If on Edge, Bounce — Scratch L1

WHAT IT SHOULD LOOK LIKE

Where this arc is heading: everything you have learned becomes one showpiece — the cat crossing the garden.

where the arc is heading

step 1 of 2

the sprites move as they would on the real Stage

Learning Goals 3 min

By the end of this lesson you will be able to:

Explain in your own words what if on edge, bounce checks before it does anything.
Place the block after a move so the cat turns round instead of getting pinned to the edge.
Predict what the Direction box will read after a bounce off any of the four edges.

Warm-Up 7 min

Your cat can go anywhere in the garden and face any way. But there is one thing it still handles badly, and you have probably already seen it happen.

WHAT IT SHOULD LOOK LIKE

Where we are now. Reach the edge and the cat simply stops there, still facing outward. Click again and nothing happens at all.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Quick-fire puzzle

Daniel built this script and clicked the flag three times. The cat began at the centre. What happens on the third click?


when flag clicked
move (200) steps

Two blocks, three clicks, one very determined cat.

Reveal the answer

Click 1 takes the cat from 0 to 200. Click 2 tries for 400, but the Stage stops it at 240. Click 3 does nothing at all — the cat is already against the edge and there is nowhere further to go.

The cat is not broken. It is simply still facing right, with no right left. Today’s block notices that situation and turns it round.

New Concept — bouncing off the edge 15 min

Think of a ball rolling across a room. When it meets the wall it does not stop dead or pass through — it comes back. if on edge, bounce gives your sprite that same behaviour in one block.

Blocks reference

Block	Category	What it does
`if on edge, bounce`	Motion	Checks whether the sprite is touching an edge. If it is, flips the heading round and nudges it back inside. If it is not, does nothing whatsoever.

It asks a question first

This is the first block you have met that decides something. Every block so far has simply done as it was told. This one looks at the Stage first and only acts if the answer is yes.

That is why dropping it into the middle of the garden appears to do nothing — the cat is not touching an edge, so the honest answer is “no”, and the block moves on.

What a bounce actually changes

WHAT IT SHOULD LOOK LIKE

The faded cat is where it started. After the bounce it stands at the edge facing the other way — so the very next move takes it back across the garden.

at the start

step 1 of 2

the sprites move as they would on the real Stage

Watch the Direction box while this happens. Bounce off the right edge and 90 becomes -90. Bounce off the top and 0 becomes 180. The bounce is really just a very well-timed change of heading — the thing you spent all of last lesson learning to control.

The block in a stack


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce

Reset, face right, travel far enough to reach the edge, then bounce.

Order matters, again

The bounce block has to come after the move. Put it before, and it asks its question while the cat is still safely in the middle, gets the answer “no”, and does nothing useful.

Why it matters

Without this block, sprites pile up against the edges and freeze. With it, they keep going forever. Almost every Scratch game with something moving on its own uses it somewhere.

Worked Example — Mei Ling’s bouncing cat 15 min

We build the stuck version first, on purpose, so that the fix is worth having.

WHAT IT SHOULD LOOK LIKE

Stage plan. Out to the edge, then turned round ready to come back. The return only happens once the bounce block is in place.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Step 1 — Reset, face, travel

Build the four-block stack: when flag clicked, go to x: (0) y: (0), point in direction (90), then move (250) steps.


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps

Four blocks. This is the version that gets stuck.

Step 2 — Watch it get stuck

Click the flag. The cat shoots to the right edge and pins there. Read the Direction box: still 90. The cat is facing off the Stage, which is why another click achieves nothing.

Step 3 — Add the bounce

Scroll down the Motion category to if on edge, bounce and snap it on the bottom.

Step 4 — Run it again and read the box

The cat reaches the edge, then flips to face left. The Direction box now reads -90 and the cat itself appears mirrored. Nothing moved — only the heading changed.

Step 5 — Prove the bounce is doing the work

Temporarily drag the go to x: (0) y: (0) and point in direction (90) blocks out of the stack, leaving just the hat, the move and the bounce. Now click the flag repeatedly.

The cat crosses to the right, bounces, crosses back to the left, bounces again, and keeps going with every click. That is the behaviour the whole arc has been heading toward — you are simply supplying the repetition by hand.

Step 6 — Put the reset blocks back

Snap the two reset blocks back on top. A predictable start is worth more than a party trick, and next lesson’s finale depends on it.

