Lesson video

Hi everyone, Miss Miles here.

Today we're going to be doing some math together.

Before we start, a did you know fact.

Today's fact is, did you know that up until the 16th century, math equations were all written in words? Very time consuming.

Okay, back to the Maths.

Before we start, please make sure that you have done the pre lesson quiz.

For today's lesson, you will need a pencil, a piece of paper, and a clear workspace.

In today's lesson, we are going to be illustrating and naming parts of a circle.

And when you're ready, let's get started.

Onscreen now, are a few different shapes.

I would like you to pause your video, and have a think about what you can say about those shapes.

Pause your video there.

Okay, I can say that these shapes are not polygons, and I know that because none of them have three or more straight sides.

The only shape that does have a straight side, is my semi circle.

I also have three circles and an oval one there.

Now, if I was describing those shapes, I would say that they had one curve side.

But, if that's how I would describe them, how could I differentiate between an oval and a circle? Well, let me show you.

I have drawn some images here after one circle and one oval.

Now, I'll hold it up so that you can see.

So here is my circle.

I've popped a centre point on there.

And I have drawn some lines, to show that from the centre point of a circle to any point around the curved side, it is the same distance apart.

However, on my oval, popped a centre point on there as well.

If I look to the curved side on an oval, I can see that this side here, this line I've drawn up, is actually further away than here.

So on a circle, the distance from the centre point to the curve side is an equal distance at any point.

And on an oval, that is not the case.

So that's how we would differentiate between a circle and an oval.

Now, we're going to have a closer look at circles.

Onscreen now is a big picture of a circle, with three different coloured lines.

The orange line that goes all the way around the edge, is the circumference.

Can you say that? Circumference, all the way around the edge.

Now the blue line, is the diameter.

Can you say diameter? That goes from one side of the circle, to the other through a centre point.

And then last one, the green line is radius.

Can you say that for me? The radius goes from the centre point to any part at any point around the circumference.

Now, I've made a little video to show you that a little bit clearer.

So, here we go.

Okay, so here's my circle, going to start by showing you the circumference, the distance all the way around the edge.

Now the diameter that goes from one side to the other through the centre point, and here is my radius from the centre point to the circumference.

Now, I'm going to measure the diameter using the ruler.

So I placed my ruler onto my circle where my diameter is, with zero at one end.

And then I really carefully measure it to see that my diameter is 21 centimetres.

Now, I'm going to measure the radius.

The radius.

Again, we start with our ruler at the beginning at the centre point.

And then we measure out to the circumference.

And I can see, if I look really closely that my radius is 10 1/2 centimetres.

Now the radius is actually half the diameter.

So, my diameter was 21, and my radius was 10 1/2.

10 1/2 is half of 21.

Now, now you know that, let's apply that knowledge remembering that the radius is half the diameter.

So the diameter is double the radius.

Onscreen now, there are some statements that you need to complete.

The first one says, if the radius is five centimetres, the diameter is something.

The second one, if the diameter is 12 centimetres, the radius is something, for that one.

If the radius is 37 centimetres, the diameter is something.

And the last one, if the diameter is 70 kilometres, the radius is something.

Pause your video there, and have a go at filling in those statements for me.

Okay, let's have a look at our answers together now.

So the first one, if the radius is five centimetres, the diameter is 10 centimetres.

We know that because the diameter is double the radius and double five is 10, so 10 centimetres.

Our second one, if the diameter is 12 metres, the radius is six metres.

Now I know that the radius is half of the diameter, so half of 12 is six, so the answer is six metres.

Okay, let's have a look at number three.

If the radius is 37 centimetres, the diameter is 74 centimetres.

Again, I know that the diameter is double what the radius is.

So double 37 is 74.

And the last one, if the diameter is 70 kilometres, the radius Is 35 kilometres.

The radius is half of the diameter, and half of 70 is 35.

How did you get on? if you need to make any corrections, please do that now.

Okay, we're going to look now at finding the circumference of objects around our house.

And I'm going to show you how I did that with a mug from my kitchen.

Okay, so I'm going to use string and a ruler for this.

So I start, I'll hold my string at a point around on my mug, and then I measure my string all the way around to where I first put my finger on, and then when it meets a pinch it really, really tights, I let go.

And then I use that piece of string that went round my mug, and I measure it against the ruler, and I can see that the circumference of my mug, is 27 centimetres.

Now it's your turn.

Independent task, find three objects in your house which have a circular face, just like my mug did.

Use a piece of string or a tape measure and a ruler to find the radius, diameter and circumference of these circles.

So just like I did with my mug, you need to get some household things, some string or a tape measure, or anything you can find, and a ruler, and have a go at finding the circumference of the shapes of those objects.

Or you could also find the diameter and radius as well.

Pause your video there and have a go at that.

Well done for completing today's lesson.

Please don't forget the end of lesson quiz! And I'll see you very soon.