How to Create Physics-Based Games in Scratch: Complete Beginner Guide

Want to build games with realistic gravity, bouncing, and collisions? This comprehensive guide shows you exactly how to create physics-based games in Scratch using proven techniques that make your projects feel professional and fun to play.

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What Are Physics-Based Games in Scratch?

Physics-based games simulate real-world mechanics like gravity, momentum, friction, and collisions. Instead of simply moving sprites with arrow keys, physics engines create natural, realistic movement that responds to forces.

Examples of physics-based games:

• Platformers – Characters jump, fall, and land with realistic gravity
• Angry Birds-style games – Objects fly through the air and crash into targets
• Marble run simulators – Balls roll down ramps and bounce off obstacles
• Bridge builders – Structures react to weight and collapse realistically
• Ragdoll games – Characters move with joint physics and momentum

Why learn physics in Scratch? It transforms simple games into engaging experiences where movement feels real and unpredictable outcomes create replayability.

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The 4 Core Physics Concepts

Before coding, understand these fundamental physics principles:

1. Velocity

What it is: How fast and in what direction something moves

In Scratch:

set [x velocity] to (5)  // Moving right at 5 pixels/frame
set [y velocity] to (-3) // Moving down at 3 pixels/frame

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2. Acceleration

What it is: How velocity changes over time

In Scratch:

change [y velocity] by (-1)  // Gravity pulls down

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3. Friction

What it is: Forces that slow down movement

In Scratch:

set [x velocity] to ((x velocity) * (0.9))  // Reduces speed by 10%

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4. Collision

What it is: What happens when objects touch

In Scratch:

if <touching [ground]?> then
  set [y velocity] to (0)  // Stop falling
end

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Method 1: Basic Gravity System (Easiest Start)

Let’s build the simplest physics system – gravity that makes sprites fall.

Setup: Create Variables

// Create these variables for your sprite:
y velocity

Basic Gravity Code

when green flag clicked
set [y velocity] to (0)
forever
  // Apply gravity
  change [y velocity] by (-1)
  
  // Move sprite
  change y by (y velocity)
  
  // Ground collision
  if <touching [ground]?> then
    set [y velocity] to (0)
    
    // Position sprite on top of ground
    repeat until <not <touching [ground]?>>
      change y by (1)
    end
  end
end

What each part does:

• change [y velocity] by (-1) – Gravity constantly pulls down
• change y by (y velocity) – Applies the falling speed
• Ground collision – Stops falling when touching ground

Result: Your sprite falls naturally and lands on platforms!

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Method 2: Platformer Physics Engine

Build a complete physics system for platformer games with jumping, momentum, and collision.

Required Variables

x velocity  // Horizontal speed
y velocity  // Vertical speed
on ground   // Boolean: touching ground or not

Complete Platformer Code

when green flag clicked
set [x velocity] to (0)
set [y velocity] to (0)
go to x: (-200) y: (0)
forever
  // === HORIZONTAL MOVEMENT ===
  if <key [right arrow] pressed?> then
    change [x velocity] by (1)
  end
  if <key [left arrow] pressed?> then
    change [x velocity] by (-1)
  end
  
  // Speed limit
  if <(x velocity) > [8]> then
    set [x velocity] to (8)
  end
  if <(x velocity) < [-8]> then
    set [x velocity] to (-8)
  end
  
  // Apply horizontal movement
  change x by (x velocity)
  
  // Horizontal collision
  if <touching [wall]?> then
    change x by ((0) - (x velocity))
    set [x velocity] to (0)
  end
  
  // Friction
  set [x velocity] to ((x velocity) * (0.85))
  
  // === VERTICAL MOVEMENT (GRAVITY) ===
  change [y velocity] by (-1)  // Gravity
  
  // Apply vertical movement
  change y by (y velocity)
  
  // Ground collision
  if <touching [ground]?> then
    // Stop falling
    repeat until <not <touching [ground]?>>
      change y by (1)
    end
    set [y velocity] to (0)
    set [on ground] to [true]
  else
    set [on ground] to [false]
  end
  
  // === JUMPING ===
  if <<key [space] pressed?> and <(on ground) = [true]>> then
    set [y velocity] to (15)  // Jump strength
  end
end

Features included:

• ✅ Smooth acceleration and deceleration
• ✅ Realistic gravity
• ✅ Jump only when on ground
• ✅ Wall collision response
• ✅ Speed limits prevent too-fast movement

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Method 3: Bouncing Physics

Create objects that bounce realistically off surfaces.

