Learning Goals 3 min
By the end of this lesson you will be able to:
- Explain that one step is one pixel on the Scratch Stage.
- Predict where the cat lands after a
move (100) stepsblock runs. - Build one big move and many small moves, and show that they end in the same place.
Warm-Up 7 min
New arc, new project. Start a fresh Scratch project and choose the Garden Rock backdrop — this garden is where the cat will live for the next eight lessons. You already know move (10) steps. Today you find out what that 10 actually measures.
Quick-fire puzzle
Wei Jie built this stack and clicked the flag once. The cat started at x = 0. Where did it end up?
when flag clicked
move (60) steps
move (60) steps
move (60) steps
move (60) steps
Reveal the answer
The cat ended at x = 240 — hard against the right edge. Each move adds 60, and 4 × 60 = 240. The cat began at the centre, and the edge is 240 away.
Notice that four separate moves looked like one jump. Scratch runs blocks far too quickly for your eye to catch the stops in between.
New Concept — what a “step” really is 15 min
A step in Scratch is not a footstep. It is one tiny dot of light on the screen — a pixel. So move (10) steps slides the cat ten dots forward, which is a much smaller distance than the word “step” suggests.
The block we are studying today
| Block | Category | What it does |
|---|---|---|
move (10) steps | Motion | Slides the sprite forward by that many pixels, in whatever direction it faces. |
How big is one step?
The Stage is 480 pixels wide and 360 tall. That gives you a scale to think in:
- 1 step — a nudge you can barely see.
- 10 steps — a small slide, easy to spot.
- 240 steps — half the Stage: centre to one edge.
- 480 steps — the whole Stage: edge to edge.
Changing the number
Click the white oval inside the move block and type whatever you like — positive, negative, even zero.
move (50) steps— slide 50 pixels forward.move (-50) steps— slide 50 pixels backward. A minus sign reverses the move without turning the cat round.move (0) steps— do nothing at all. Occasionally useful, mostly just funny.
One big move versus many small ones
There are two ways to get from the centre to the right edge:
- One big move —
move (240) steps. The cat arrives instantly. - Twenty-four small ones —
move (10) steps, over and over. The cat still arrives instantly, because Scratch runs them all before the screen redraws.
To your eye they are identical. The difference only appears once you put wait (1) seconds between the small moves — then the cat walks instead of teleporting. You met that trick in Lesson 4, and it becomes the whole point in Lesson 18.
Distance is just addition
However many move blocks you stack, the cat’s finishing position is the starting x plus the sum of every number. That is the only sum you need today, and it works every time.
Why it matters
Every walking sprite, every animated game, every smooth slide is built from this one block plus something to slow it down. Master the block now, and the rest of the arc is decoration.
Worked Example — Faiz’s cat crosses the garden 15 min
We will reach the same spot in three different ways, and prove that only the total matters.
Step 1 — Put the cat on its mark
Select the cat. In Sprite Properties set x = -200, y = 0, Direction = 90. The cat sits at the left of the garden, facing right.
Step 2 — Version A: one big move
Drag in when flag clicked, then move (10) steps. Click the oval, type 400, press Enter.
when flag clicked
move (400) steps
Click the flag. The cat crosses the garden in an instant. Check the x box: it reads 200.
Step 3 — Reset and try Version B
Set x back to -200. Delete the move block by dragging it onto the Blocks Panel. Now snap in eight move (50) steps blocks.
when flag clicked
move (50) steps
move (50) steps
move (50) steps
move (50) steps
move (50) steps
move (50) steps
move (50) steps
move (50) steps
Click the flag. The cat lands on 200 again, and it looked identical. Your eye cannot tell eight moves from one.
Step 4 — Version C: uneven strides
Reset to -200 once more and try a lopsided version, where one block does most of the work.
when flag clicked
move (50) steps
move (50) steps
move (50) steps
move (200) steps
move (50) steps
Step 5 — Prove it with the x box
All three versions end with x reading 200. Different block counts, different numbers, one answer — because the cat’s finishing spot is simply the start plus the total.
What changed: you can now predict where the cat will stop before you click. That is the difference between guessing at numbers and designing a movement.
The full assembled stack (your reference)
when flag clicked
move (400) steps
Try It Yourself — three small builds 12 min
Goal: Send the cat backwards without turning it round. Reset x to 0, build the stack, and click the flag.
when flag clicked
move (-100) steps
Think: the minus sign reverses the movement, not the sprite. Check the x box — it should read -100, and the cat should still be facing right.
Goal: Track the cat through four equal strides. Reset x to -200, build the stack, and work out where each block leaves it before you click.
when flag clicked
move (100) steps
move (100) steps
move (100) steps
move (100) steps
Think: the cat passes through −100, 0, 100 and 200. On screen it looks like one zoom, but the arithmetic is four separate jumps.
Mini-mission: hit the flowerbed. Aisyah has marked a spot in the garden at x = 90. Start the cat at x = -150 and land it exactly on that spot — using exactly three move blocks, and no two of them the same number.
It works if: after one flag click the x box reads exactly 90, your stack holds exactly three move blocks, and all three numbers are different. Use no more than 8 blocks in total.
Think: how far is it from −150 to 90? Find that number first. Everything after it is just choosing three numbers that add up to it.
Mini-Challenge — home in two clicks 5 min
“Send the cat home”
Start the cat at the left of the garden, at x = -200. Build one script so that clicking the green flag twice — and only twice — leaves the cat dead centre.
It works if:
- The cat starts at x =
-200. - Two clicks of the green flag — no more, no fewer — leave it at x =
0. - You changed nothing between the two clicks.
Reveal one valid solution (teacher)
The whole journey is 200 pixels, and the same script runs twice, so each run must cover half of it.
when flag clicked
move (100) steps
Click 1 takes the cat from −200 to −100; click 2 takes it from −100 to 0. Pupils often try 200 in the block and overshoot to +200 on the second click — a good moment to talk about what “runs again” means.
Recap 2 min
One step is one pixel. The Stage is 480 wide and 360 tall, so 240 steps carries you from the centre to either edge. Negative numbers walk backwards without turning the sprite. And wherever the cat ends up is simply its starting x plus the total of every move block — many small moves and one big move look exactly the same until you add a pause.
- Step
- One pixel of distance on the Stage.
move (10) stepsslides the sprite ten pixels forward. - Pixel
- One tiny dot on the screen. The Stage is 480 pixels wide and 360 tall.
- Negative move
- A move block holding a minus number. The sprite walks backwards, still facing the same way.
- Forward
- Whichever way the sprite is facing. Direction 90 means right, which is why forward usually looks like right.
Homework 1 min
The 360-step trip. Start the cat at x = -180 and land it on x = 180 with a single flag click — using at least three move blocks in one stack.
- Set Sprite Properties to x =
-180, y =0, Direction =90. - Build a stack starting with
when flag clickedand three or moremove (10) stepsblocks whose numbers total 360. - Click the flag once, then read the x box. It should say
180. - Screenshot your Script Area and the Stage after the click.
Bring back next class:
- Both screenshots.
- Your list of move numbers written out, with the sum shown, proving they total 360.
Heads up for next class: SCR-L01-08 adds two new Motion blocks — turning clockwise and anti-clockwise. The cat learns to change where “forward” points.