Lesson video

Hello, I'm Mr. Tilstone.

Today I get the opportunity to work with you on a lesson about negative numbers.

So if you are ready, let's begin.

The outcome of today's lesson is I can read and write negative numbers.

We've got two keywords, so I'll say it and you say it back.

So my turn, your turn.

Ready? So my turn, numeral, your turn.

My turn, negative number, your turn.

Let's find out what those words mean.

So a numeral is a symbol or name that stands for a number.

So some examples are 49 and six.

Numbers less than zero can be described as negative, and you may have encountered that knowledge recently.

Let's begin.

Our lesson has got two cycles.

The first is writing negative numbers and the second is reading and writing temperatures.

So the first one's writing negative numbers, let's start that.

In this lesson you're going to meet quite a few different characters.

So we've got Laura, Aisha, Andeep, Izzy, and Jacob, all along to give us a little hand.

Certain values can be thought of as being above zero or below zero.

So here we've got a house and we've got a ground floor on the house that we could call zero.

Now we've got a floor above zero, above the ground floor, that we could call the first floor and we've got one above that, what do you think that would be called? The second floor.

And then we've got a floor below that which we could call a basement.

What else could we call it? Hmm, we could call it a first basement.

So these values can also be thought of as either being positive or negative.

So let's look again.

So we've got a zero again, or ground floor.

So everything above the ground floor is positive, so the floor above that would also be positive.

And everything below zero, below the ground floor, could be thought of as being negative.

So everything above zero is positive and everything below zero is negative.

And zero is special because it's neither positive nor negative.

Numeral, so that keyword in action, can be used to show their position from zero.

So let's look again.

So once again we've got zero, the ground floor.

What number, what numeral would go above that? Well, we could say +1, because it's positive.

Above that we could say +2 or positive 2.

Below that we could say, what do you think? Hmm.

We could say -1, and that's the symbol that we use for -1.

Positive values are not typically denoted with the plus sign, the positive sign.

So we don't tend to use that, we just presume they are unless we see otherwise.

However negative values do have that special symbol.

And this is read as -1.

You might also hear minus one, and that's correct as well, but today we're going to be using the language -1.

Let's change the context.

So some hotels and blocks of flats have floors on, above and below the ground.

You might be lucky enough to have stayed in a hotel that's got floors below the ground before.

I know now I have.

So we've got zero, or the ground floor, then we've got the first floor, second floor, third floor, fourth floor, fifth floor.

Remember these are all positive values.

Everything above the ground floor is positive.

Everything below the ground floor, however, is negative.

So you can see some floors below that zero mark, below the ground floor.

So we've got that first basement, second basement, and third basement.

And they're negative values, they're below zero.

We could use numerals.

So we've got 0, one, two, three, four, and five for the positive floors.

We've also got some negative floors.

Now what could we call those? What numerals should we use to call those? What would be the first one, I wonder, below zero, that we work on in the first basement? The negative values are represented by writing or saying the negative sign first and then the digit.

So -1, what do you think is gonna come next? <v ->2.

</v> And finally, -3.

Negative values can often be seen on lift buttons.

So here we go, you might see if you've got into a lift before, you might have seen a little panel looking something like that, and you can see there's negative values on there.

Let's do a check.

Let's see if you've understood the lesson so far.

Laura has labelled this hotel image with positive and negative numbers.

Laura's made a mistake, explain her mistake to a partner.

So have a look at that.

So it's going five, four, three, two, one, 0, -3, -2, -1.

Hmm, something doesn't seem right about that.

Have a chat to your friend, pause the video, we'll do some feedback shortly.

Let's have a look at what Laura did wrong then.

Now if you remember the first floor below zero, below the ground floor, we did call first basement, we could also call it -1.

So the first floor below zero is -1.

Let's change our context.

So we've got a sea and we've got land and we've got a sea level and things above and below sea level.

We've got a number as well to use to represent the sea level, which is zero.

Places above sea level, that is above zero, have a positive elevation, so everything above that is positive.

And on this particular image it goes up to 100 metres.

So you can see the top of those trees is 100 metres high above sea level.

Places below sea level, that is below zero, have a negative elevation and negative value.

Now you can see this goes down to -275 metres.

And remember zero is neither positive nor negative.

So we've got something of a number line now, going alongside this image.

It's not got intervals on, it's not got labels on, but there are values in between zero and 100 and between zero and -275.

Okay, so a little check for understanding.

Write the number of this floor using the negative symbol.

Pause the video, have a go.

How did you get on with that? What do you think that was? That was -3.

So big well done if you got that, you are definitely on track.

Do you think you might be ready for some independent practise? I think you are.

So for task A, Laura uses the lift to go to the second floor below the grass, now think where the ground floor is, she goes to the second floor below the ground, shade in the floor the lift takes her to and use a negative symbol to write the number of the floor.

And then the next task is give a possible value to each of the blank boxes.

So we can see we've got three blank boxes, what could their values possibly be? Use your estimation skills and use what you know about negative numbers.

Okay, pause the video, very best of luck, and we'll see you shortly for some answers.

Okay, welcome back, how did you get on? Find it easy, hard, somewhere in the middle? Let's find out.

Okay, so Laura uses the lift to go to the second floor below the ground, so the floor that you need to shade in is that one in purple on the screen and that is -2.

And that is how we write -2.

Well done if you got that.

And then a possible value for each of the blank boxes.

Well you might have slightly different numbers to this, but I noticed the middle one was about halfway between zero and -200, so I put -100.

