Week 2 (2nd June) Activities

Week 2 (2nd June)

Figure 1: Simple number line starting from 0

This week we reviewed the basics of the number line.  Most students at year 3 level are used to the number line starting at zero and going to infinity, as shown in Figure 1.

Figure 2: number line going from minus infinity to positive infinity

However in practice the number line can extend just as far to the left, and to show this we use negative numbers, as shown in Figure 2.  

Figure 3: x-axis numberline in Scratch going from -240 to +240, with 0 in the middle

We can use this number line concept to move objects around the screen in Scratch.  but infinity is a pretty big number and our screen has only 240 spots (or pixels) to the right of zero and 240 pixels to the left of zero.  We call this the x-axis and this is shown in Figure 3.

Figure 4: x and y axis combined 

Now if we turn this number line so that it points up and down, with positive numbers going up we still have a number line.  We call this the y-axis and these numbers in Scratch have 180 pixels above zero and 180 pixels below zero.  We can combine both x-axis and y-axis as shown in Figure 4.  In mathematics, this is called the xy-Cartesian axis.  To put an object at the top right location, you would set the x=240 and y=180, and we right this as (240,180) or (x,y) where x comes first, then y.

To help move objects around the screen in Scratch, you can use the xy-grid backdrop in Sratch, which is shown in Figure 6.  This really helps to figure out the (x,y) location on the screen where you want your sprite to go.

Figure 5: xy grid backdrop available in Scrtach

In Week 2, students should practice using the "GLIDE" command in scratch to move a Sprite around the screen, going from each corner to each other corner by specifying the (x,y) locations to glide to.