Lesson video

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Hi, everyone.

How are you doing today? Today in maths we're going to be measuring length in centimetres.

For today's lesson, you will need small objects of different size.

For example, a pen, a book, some pasta, a piece of paper.

But please make sure you ask your parent or carer before touching these items. You will also need a pencil and some paper, and also a ruler.

Pause the video now to get this if you have not got it already.

A metre is a standard unit for measuring length.

And we use metres for larger items when we're measuring.

A centimetre is a standard unit for measuring length, but we use centimetres for smaller items. So metre larger, centimetre smaller.

Can you say the word centimetre? Centimetre.

Now centimetre is our star word today, and that's going to come up a lot in our lesson, and you will be using that word a lot as well.

There are 100 centimetres in one metre.

There are 100 centimetres in one metre.

And today we're going to be measuring with a ruler.

So I have drawn a line, as you can see here, and to measure the length of that line, the first thing I need to do is line up the zero on my ruler, right at the beginning of the line.

Now, I don't start from the edge of the ruler.

That is not correct.

You start on the number zero.

And you need to make sure that you line your ruler up the whole way along, so it's nice and straight.

If it's not straight, you will not get an accurate answer.

You then look at where the line ends, you go down carefully to read what number is written there.

So I can see that my line ends at the number 20.

So I can see that my line is 20 centimetres.

Now instead of writing centimetres every time, you can just write cm.

Cm stands for centimetres.

So I know that this length, the length of this line is 20 centimetres, because the end of my line says 20.

Okay, here is a different question for you.

So I have my line, my same line and my same ruler.

But why is this measured incorrectly? Could you pause the video, and explain to me why this has not why been measured correctly.

Okay, so two reasons.

The first reason is the ruler is not right against the line.

Do you see this big gap here? There should be no gap between what you're measuring and the ruler.

So that is the first mistake.

The second mistake is that the beginning of the line is not on the number zero.

It's just kind of in between zero and one.

So that's not going to give me and very accurate measurements.

So two mistakes here, one, the ruler is not against the line, and two, the line is not starting at zero.

Okay, here is a different one.

Could you pause the video and tell me why this has not been measured correctly? Did you manage to spot my mistake? Now this has not been measured correctly, because although my line is right against the ruler, and it's nice and straight, I have not started at the number zero.

I've started at the beginning of the ruler, but I know that's not where I start, my line needs to start on the zero.

So this is incorrect, because I have not started measuring from the zero.

Okay, and finally, can you tell me why this line has not been measured correctly? Pause the video and tell me now.

So this has not been measured correctly, because again, although it is straight and the ruler is against the line, I have started measuring from the wrong end, I've started measuring from the number 30 at the end of the ruler rather than starting at the zero, so this does not give me a correct reading.

So this is incorrect because I have started measuring from the wrong end, I have started measuring from the 30, and not the zero.

So for your independent task, you are going to be measuring the length of your objects in centimetres.

You're going to write the objects on one side of your table and then you're going to tell me the measurements on the other side.

Remember you don't need to write the word cm, you can just write the letters cm.

And here are some example of my answers.

If you can, ask a parent or carer just to check that yours are correct.

Well done for today's learning.