91�ȱ�

MINNA KANE:Often computers show us a world, whether it's an imaginary world in a fantastic console game, or the real world in a highly accurate racing simulator. So how do we create the virtual world? Well we have to create a computer program that describes how everything works.

MINNA KANE:I'm here with the pupils from The Ilsleys Primary School, and we're going to see if we can create a virtual car that can steer itself around a track. But first of all we need to get a track, so let's go guys!

MINNA KANE:'To draw our track, and to do our programming, we’re using Scratch, a free piece of coding software. All the commands you might need are laid out on the left-hand side. You then drag commands into the middle to write your program. On the right of the screen is the stage, and this is where we are going to put our car and our track.'

MINNA KANE:Great, so you've drawn your track. Now what are you doing?

STUDENT #1:We have to get a new sprite, so you have to go onto the file, and go to home, and choose one of these.

MINNA KANE:Okay.

STUDENT #1:And then if you right-click, you can resize it.

MINNA KANE:'This sprite represents the car. Once we've loaded our sprite, we're going to need a way of steering it round our track. We can tell where the track is, because it's a different colour to the background. Before we write our code, we're painting different colours on the left and right front corners of the car. We're going to use these colours in our program to try and stay on the track. We're writing a simple program using "if" conditions, and the colours on the front of the car. If the colour on the left side of the car touches the background colour, then the program knows that the car is heading off the track, onto the background. It's driving too far left, so we need to turn the car to steer it back on to the track. 'If the colour on the right of the car touches the background, 'then we need to turn the other way, so we stay on the track.'

MINNA KANE:Oh that looks awesome, but what's the code? What are you doing?

STUDENT # 2:Well what you have to do is put these colours in, this is the background.

MINNA KANE:Oh okay.

STUDENT #2:And then this is my left side of the car. So if it goes close to here, it should turn 15 degrees that way.

MINNA KANE:Okay so the lights are acting like sensors really, which help navigate the car round.

MINNA KANE:'To get all the way round the track, we repeat these commands over and over again. So we've placed them inside a forever loop. In this program, we're using a variable to store the speed of our car. We can change how fast the car moves, by changing the value of our variable.'

MINNA KANE:What do we do now?

STUDENT #2:Well we need to put speed in, and set the speed to…

MINNA KANE:A value.

STUDENT #2:10.

MINNA KANE:10, okay.

STUDENT #2:And then when I press the flag, it should go round.

MINNA KANE:Ah, oh yeah. Oh.

MINNA KANE:'Whoops, looks like this car's having trouble staying on the track.'

MINNA KANE:How come it's going off?

STUDENT #2:I'm not sure.

MINNA KANE:Shall we try a slower speed, so we've just got a bit more time to see it?

STUDENT #2:So let's try 5.

MINNA KANE:Yeah.

MINNA KANE:Cool. Oh it can handle it a bit better now.

STUDENT #2:Yeah.

MINNA KANE:Okay that's great.

MINNA KANE:Wow that's crazy, what's happened to your car?

STUDENT #3:I don't know.

MINNA KANE:You don't know? Why don't you try changing it to a lower speed, then it may work.

MINNA KANE:Okay guys, your times up. I want to know who has the best speed. So what did you get?

STUDENT #4:Seven.

MINNA KANE:Seven, anyone got higher than seven?

STUDENT #5:Me.

MINNA KANE:You? What did you get then?

STUDENT #5:I got 12.

MINNA KANE:12, let's see.

MINNA KANE:Oh wow, you did. That's fantastic. But you do have a rather simple oval track. Do you reckon if it was a bit complicated, with more twists and turns it would still be able to go 12?

STUDENT #5Yeah.

MINNA KANE:Yeah? I think you should give it a go.

MINNA KANE:Everybody's computer model was pretty similar, but by changing a parameter such as the speed, we're able to change how things work.

MINNA KANE:'I wonder if there are any other changes we could make to our program, to make the car behave differently. Why doesn't our program work at high speeds? And is there a way of making it work better? Perhaps you could try experimenting yourself.'