the same length for the toy car.

We still get the seven centimetres.

So the length of the toy car is seven centimetres.

We can be efficient and line the car up with the zero on the ruler or we can find the difference and line the car up on the ruler wherever it suits us.

Now I wonder who you think is correct here.

Laura is saying I think the length of the line is 16 centimetres.

Oh yes, I can see why she's saying that.

Can you and Jacob is saying I think that the length of the line is 14 centimetres.

Hmm, I can see why he's saying that.

So maybe pause a video, find someone to talk to who is correct, Laura or Jacob? Hey, who do you think was correct? That's right, Jacob is correct.

Why is Jacob correct? Well Laura, she hasn't lined her ruler up with the start of the line.

So she is reading 16 where the line ends, but the line hasn't started at zero.

So she needs to find the difference and that's what Jacob has done.

Jacob has found the difference between the 16 and the two.

16 subtract two is 14.

So the length of the line is 14 centimetres.

Here we go.

Jacob is correct.

The line is not at zero.

So to find its length you need to find the difference between 16 centimetres and two centimetres.

16 subtract two is 14.

So 16 centimetres subtract two centimetres is 14 centimetres.

I think the length of line is 14 centimetres and Jacob was correct.

Can you see why Laura thought it was 16 centimetres though? Hmm, me too.

Because the line appears to end at 16 centimetres, doesn't it? It just because it didn't start at zero because it didn't start at zero we should have found that difference.

So I would like you to practise now your measuring skills.

I'd like you to find the length of these lines and then I want you to tell me what you notice about lines B and line C.

So take a look at each of the rulers and the lines and have a think.

Does it start at zero? In which case I can just read the number at the end of the line, but if it does not start at zero, I need to find that difference by subtracting the number where it started from the number where it ends.

And your second task today.

Jacob has broken his ruler.

Oh poor Jacob, what's he going to do? Can he still use his ruler to measure the length of the leaf do you think? What does he need to do? So I'd like you to answer whether or not you think he can use his ruler and how if you think it's possible, how is he going to use his ruler? Pause the video and when you are ready to check your answers, press play.

Here we go.

Are you ready to check your answers? So line A, the length of this line is 24 centimetres, line B, the length of this line is 12 centimetres.

Had to find the difference there, didn't we? Because it didn't start at zero.

Line C is 12 centimetres and line D is 27 centimetres.

What did you notice about lines B and C? That's right, lines B and C are the same length.

And did you realise that in question two Jacob could still use his ruler, his broken ruler, but this time he has to think about the difference between the numbers at the start and the end of the leaf.

So he could have put his ruler near to the leaf.

And for around my example here, I've lined my leaf up with the five and the 11.

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

11 centimetres subtract five centimetres is six centimetres, so the leaf is six centimetres long.

So yes, Jacob could still measure the leaf with a broken ruler.

He just needs to find the difference because he could not line the leaf up with the zero on his broken ruler.

Okay, if we think about the next part of our learning, we're gonna move on and thinking about estimating and having a think about is it better to measure in metres or is it better to measure in centimetres and how we might be able to work that out.

So centimetres are used to measure the length or height of objects that are smaller than a metre, like the length of a book.

Maybe you've got a book near you now that you could have a look at that is smaller than one metre.

So we would use centimetres.

Metres are used to measure the length or heights of objects that are greater than a metre like the length of a room that would be measured in metres.

You wouldn't want to measure the room in centimetres.

That would take a long time.

And you can decide whether to measure in metres or centimetres by estimating the length or the height of the object first.

So that means we have to have a think about roughly what we think the measurement, the length of the height of the object might be and that will tell us whether to measure in metres or centimetres.

So if an object is long or tall we usually measure in metres.

If an object is short, we usually measure in centimetres, and centimetres are used to measure the length or height of smaller objects.

I wonder if you can think of some objects that we might measure in centimetres.

These are some that I thought of.

The height of a bottle of water.

I would measure that in centimetres the length of a paper aeroplane we would measure in centimetres or maybe the height of an ice cube.

We would measure that in centimetres.

And what might we measure in metres? I wonder metres are used to measure the length or height of longer or taller objects.

Can you think of any objects that you might measure with metres? Here are some that I've thought of the length of a field.

