Scratch Project · Grade 5 · Chapter 8

Scratch Mini-Game Part 2: Polish & Scoring

Completing "Space Dodger" — adding collisions, lives, scoring system, broadcasts, and Game Over sound FX!

Learning Goals

What We'll Finish Today

GOAL 1

Collision Sensing

Detect when asteroids hit the player and subtract lives with temporary invincibility.

GOAL 2

Broadcast Messages

Use broadcast [Game Over v] to signal all sprites to stop and switch screens.

GOAL 3

Sound & Polish

Add retro sound effects, score counters, and win/loss backdrops.

Project Recap

What We Built in Part 1

In Part 1, we got Astro-Cat moving smoothly and built the infinite falling asteroid loop. But right now, asteroids pass through Astro-Cat without doing anything!

Today's Goal: Turn our animation into a real, challenging arcade game!

Game Design Story

Making Games Feel Alive

Great games give instant feedback when something important happens — a screen flash, a sound effect, or a score pop-up!

Today we add player lives, collision flashes, explosion sounds, and high score tracking!

Core Concept

Collision Detection Physics

Inside the Asteroid script, we check every frame: "Am I touching Astro-Cat right now?"

      if <touching [AstroCat v]?> then {

        change [lives v] by (-1)

        play sound [Boom v]

        set y to (180) // Reset asteroid back to top

        wait (0.5) seconds // Invincibility delay!

      }

Game Physics Secret

Why We Need Invincibility Frames

1

Collision Hit

Asteroid touches Astro-Cat.

2

Subtract 1 Life

Lives goes from 3 to 2.

3

Pause / Respawn

Asteroid teleports top & waits 0.5s so 3 lives don't vanish in 1 frame!

Scoring Mechanics

How Survival Scoring Works

Every time an asteroid safely reaches the bottom of the screen without hitting the player, award +10 points!

      if <y position < -170> then {

        change [score v] by (10)

        play sound [Pop v]

        set y to (180)

      }

Core Concept

What is a Scratch Broadcast?

A Broadcast is like a radio announcement sent to all sprites and backdrops at once!

📢 Sender Sprite

if then broadcast [Game Over v]

📻 Receiver Sprite / Stage

when I receive [Game Over v] ➔ switch backdrop to [GameOverScreen v], stop [all v]

Visual Flow

The Game Over Chain Reaction

1

Lives Hit 0

Player loses last heart.

2

Broadcast Sent

broadcast [Game Over v] fires.

3

Stage Reacts

Backdrop changes, Game Over sound plays, game freezes.

Stage Code

Stage Game Manager Script

      when green flag clicked

      switch backdrop to [Space v]

      set [score v] to (0)

      set [lives v] to (3)

      when I receive [Game Over v]

      switch backdrop to [Game Over Screen v]

      play sound [Lose Sound v] until done

      stop [all v]

Side-by-Side Comparison

Raw Prototype vs. Polished Arcade Game

❌ RAW PROTOTYPE

No sound effects or visual feedback
Sprites just freeze silently when lost
No high score display

✅ POLISHED ARCADE GAME

Retro sound FX on jump, hit, and score
Clean Game Over screen with final score
Invincibility flash effect on hit

Debunking Myths

The 0-Life Multi-Death Bug

Glitch: When player hits asteroid, lives go from 3 to 0 instantly!

Fix: You must reset the asteroid's position or add wait 0.5 secs inside the collision block so the sprite doesn't register 30 touches per second!

Smartboard Voting

Which Broadcast Block to Use?

We want the Stage to wait until the Game Over sound finishes before stopping all scripts.

Option A: broadcast [Game Over v]

Option B: broadcast [Game Over v] and wait

Vote: Thumbs UP for Option A, Thumbs DOWN for Option B!

Spot the Bug

Why Is the High Score Vanishing?

when green flag clicked ➔ set [HighScore v] to (0)

Bug Analysis: Why should HighScore NOT be reset to 0 at green flag click? What variable SHOULD reset to 0 instead?

Think-Pair-Share

Adding Star Power-Ups

Design a golden Star sprite that falls from top twice per game!

Partner Task: IF Astro-Cat touches the Star, what cool effect should happen? (+1 Extra Life? 5 seconds of invincibility? +50 points?)

Guided Practice

Connecting Broadcasts & Sounds Live

Let's finish the game scripts live on the smartboard!

Step 1: Add score (+10) on safe asteroid drop.
Step 2: Add collision check (-1 life & boom sound).
Step 3: Create Game Over backdrop & broadcast receiver script.

Game Testing

Peer Playtesting Protocol

Swapping seats with a classmate to test game balance!

1. Is it too hard?

If tester dies in under 3 seconds, decrease asteroid speed!

2. Is it too easy?

If tester gets 500 points easily, add a 2nd asteroid!

3. Are there bugs?

Check if scores reset correctly on replay.

Hands-on Challenge

The Speed Boost Level Up!

Mission: Add an if 100> conditional that speeds up falling asteroids from Y change (-6) to Y change (-12)!

Scratch Goal: Make the game get progressively harder as score increases!

Quick Check · Question 1

Why do we put a `wait (0.5) seconds` block after losing a life in collision detection?

ATo slow down background music

BTo give the player temporary invincibility so they don't lose 3 lives in one instant hit

CTo make the sprite change color

DScratch requires all scripts to pause

Click to reveal answer

Quick Check · Question 2

Which Scratch block allows one sprite to trigger actions across ALL other sprites and backdrops?

Achange size by (10)

Bbroadcast [message v]

Cpoint in direction (90)

Dask [name?] and wait