Cat Bounce Across the Stage — Scratch L1

This is the project you complete and ship today — one green-flag click sends the cat gliding to the right fence, bouncing back, and coming to rest where it started.

Learning Goals 3 min

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

Assemble six blocks — when ⚑ clicked, point in direction, glide, if on edge, bounce — into a single working script.
Click the green flag and watch the cat glide right, bounce, glide left, then bounce again.
Edit at least one number in the script (glide time, target x, or direction) and predict how the bounce will change.

Warm-Up 7 min

Over eight lessons you have collected every part: smooth motion (glide), facing a direction (point in direction), and edge-bouncing (if on edge, bounce). Today we glue them all together into the finished arc showpiece — and then ship it.

Quick-fire puzzle — name the missing block

Here is a 5-block script. There is one block missing between "glide" and "glide" that we definitely need today. Which block is it, and why?


when flag clicked
point in direction (90)
glide (2) secs to x: (200) y: (0)
glide (2) secs to x: (-200) y: (0)

A near-working script. Missing one block in the middle.

Reveal the answer

The missing block is if on edge, bounce. After the first glide, the cat sits at the right edge of the Stage facing right. Without a bounce, the cat would still be facing right when the second glide starts — it would awkwardly slide backwards. Adding if on edge, bounce flips it to face left first, so the second glide travels "forward" the way the cat is now facing.

Today's project adds exactly that block — and a second bounce at the other end.

New Concept — putting the cluster together 15 min

The four blocks of this cluster (B · Motion Blocks) each do one tiny job. On their own they barely matter. Snapped together in the right order, they make a sprite feel alive. Think of it like cooking — flour, eggs, butter, sugar are nothing on their own; mixed in the right order, you get a cake.

Blocks reference (everything we have so far)

Block	Category	Job in today's project
when ⚑ clicked	Events (yellow)	Starts the whole script when the user clicks the green flag.
point in direction (90)	Motion (blue)	Faces the cat right at the start, so the first glide travels "forward".
glide (2) secs to x: (200) y: (0)	Motion (blue)	Slides the cat smoothly from where it is to the right-edge target over 2 seconds.
if on edge, bounce	Motion (blue)	Flips direction by 180° when the cat hits an edge. Used twice — once at each end.

The plan on the Stage

The plan in pictures. Glide right (2s), bounce, glide left (2s), bounce. Total run time: about 4 seconds.

Why this is a project lesson

For three lessons we have been learning one block at a time. Today is different — instead of one new block, we are combining four blocks you already know into a single, complete animation. Project lessons are where the cluster becomes a finished thing you can show off.

Guided Build — Mei Ling's bouncing cat 15 min

Open Scratch. Rename the cat to Mei Ling's Cat using the Sprite Properties bar. Make sure the cat sits roughly in the middle of the Stage.

Stage plan for today's build. Script the cat sprite (see ✏️ badge). One click: glide right → bounce → glide left → bounce back to home. Total run time: about 4 seconds.

Step 1 — Add the start hat

Drag when ⚑ clicked from the yellow Events category into the Script Area.

Step 2 — Face the cat right

From the blue Motion category, drag point in direction (90) and snap it under the hat. 90 means right — that is the direction the first glide will travel "forward" along.

Step 3 — First glide: race to the right edge

Drag glide (1) secs to x: (0) y: (0) under the point block. Change secs to 2, x to 200, y to 0. Click the flag once — the cat slides smoothly to the right side. It is now close to the right edge.

Step 4 — First bounce

Drag if on edge, bounce under the glide. The cat is now touching (or very near) the right edge, so the bounce flips its direction from 90 to -90. The cat now faces left.


when flag clicked
point in direction (90)
glide (2) secs to x: (200) y: (0)
if on edge, bounce

After Step 4 — the cat glides right then flips to face left. Click the flag once and watch.

Step 5 — Second glide: race back to the left edge

Drag another glide (1) secs to x: (0) y: (0) under the bounce. Change secs to 2, x to -200, y to 0. The cat now glides smoothly to the left side.

Step 6 — Second bounce

Drag one more if on edge, bounce at the very bottom. The cat hits the left edge and flips direction back to 90 (facing right) — ready for another round-trip on the next click.

Step 7 — Click the green flag

Watch the full animation. The cat glides right (2 seconds), bounces, glides left (2 seconds), bounces. Total: about 4 seconds. Click again — the cat does another full round-trip.

What changed: last lesson, you had one bounce in a script. Today, you have two bounces — and the cat travels the full Stage width between them. With one flag click, the cat completes a full there-and-back journey.

The full assembled stack (your reference)


when flag clicked
point in direction (90)
glide (2) secs to x: (200) y: (0)
if on edge, bounce
glide (2) secs to x: (-200) y: (0)
if on edge, bounce

The Cat Bounce Across the Stage project — six blocks, one click, two bounces, smooth motion both ways. Inside our 8-block L1 cap.