Bouncing Ball Code

when green flag clicked
set [x velocity] to (5)
set [y velocity] to (0)
forever
  // Gravity
  change [y velocity] by (-1)
  
  // Movement
  change x by (x velocity)
  change y by (y velocity)
  
  // Ground bounce
  if <touching [ground]?> then
    // Move out of ground
    repeat until <not <touching [ground]?>>
      change y by (1)
    end
    
    // Reverse and reduce velocity (bounce)
    set [y velocity] to ((y velocity) * (-0.7))
    
    // Stop bouncing if too slow
    if <([abs v] of (y velocity)) < [2]> then
      set [y velocity] to (0)
    end
  end
  
  // Wall bounce
  if <touching [wall]?> then
    set [x velocity] to ((x velocity) * (-0.8))
  end
  
  // Air resistance
  set [x velocity] to ((x velocity) * (0.99))
end

Physics principles:

• Multiplying by -0.7 reverses direction and reduces energy (bounce loses height)
• abs function checks if bounce is too weak to continue
• Air resistance gradually slows horizontal motion

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Method 4: Projectile Physics (Angry Birds Style)

Launch objects that follow realistic arc trajectories.

Launch Mechanic Setup

Variables needed:

x velocity
y velocity
launch power
launch angle

Projectile Launch Code

// === AIMING PHASE ===
when green flag clicked
set [launch power] to (0)
forever
  // Aim with mouse
  point towards [mouse-pointer]
  set [launch angle] to (direction)
  
  // Charge power
  if <mouse down?> then
    change [launch power] by (1)
    if <(launch power) > [20]> then
      set [launch power] to (20)
    end
  end
end

// === LAUNCH ===
when [space] key pressed
set [x velocity] to ((launch power) * ([cos v] of (launch angle)))
set [y velocity] to ((launch power) * ([sin v] of (launch angle)))
broadcast [launch projectile]

// === FLIGHT PHYSICS ===
when I receive [launch projectile]
repeat until <touching [ground]?>
  // Gravity
  change [y velocity] by (-0.5)
  
  // Movement
  change x by (x velocity)
  change y by (y velocity)
  
  // Air resistance
  set [x velocity] to ((x velocity) * (0.98))
  
  // Rotation follows trajectory
  point in direction ((90) + ([atan v] of ((y velocity) / (x velocity))))
end

How it works:

• cos and sin convert angle to X/Y components
• Gravity constantly pulls down during flight
• Air resistance slightly slows horizontal motion
• Sprite rotates to face direction of travel

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Method 5: Advanced – Slope Physics

Make sprites realistically climb and slide down ramps.

Slope Detection Code

when green flag clicked
set [x velocity] to (0)
set [y velocity] to (0)
forever
  // Basic movement code here...
  
  change x by (x velocity)
  
  // === SLOPE HANDLING ===
  if <touching [ground]?> then
    // Try to climb slope
    set [slope height] to (0)
    repeat (8)
      change y by (1)
      change [slope height] by (1)
      
      // If not touching anymore, we climbed the slope
      if <not <touching [ground]?>> then
        stop [this script]
      end
    end
    
    // Slope too steep - push back
    change y by ((0) - (slope height))
    change x by ((0) - (x velocity))
    set [x velocity] to (0)
  end
end

How slope detection works:

1. Move horizontally
2. If touching ground, try moving up (climbing slope)
3. If can climb within 8 pixels, stay on slope
4. If too steep, push sprite back and stop movement

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Creating a Complete Physics Engine

Combine all concepts into one reusable custom block.