What changed: your cat can now meet the end of the garden and deal with it. That was the last thing standing between you and a project that runs by itself.

The full assembled stack (your reference)


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce

Five blocks: reset, face, travel, bounce.

Try It Yourself — three small builds 12 min

🟢 Easy

Goal: Bounce off the left edge instead. Predict what the Direction box will read afterwards before you click.

WHAT IT SHOULD LOOK LIKE

Left edge this time. Write your prediction down before you press the flag.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
go to x: (0) y: (0)
point in direction (-90)
move (250) steps
if on edge, bounce

Think: a bounce turns the heading round. Going in at -90, the cat comes out at 90 — exactly the reverse of the right-edge case.

🟡 Medium

Goal: Bounce off the top. The same block, an edge you have not tried yet.

WHAT IT SHOULD LOOK LIKE

Straight up, into the top edge, and straight back down again.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
go to x: (0) y: (0)
point in direction (0)
move (200) steps
if on edge, bounce

Think: the top edge sits at y = 180, so 200 steps is more than enough. Heading 0 becomes 180 — the cat now points at the ground.

🔴 Stretch

Mini-mission: there and back in one click. Get the cat to cross the garden, bounce, cross all the way back, and bounce again — without you touching the flag a second time.

WHAT IT SHOULD LOOK LIKE

Two edges, two bounces, one flag click. The circles mark where each bounce happens.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

It works if: a single click sends the cat to one edge, turns it round, sends it to the opposite edge, and turns it round again — leaving it facing its original direction. Stay within 8 blocks.

Think: after the first bounce the cat is at one edge facing the other way. How far is it from there to the far edge — and is one move block enough to cover it?

Mini-Challenge — thank the wall 5 min

“The polite cat”

Send the cat into the edge of the garden and have it react — but only after it has turned round, not before.

WHAT IT SHOULD LOOK LIKE

Goal: the bubble should appear with the cat already facing back the way it came.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

It works if:

One flag click runs the whole thing.
The cat visibly reaches an edge and turns round.
The bubble appears after the turn, with the cat facing the new way.
You used only blocks from this lesson and earlier.

Reveal one valid solution (teacher)


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce
say [Terima kasih, dinding!] for (2) seconds

Six blocks. The interesting error is putting the say block before the bounce — it still runs, but the cat speaks while still facing the wall, which is exactly the ordering point.

🚀 Mission — Fence Bouncer

WHAT IT SHOULD LOOK LIKE

One dramatic dash, one bounce, one reaction — and the butterfly gets to watch.

at the start

step 1 of 2

the sprites move as they would on the real Stage

Aiman wants a proper stunt: the cat charges the fence, rebounds off it, and has something to say about the experience.

The cat starts from a known spot and heading, so the stunt is identical every run.
It travels far enough to genuinely reach the edge — not almost.
It rebounds, ending up facing back the way it came.
It reacts in words of your own choosing, once the rebound has happened.
One flag click, 8 blocks or fewer.

✅ Done when: two runs in a row look identical, and the cat is facing back down the garden as it speaks. Going further: add a second dash so it bounces off the far fence too, with a different line.

Teacher notes — one setup that satisfies the brief

Six blocks: hat, go to x: (0) y: (0), point in direction (90), move (250) steps, if on edge, bounce, then a say block. The two most common misses are a move that is too small to reach the edge (so the bounce silently does nothing) and forgetting the reset, which makes the second run behave differently from the first.

Recap 2 min

The bounce block asks one question — am I touching an edge? — and only acts if the answer is yes. When it does act, it turns the sprite’s heading round and nudges it back inside. It has to come after the move, it works on all four edges, and it is the first block you have met that makes a decision instead of just following orders.

if on edge, bounce (block): Turns a sprite’s heading round if it is touching an edge of the Stage. Does nothing if it is not.
Edge: Any of the four borders: left x = −240, right x = 240, top y = 180, bottom y = −180.
Bounce: A change of heading caused by meeting an edge. Right-edge bounce turns 90 into −90.

Homework 1 min

The boomerang cat. One click, two edges, two bounces — and the cat back where it started, facing the way it began.

WHAT IT SHOULD LOOK LIKE

Out to bounce 1, all the way back to bounce 2 — and the heading ends where it began.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Build the seven-block stack below.
Click the flag once and watch both bounces.
Read the Direction box afterwards. It should match what it was at the start.
Screenshot your Script Area.