Try It Yourself — extend the project 12 min

🟢 Easy

Goal: Add a cheerful shout in the middle of the trip. Snap a say block between the two glides so the cat says something at the right edge.


when flag clicked
point in direction (90)
glide (2) secs to x: (200) y: (0)
if on edge, bounce
say [Bounce!] for (1) seconds
glide (2) secs to x: (-200) y: (0)
if on edge, bounce

Think: Seven blocks now — still inside the 8-block cap. The total run time goes from 4 seconds to 5 seconds because the say adds 1 second.

🟡 Medium

Goal: Make the cat much slower. Change both glide times to 5 seconds and watch the trip become a long, lazy stroll.


when flag clicked
point in direction (90)
glide (5) secs to x: (200) y: (0)
if on edge, bounce
glide (5) secs to x: (-200) y: (0)
if on edge, bounce

Think: The same six blocks now take 10 seconds. Compare with 1 sec each — the trip flashes by in 2 seconds. Glide time is your speed control.

🔴 Stretch

Goal: Bounce off the top and bottom edges instead of left and right.


when flag clicked
point in direction (0)
glide (2) secs to x: (0) y: (150)
if on edge, bounce
glide (2) secs to x: (0) y: (-150)
if on edge, bounce

Think: Direction 0 = up. Glide to (0, 150) heads upward to the top edge. The bounce flips direction to 180 (down). The cat then glides to (0, -150) and bounces off the bottom. Same idea, different axis.

Mini-Challenge — add a new sprite or rule 5 min

"Two cats bouncing past each other"

Add a second sprite (the Sprite library has plenty — try the orange "Cat 2" or any animal). Give it a similar bouncing script, but make it start at the opposite end and travel the other way. The two sprites should pass each other in the middle.

It works if:

One click of the green flag starts both sprites moving.
Sprite 1 (cat) starts on the left and bounces toward the right.
Sprite 2 (new sprite) starts on the right and bounces toward the left.
You only use blocks from today and earlier lessons (no repeat, no forever).

Reveal one valid solution

Both scripts use the same six blocks, but the second sprite faces the opposite direction at the start.


when flag clicked
point in direction (90)
glide (2) secs to x: (200) y: (0)
if on edge, bounce
glide (2) secs to x: (-200) y: (0)
if on edge, bounce

Sprite 1 script (the cat). Lives on the cat sprite. Starts at the centre, faces right.


when flag clicked
point in direction (-90)
glide (2) secs to x: (-200) y: (0)
if on edge, bounce
glide (2) secs to x: (200) y: (0)
if on edge, bounce

Sprite 2 script. Lives on the new sprite. Starts facing left and glides left first.

Click the cat's card in the Sprite list to attach the first script; click the new sprite's card to attach the second. Click the flag — both scripts run at once because every sprite hears the green flag.

🚀 Mission — Showtime Polish & Ship

Before you share your project, add one small finishing flourish so it feels complete. Then save it properly.

Step 1 — add a polish touch. Pick one of these (or your own idea):

Snap a say [Here I go!] for (1) seconds block right after the hat — the cat shouts as it sets off.
Snap a say [Made it!] for (1) seconds block at the very end — the cat celebrates landing back home.
Switch the cat's costume to a walking pose just before the first glide, then switch back at the end.

Step 2 — save your project. Go to File → Save to your computer. Scratch saves a .sb3 file to your Downloads folder. Keep this file safe — it is your finished project.

Step 3 — share (optional, 13+ or parent email required). If you have a scratch.mit.edu account, click Share at the top of the Scratch editor. Copy the link and bring it to class. If you are under 13, you need a parent's email address to make an account — the .sb3 file is a perfectly good fallback. Show the file in class instead.

✅ Done when: the cat does its full bounce round-trip on one green-flag click, has at least one polish touch, AND you have saved a .sb3 file (or a share link). Going further: write a one-line project note describing your garden — click the "Instructions" field on your Scratch project page and type one sentence about what the cat is doing.

Recap 2 min

Today you assembled the whole B-cluster of motion blocks into one short, polished animation. Hat block to start. Point in direction to set "forward". Glide to slide smoothly. Bounce to flip at the edge. Repeat the glide-bounce pair to come back. Six blocks, one click, a complete cat round-trip.

Project: A complete tiny artefact you can run and show off. Different from a single concept lesson — projects assemble several blocks together.
Round-trip: A there-and-back animation. In today's project: glide right, bounce, glide left, bounce — back where you started.
Cluster: A group of related lessons that build toward one shared outcome. Today's project is the capstone of cluster B (Motion Blocks).

Homework 1 min

Faster, slower, taller. Take today's six-block project and change two of its numbers. Hand in a screenshot of the modified script.

Open the Scratch project you built in class.
Change both glide secs values. Try 0.5 (super fast) or 4 (slow).
Change both glide target y values from 0 to 120. Now the cat bounces along the upper half of the Stage instead of the middle.
Click the flag and watch.

Bring back next class:

A screenshot of your modified 6-block Script Area.
Your written answer to this question: "Why does the cat still bounce at y = 120 instead of going off the top? Is y = 120 close to a top or bottom edge?"

Heads up for next class: SCR-L01-15 revisits when ⚑ clicked in detail and opens the C cluster: Events & Repeats. By SCR-L01-19 you will finally meet repeat (10), the block that loops your cat-bounce automatically without you clicking the flag again.