And then I noticed the one just above that, was halfway between those, and I know that halfway between zero and 100 is 50, so halfway between zero and -100, -50.

And then the final one that's halfway between -100 and -200.

And I know that halfway between 100 and 200 is 150.

So I use that knowledge to determine that it's probably -150.

You might have some small variations on the numbers that you put, but numbers something like that.

Well done if you've got that.

Cycle two, are you ready? Let's give it a go.

So this is reading and writing temperatures.

Have you ever noticed that thermometers have got this symbol on them? It's short for degrees Celsius and it is written and read straight after the number.

This tells you how hot or cold something is.

Often people shorten it when saying the temperature.

So they might say something like eight degrees rather than eight degrees Celsius.

They're both acceptable.

Temperatures warmer than zero degrees are positive, and there's no need to say positive 10 or use the positive symbol, we just assume.

Temperatures colder than zero degrees are negative.

We read this one, this example here where the arrow is, as -10 degrees.

And where the arrow is pointing now, we could read as -40 degrees.

Sometimes people say minus 10 and minus 40.

The scales on thermometers do not always go up and down in ones.

The ones we've looked at so far have, but that's not always the case and it's not the case with this example here.

Here's part of a thermometer, what is the value of each of those intervals? Hmm, it's not ones.

So we can see there are five intervals between zero and 10.

10 divided by five equals two.

So therefore, each interval is worth two degrees celsius.

So it's not going up in ones, in this case, it's going up in twos.

Sometimes the temperatures are easier to read if they are exactly in line with a marked interval.

So let's have a look at this.

So we've got another thermometer that's going up and down in twos.

So here we've got -10 degrees, so it's exactly in line with that marked interval.

That interval's got a number next to it and it's -10, so fairly easy.

And the same with this one.

That's -30 degrees, it's exactly in line with -30.

But that's not always the case, so look at this example here, it is not in line with a -10 and it's not in line with a -20, it's in line with something unmarked between them.

So this temperature is in between two multiples of 10, so -10 and -20.

Each interval's worth two degrees Celsius.

We've worked that one out already.

So it goes -10, -12, -14.

So the temperature is -14 degrees celsius.

Let's check to see if you've understood that.

So what temperature is this thermometer showing? And you've got three options here.

Is it showing -18 degrees? Is it showing -19 degrees? Or is it showing -21 degrees? And they're all quite plausible options there, but only one of them is right.

So pause the video and see if you can work that out.

Did you get it? <v ->18 degrees Celsius.

</v> Are you ready for some independent practise? I think so.

So task one, write down the temperature shown on each thermometer in degrees Celsius.

So you've got four different temperatures, they look very different, the thermometers look different to each other, they go up and down in different intervals.

See if you can work out the temperature please.

And then question two, who is correct? Explain why the other three children might have made those mistakes.

So have a look at the temperature here.

Aisha thinks the temperature is -21 degrees Celsius.

Is that right or wrong? If you think that's wrong, why? Why might she have thought that? Andeep thinks the temperature is -14 degrees.

Is that right? Why might he have thought that? Izzy thinks the temperature is -18 degrees Celsius.

Is that right? And Jacob thinks the temperature is -22 degrees Celsius.

Only one of those is right.

So what you're going to do is find out who's right and explain why the other three children thought it was those temperatures.

Pause the video, good luck, and I'll see you very soon for some feedback and some answers.

How did you get on with that? Let's have a look.

So for number one, the temperatures were as follows.

So the first one showed 12 degrees Celsius.

Now that thermometer went up and down in ones, the intervals are worth one.

We've got some marked intervals on there, they're multiples of 10, but we could work out by counting in ones that the next one was 12 degrees Celsius.

And for B we've got -35 degrees Celsius.

Now this one was going up and down in twos, and the temperature was in between the two intervals.

So it was in between -34 and -36, so it's -35 degrees.

The next one again going up and down in ones.

So that was -7 degrees Celsius.

And the final one, going up and down in twos, that is 28 degrees Celsius.

So for task two, who's correct? Explain why the other three children might have made those mistakes.

Well, Aisha thinks the temperature's -21 degrees Celsius.

It isn't, but I can see why she thought that.

She made two mistakes.

The first one, she hasn't noticed that the value is in between -10 and -20, so therefore it couldn't possibly be -21.

And she hasn't realised that the scale goes up and down in twos.

She was thinking it was going up and down in ones.

So she made a couple of mistakes there.

But good try.

Andeep thinks the temperature's -14 degrees Celsius.

Well, he's not realised that the scale goes up and down in twos, he did know it was in between -10 and -20, but he thought it was going up and down in one.

Izzy thinks the temperature is -18 degrees and indeed it is.

It's in between -10 and -20 and it's going up and down in twos.

So therefore it's -18 degrees Celsius.

So well done Izzy.

And then Jacob thinks the temperature is -22 degrees.

That's not right.

He has realised the scale's going up and down in twos, so that's good he noticed something, but he has not noticed that the value is in between <v ->10 and -20.

</v> We've come to the end of the lesson.

Today's lesson has been reading and writing negative numbers.

So values below or less than zero are referred to as negative numbers.

They look like this and they're spoken like this.

<v ->1, -2, -3.

</v> Occasionally be spoken like this, minus one, minus two, minus three.

And that's correct, but in today's lesson, we've been using the language, negative.

Very well done on today's lesson, you've done amazingly well and hopefully I get the chance to work with you again in the near future.

Until then, take care and goodbye.