Master Physics Custom Block

Step 1: Create Custom Block

• Go to My Blocks
• Make a Block called “physics engine”
• Add inputs: friction, bounce, gravity
• Enable “Run without screen refresh”

Step 2: Define the Block

define physics engine (friction) (bounce) (gravity)

// === GRAVITY ===
change [y velocity] by ((0) - (gravity))

// === APPLY MOVEMENT ===
change x by (x velocity)
change y by (y velocity)

// === HORIZONTAL COLLISION ===
if <touching [wall]?> then
  repeat until <not <touching [wall]?>>
    change x by (([abs v] of (x velocity)) / ((x velocity) * (-1)))
  end
  set [x velocity] to (0)
end

// === VERTICAL COLLISION ===
if <touching [ground]?> then
  repeat until <not <touching [ground]?>>
    change y by (1)
  end
  
  // Bounce
  if <([abs v] of (y velocity)) > [2]> then
    set [y velocity] to ((y velocity) * ((0) - (bounce)))
  else
    set [y velocity] to (0)
  end
end

// === FRICTION ===
set [x velocity] to ((x velocity) * (friction))

Step 3: Use the Block

when green flag clicked
forever
  physics engine (0.9) (0.7) (1) ::custom
  // 0.9 = 90% friction (10% slowdown)
  // 0.7 = 70% bounce (loses 30% energy)
  // 1 = gravity strength
end

Advantages:

• One block handles all physics
• Easy to adjust parameters
• Reusable across multiple sprites
• Clean, organized code

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Adding Realistic Features

Feature 1: Terminal Velocity

Prevent objects from falling infinitely fast.

// In your forever loop:
change [y velocity] by (-1)  // Gravity

// Limit fall speed
if <(y velocity) < [-15]> then
  set [y velocity] to (-15)
end

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Feature 2: Coyote Time

Allow jumping briefly after leaving platform (feels more responsive).

when green flag clicked
set [coyote timer] to (0)
forever
  if <touching [ground]?> then
    set [on ground] to (true)
    set [coyote timer] to (5)  // 5 frames grace period
  else
    set [on ground] to (false)
    change [coyote timer] by (-1)
  end
  
  // Can jump if recently on ground
  if <<key [space] pressed?> and <(coyote timer) > [0]>> then
    set [y velocity] to (15)
    set [coyote timer] to (0)
  end
end

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Feature 3: Jump Buffering

Register jump input slightly before landing.

when green flag clicked
set [jump buffer] to (0)
forever
  // Detect jump button
  if <key [space] pressed?> then
    set [jump buffer] to (5)  // Remember for 5 frames
  else
    change [jump buffer] by (-1)
  end
  
  // Land on ground
  if <touching [ground]?> then
    // If jump was pressed recently, jump now
    if <(jump buffer) > [0]> then
      set [y velocity] to (15)
      set [jump buffer] to (0)
    end
  end
end

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Physics for Different Game Types

Puzzle Physics Games

Examples: Cut the Rope, World of Goo

Key features:

• Swinging/rope physics
• Object stacking
• Weight and balance

Basic rope swing code:

when green flag clicked
set [rope length] to (100)
set [angle] to (0)
set [angular velocity] to (0)
forever
  // Pendulum physics
  set [angular velocity] to ((angular velocity) + (([sin v] of (angle)) * (0.1)))
  change [angle] by (angular velocity)
  
  // Damping (energy loss)
  set [angular velocity] to ((angular velocity) * (0.99))
  
  // Position at end of rope
  set x to ((anchor x) + ((rope length) * ([cos v] of (angle))))
  set y to ((anchor y) + ((rope length) * ([sin v] of (angle))))
end

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Racing Games

Key features:

• Acceleration/deceleration
• Steering
• Drifting

Basic car physics:

when green flag clicked
set [speed] to (0)
set [direction] to (90)
forever
  // Acceleration
  if <key [up arrow] pressed?> then
    change [speed] by (0.5)
  end
  
  // Braking
  if <key [down arrow] pressed?> then
    change [speed] by (-0.8)
  end
  
  // Speed limits
  if <(speed) > [10]> then
    set [speed] to (10)
  end
  if <(speed) < [-5]> then
    set [speed] to (-5)
  end
  
  // Steering (only works when moving)
  if <key [right arrow] pressed?> then
    change [direction] by ((speed) / (2))
  end
  if <key [left arrow] pressed?> then
    change [direction] by ((0) - ((speed) / (2)))
  end
  
  // Movement
  point in direction (direction)
  move (speed) steps
  
  // Friction
  set [speed] to ((speed) * (0.95))
end

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Destruction Physics

Examples: Angry Birds, Demolish

Key features:

• Breaking structures
• Debris physics
• Impact forces

Basic structure collapse:

// For each block in structure:
when I receive [impact]
if <(impact force) > [5]> then
  // Break into pieces
  repeat (5)
    create clone of [debris]
  end
  hide
end

// Debris physics:
when I start as a clone
set [x velocity] to (pick random (-5) to (5))
set [y velocity] to (pick random (5) to (10))
show
repeat until <touching [ground]?>
  physics engine (0.9) (0.5) (1) ::custom
end
wait (2) seconds
delete this clone

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Common Physics Problems & Solutions

Problem 1: Sprite Falls Through Ground

Symptoms: Character passes through solid platforms.

Cause: Moving too fast in one frame.

Solution: Pixel-perfect collision

// Instead of this:
change y by (y velocity)

// Do this:
repeat ([abs v] of (y velocity))
  change y by (([abs v] of (y velocity)) / (y velocity))
  if <touching [ground]?> then
    change y by ((([abs v] of (y velocity)) / (y velocity)) * (-1))
    set [y velocity] to (0)
    stop [this script]
  end
end

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Problem 2: Jittery/Shaky Movement

Symptoms: Sprite vibrates on ground.

Cause: Constant collision checks fighting with movement.

Solution: Collision tolerance

if <touching [ground]?> then
  repeat until <not <touching [ground]?>>
    change y by (1)
  end
  // Only stop if moving downward
  if <(y velocity) < [0]> then
    set [y velocity] to (0)
  end
end

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Problem 3: Can’t Jump on Moving Platforms

Symptoms: Character slides off moving surfaces.

Cause: Platform moves but character doesn’t inherit velocity.

Solution: Platform velocity transfer

// In platform sprite:
when green flag clicked
set [platform x velocity] to (2)
forever
  change x by (platform x velocity)
  if <on edge, bounce> then
    set [platform x velocity] to ((platform x velocity) * (-1))
  end
end

// In player sprite:
if <touching [platform]?> then
  change x by (platform x velocity)
end

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Problem 4: Unrealistic Bouncing

Symptoms: Objects bounce forever at same height.

Cause: Not losing energy on bounce.

Solution: Energy loss coefficient

if <touching [ground]?> then
  set [y velocity] to ((y velocity) * (-0.7))  // Loses 30% energy
  
  // Stop if bounce too weak
  if <([abs v] of (y velocity)) < [1]> then
    set [y velocity] to (0)
  end
end

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Optimization Tips

Tip 1: Use “Run Without Screen Refresh”

For custom blocks handling physics:

✅ Enable in custom block settings

Benefit: Significant performance boost.