Can you see how that is bigger than the length of my book that we had before? So my book we would measure in centimetres, but the length of a field that is longer so we need to measure in metres.

I also thought about the height of a giraffe.

That's a long or a tall, I should say tall animal.

So we would need to measure that in metres.

What about the height of a mountain? That's definitely tall.

So we would definitely need to measure in metres the height of a mountain.

If you are not quite sure to measure in metres or centimetres.

We have got some everyday objects that can help us to estimate.

Hmm, I wonder if we can help Laura here.

She wonders what objects we know that are about one centimetre.

Do you know any objects that are about one centimetre? Hmm, I think Jacob knows.

He knows that your thumb is about one centimetre wide.

Okay, so have a look at your thumb and your thumbnail that is about one centimetre wide estimate.

So it's roughly one centimetre wide.

So we can use that to help us when we estimate something.

So I wonder if we can think of any objects that are about one metre and we can help Laura answer her questions.

Do you know any objects that are about one metre? Hmm, I think Jacob can help us.

Jacob knows that the width of a door is about one metre.

I wonder if you've got a door that you can see from where you are now.

Have a look at the door, the width.

So that's the bit that goes across.

That is about one metre.

So we know that we've got a thumbnail is about one centimetre and the width of a door.

If I show you here, that is also one metre.

So we can use the width of a fingernail at one centimetre and the width of a door at one metre to help us estimate and to help us work out if we should be measuring in centimetres or if we should be measuring in metres.

Okay, let's see what you have learned so far.

I wonder if you can tell me which unit would you use to measure the length of a pencil? So think is it gonna be centimetres or is it gonna be metres? The length of a pencil, is it metres or centimetres? Or maybe you are not sure, press pause and tell the person next to you or go and find someone if you can and tell them what you would use as a unit to measure the length of a pencil.

Okay, what did you decide? That's right.

Centimetres would be used to measure the length of a pencil because it's smaller than one metre that we would use centimetres.

What about the height of a tree? What unit would you use to measure the height of a tree? Would you measure in metres or centimetres? Pause the video and tell someone what unit you would use to measure the height of the tree.

Okay, what did you decide? That's right metres.

Metres would be used to measure the height of a tree 'cause it's taller than one metre.

So centimetres are too small to measure the height of a tree.

So we would use metres.

Okay, so now I'm gonna get you to have a go and practise what we've been learning about estimating and helping us know if that is better to measure in metres or centimetres.

So I want you to find two things you would measure in centimetres and two things that you think you would measure in metres.

Go and have a look around the area where you are now.

Explain why you would measure them with your chosen unit.

So I would measure this in centimetres because.

And I would measure this in metres because.

Try and think about what we've been learning about measuring shorter things in centimetres or taller or longer things in metres.

And for your second task today, I would like you to estimate the lengths and heights of the objects you chose in that first task.

So the objects that you chose for your centimetres, how many centimetres do you think that object is? And the same with your metres.

How many metres do you estimate your objects is? And then estimate is just your best.

Thinking about the value that you think would be closest to the real value, press pause and then when you are ready to check your answers to task one and two, press play.

Okay, these are some objects that you might have found.

So I found some glasses to measure in centimetres because they are short.

I also found a plant that I would measure the height of because it's short.

And then I found a car and a house that I would measure in metres because the car is long and the house is tall.

For the second task, I estimated that the length of the glasses would be about 15 of my thumbnails.

So 15 of those.

And I estimated the height of the plant to be 30 centimetres and then estimated the length of the car to be four metres and the height of the house to be eight metres.

So those are the estimates for the objects that I found.

Okay, brilliant learning today everybody.

So if we just summarise what we have been thinking about, we've got the length of the objects is the difference between the numbers on the ruler at the start and the end of the object.

So here my toy car is lined up with a nine and the two.

So we found a difference.

Nine subtract two is seven.

So the car is seven centimetres long.

But we decided it was actually more efficient if we line our object up with the zero.

If we line the object up with zero, it's easy to do to find the difference 'cause we're subtracting zero.

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

And when the height, length, or height of an objects is measured, we can give the me the measurement in metres and in centimetres.

And estimating helps us decide to decide if it's better to measure in centimetres or metres.

So thank you for your learning today.

I hope you have deepened your understanding of measures in particular of when we can use metres and centimetres and about how you can find the length or the height of an object.