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce
move (500) steps
if on edge, bounce

Seven blocks. The 500-step move is deliberately more than the width of the Stage.

Bring back next class:

A screenshot of your seven-block Script Area.
Your answer to: “If you deleted the second bounce block, where would the cat end up and which way would it be facing?”

Heads up for next class: SCR-L01-14 is the arc finale. Everything from these eight lessons comes together into one Cat’s Garden Stroll you save and show.

WHAT IT SHOULD LOOK LIKE

Where this arc is heading: everything you have learned becomes one showpiece — the cat crossing the garden.

where the arc is heading

step 1 of 2

the sprites move as they would on the real Stage

Learning Goals 3 min

By the end of this lesson you will be able to:

Explain in your own words what if on edge, bounce checks before it does anything.
Place the block after a move so the cat turns round instead of getting pinned to the edge.
Predict what the Direction box will read after a bounce off any of the four edges.

Warm-Up 7 min

Your cat can go anywhere in the garden and face any way. But there is one thing it still handles badly, and you have probably already seen it happen.

WHAT IT SHOULD LOOK LIKE

Where we are now. Reach the edge and the cat simply stops there, still facing outward. Click again and nothing happens at all.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Quick-fire puzzle

Daniel built this script and clicked the flag three times. The cat began at the centre. What happens on the third click?


when flag clicked
move (200) steps

Two blocks, three clicks, one very determined cat.

Reveal the answer

Click 1 takes the cat from 0 to 200. Click 2 tries for 400, but the Stage stops it at 240. Click 3 does nothing at all — the cat is already against the edge and there is nowhere further to go.

The cat is not broken. It is simply still facing right, with no right left. Today’s block notices that situation and turns it round.

New Concept — bouncing off the edge 15 min

Think of a ball rolling across a room. When it meets the wall it does not stop dead or pass through — it comes back. if on edge, bounce gives your sprite that same behaviour in one block.

Blocks reference

Block	Category	What it does
`if on edge, bounce`	Motion	Checks whether the sprite is touching an edge. If it is, flips the heading round and nudges it back inside. If it is not, does nothing whatsoever.

It asks a question first

This is the first block you have met that decides something. Every block so far has simply done as it was told. This one looks at the Stage first and only acts if the answer is yes.

That is why dropping it into the middle of the garden appears to do nothing — the cat is not touching an edge, so the honest answer is “no”, and the block moves on.

What a bounce actually changes

WHAT IT SHOULD LOOK LIKE

The faded cat is where it started. After the bounce it stands at the edge facing the other way — so the very next move takes it back across the garden.

at the start

step 1 of 2

the sprites move as they would on the real Stage

The block in a stack


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce

Reset, face right, travel far enough to reach the edge, then bounce.

Order matters, again

The bounce block has to come after the move. Put it before, and it asks its question while the cat is still safely in the middle, gets the answer “no”, and does nothing useful.

Why it matters

Without this block, sprites pile up against the edges and freeze. With it, they keep going forever. Almost every Scratch game with something moving on its own uses it somewhere.

Worked Example — Mei Ling’s bouncing cat 15 min

We build the stuck version first, on purpose, so that the fix is worth having.

WHAT IT SHOULD LOOK LIKE

Stage plan. Out to the edge, then turned round ready to come back. The return only happens once the bounce block is in place.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Step 1 — Reset, face, travel

Build the four-block stack: when flag clicked, go to x: (0) y: (0), point in direction (90), then move (250) steps.


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps

Four blocks. This is the version that gets stuck.

Step 2 — Watch it get stuck

Click the flag. The cat shoots to the right edge and pins there. Read the Direction box: still 90. The cat is facing off the Stage, which is why another click achieves nothing.

Step 3 — Add the bounce

Scroll down the Motion category to if on edge, bounce and snap it on the bottom.

Step 4 — Run it again and read the box

The cat reaches the edge, then flips to face left. The Direction box now reads -90 and the cat itself appears mirrored. Nothing moved — only the heading changed.

Step 5 — Prove the bounce is doing the work

Temporarily drag the go to x: (0) y: (0) and point in direction (90) blocks out of the stack, leaving just the hat, the move and the bounce. Now click the flag repeatedly.