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Tip 2: Limit Clone Count

// Before creating clone:
if <(clone count) < [50]> then
  create clone of [debris]
  change [clone count] by (1)
end

// When deleting clone:
when I start as a clone
// ... physics code ...
delete this clone
change [clone count] by (-1)

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Tip 3: Simplify Collision Shapes

Instead of complex costumes:

• Use simple hitboxes
• Circle collisions for balls
• Rectangle collisions for platforms

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Testing Your Physics Engine

Checklist for Realistic Physics

☐ Gravity feels right

• [ ] Objects accelerate downward naturally
• [ ] Terminal velocity prevents infinite speed
• [ ] Jump height feels good

☐ Collisions work properly

• [ ] No passing through solid objects
• [ ] Bouncing loses energy appropriately
• [ ] Slopes can be climbed

☐ Movement feels responsive

• [ ] No input lag
• [ ] Friction provides control
• [ ] Acceleration/deceleration smooth

☐ Performance is good

• [ ] No lag with multiple moving objects
• [ ] Stable 30 FPS
• [ ] Clone count managed

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Real Project Example: Complete Physics Platformer

Here’s everything combined into one working game:

// === SETUP ===
when green flag clicked
set [x velocity] to (0)
set [y velocity] to (0)
set [on ground] to (false)
go to x: (-200) y: (50)
forever
  handle movement ::custom
  apply physics ::custom
end

// === MOVEMENT CUSTOM BLOCK ===
define handle movement
// Horizontal input
if <key [right arrow] pressed?> then
  change [x velocity] by (1)
end
if <key [left arrow] pressed?> then
  change [x velocity] by (-1)
end

// Speed limit
if <(x velocity) > [8]> then
  set [x velocity] to (8)
end
if <(x velocity) < [-8]> then
  set [x velocity] to (-8)
end

// Jumping
if <<key [space] pressed?> and <(on ground) = [true]>> then
  set [y velocity] to (15)
end

// === PHYSICS CUSTOM BLOCK ===
define apply physics
// Gravity
change [y velocity] by (-1)

// Terminal velocity
if <(y velocity) < [-20]> then
  set [y velocity] to (-20)
end

// Apply movement
change x by (x velocity)
change y by (y velocity)

// Horizontal collision
if <touching [wall]?> then
  change x by ((0) - (x velocity))
  set [x velocity] to (0)
end

// Vertical collision
set [on ground] to (false)
if <touching [ground]?> then
  repeat until <not <touching [ground]?>>
    change y by (1)
  end
  set [y velocity] to (0)
  set [on ground] to (true)
end

// Friction
set [x velocity] to ((x velocity) * (0.85))

// Death condition
if <(y position) < [-180]> then
  go to x: (-200) y: (50)
  set [x velocity] to (0)
  set [y velocity] to (0)
end

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Key Takeaways

Essential physics concepts:

1. Velocity – Speed and direction of movement
2. Acceleration – Changes to velocity (gravity, thrust)
3. Friction – Gradual slowdown
4. Collision – Response when objects touch

The physics formula:

Gravity + Velocity + Collision + Friction = Realistic Movement

Best practices:

• Start simple (just gravity), add complexity gradually
• Use custom blocks for reusable physics code
• Test collision detection thoroughly
• Add polish (coyote time, jump buffering)
• Optimize for performance

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Related Tutorials

Continue learning:

• How to Move Sprite Smoothly in Scratch – Master movement basics first
• How to Use Broadcast Message in Scratch – Coordinate physics across sprites
• How to Make Shadow Milk Scratch Game – Complete game project

For young learners: At ItsMyBot, we teach physics concepts through engaging game projects designed for kids aged 5-15. From basic gravity to advanced collision systems, we break down complex concepts into fun, manageable lessons.

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Next Steps

Beginner projects:

• Simple bouncing ball simulator
• Basic platformer with jumping
• Rolling ball down ramps

Intermediate projects:

• Angry Birds clone with projectile physics
• Car racing game with drift mechanics
• Physics puzzle game with ropes/springs

Advanced projects:

• Full destruction physics sandbox
• Complex platformer with advanced movement
• Multiplayer physics-based sports game

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Ready to master game development?

At ItsMyBot, we turn screen time into skill time through personalized, industry-level courses. From Scratch physics to Python game engines and robotics—we help kids aged 5-15 build real skills through hands-on creation.