Step 6 — Put the reset blocks back

Snap the two reset blocks back on top. A predictable start is worth more than a party trick, and next lesson’s finale depends on it.

What changed: your cat can now meet the end of the garden and deal with it. That was the last thing standing between you and a project that runs by itself.

The full assembled stack (your reference)


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce

Five blocks: reset, face, travel, bounce.

Try It Yourself — three small builds 12 min

🟢 Easy

Goal: Bounce off the left edge instead. Predict what the Direction box will read afterwards before you click.

WHAT IT SHOULD LOOK LIKE

Left edge this time. Write your prediction down before you press the flag.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
go to x: (0) y: (0)
point in direction (-90)
move (250) steps
if on edge, bounce

Think: a bounce turns the heading round. Going in at -90, the cat comes out at 90 — exactly the reverse of the right-edge case.

🟡 Medium

Goal: Bounce off the top. The same block, an edge you have not tried yet.

WHAT IT SHOULD LOOK LIKE

Straight up, into the top edge, and straight back down again.

at the start

step 1 of 2

the sprite moves as it would on the real Stage


when flag clicked
go to x: (0) y: (0)
point in direction (0)
move (200) steps
if on edge, bounce

Think: the top edge sits at y = 180, so 200 steps is more than enough. Heading 0 becomes 180 — the cat now points at the ground.

🔴 Stretch

Mini-mission: there and back in one click. Get the cat to cross the garden, bounce, cross all the way back, and bounce again — without you touching the flag a second time.

WHAT IT SHOULD LOOK LIKE

Two edges, two bounces, one flag click. The circles mark where each bounce happens.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Think: after the first bounce the cat is at one edge facing the other way. How far is it from there to the far edge — and is one move block enough to cover it?

Mini-Challenge — thank the wall 5 min

“The polite cat”

Send the cat into the edge of the garden and have it react — but only after it has turned round, not before.

WHAT IT SHOULD LOOK LIKE

Goal: the bubble should appear with the cat already facing back the way it came.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

It works if:

One flag click runs the whole thing.
The cat visibly reaches an edge and turns round.
The bubble appears after the turn, with the cat facing the new way.
You used only blocks from this lesson and earlier.

Reveal one valid solution (teacher)


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce
say [Terima kasih, dinding!] for (2) seconds

Six blocks. The interesting error is putting the say block before the bounce — it still runs, but the cat speaks while still facing the wall, which is exactly the ordering point.

🚀 Mission — Fence Bouncer

WHAT IT SHOULD LOOK LIKE

One dramatic dash, one bounce, one reaction — and the butterfly gets to watch.

at the start

step 1 of 2

the sprites move as they would on the real Stage

Aiman wants a proper stunt: the cat charges the fence, rebounds off it, and has something to say about the experience.

The cat starts from a known spot and heading, so the stunt is identical every run.
It travels far enough to genuinely reach the edge — not almost.
It rebounds, ending up facing back the way it came.
It reacts in words of your own choosing, once the rebound has happened.
One flag click, 8 blocks or fewer.

Teacher notes — one setup that satisfies the brief

Recap 2 min

if on edge, bounce (block): Turns a sprite’s heading round if it is touching an edge of the Stage. Does nothing if it is not.
Edge: Any of the four borders: left x = −240, right x = 240, top y = 180, bottom y = −180.
Bounce: A change of heading caused by meeting an edge. Right-edge bounce turns 90 into −90.

Homework 1 min

The boomerang cat. One click, two edges, two bounces — and the cat back where it started, facing the way it began.

WHAT IT SHOULD LOOK LIKE

Out to bounce 1, all the way back to bounce 2 — and the heading ends where it began.

at the start

step 1 of 2

the sprite moves as it would on the real Stage

Build the seven-block stack below.
Click the flag once and watch both bounces.
Read the Direction box afterwards. It should match what it was at the start.
Screenshot your Script Area.


when flag clicked
go to x: (0) y: (0)
point in direction (90)
move (250) steps
if on edge, bounce
move (500) steps
if on edge, bounce

Seven blocks. The 500-step move is deliberately more than the width of the Stage.

Bring back next class:

A screenshot of your seven-block Script Area.
Your answer to: “If you deleted the second bounce block, where would the cat end up and which way would it be facing?”

Heads up for next class: SCR-L01-14 is the arc finale. Everything from these eight lessons comes together into one Cat’s Garden Stroll you save and show.