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Game Physics 101: Adding Gravity and Jumping to Your 2D Game

In the last post, we implemented basic player movement, sprite rendering, collision detection, and boundary control. Now, let’s bring our game world closer to reality by introducing gravity and jumping mechanics. These are fundamental for platformers and any game that involves vertical movement or physics-based behavior.

Why Gravity and Jumping Matter

Gravity gives your game world a sense of realism and challenge. Without it, players would float unnaturally or remain static in mid-air. Jumping, on the other hand, adds an essential layer of gameplay, letting players avoid obstacles, reach new areas, or interact with elements above them.

Let’s dive into how to implement both with a simple velocity and acceleration system.

Implementing Gravity: Making the Player Fall

First, we’ll simulate gravity by adding vertical velocity and applying it every frame. We’ll also define a ground level so the player doesn’t fall forever.

Code Snippet:

# Gravity and ground level
gravity = 0.5
player_velocity_y = 0
on_ground = False
GROUND_LEVEL = HEIGHT - 50  # Bottom of the screen

# Inside game loop
player_velocity_y += gravity  # Apply gravity
player_pos.y += player_velocity_y  # Apply velocity to position

# Check for ground collision
if player_pos.y >= GROUND_LEVEL:
    player_pos.y = GROUND_LEVEL
    player_velocity_y = 0
    on_ground = True
else:
    on_ground = False

Explanation:

  • gravity is a constant force pulling the player down.

  • player_velocity_y tracks how fast the player is falling.

  • We apply gravity every frame and update the player’s vertical position.

  • When the player reaches the ground level, their velocity is reset and they’re flagged as on_ground.

Adding Jumping Mechanic

Next, let’s enable the player to jump, but only when they’re on the ground.

Code Snippet:

# Jump strength
JUMP_FORCE = -10

# Inside input handling section
if keys[pygame.K_SPACE] and on_ground:
    player_velocity_y = JUMP_FORCE
    on_ground = False

Explanation:

  • We check if the spacebar is pressed and if the player is on the ground.

  • Applying a negative velocity (JUMP_FORCE) makes the player go up.

  • Gravity will eventually bring them back down.

Final Result: A Basic Platformer Feel

With gravity and jumping implemented: ✔ The player falls naturally when not on the ground.
✅ Pressing the spacebar makes the player jump.
✅ Gravity pulls them back down, creating a smooth arc.

This simple mechanic opens the door to even more exciting movement systems.

In the next post, we’ll take things up a notch with advanced jump mechanics — including variable jump height, smoother fall speeds, and wall-jumping basics. Stay tuned!

💫   Related Article

Understanding the Game Loop: A Beginner’s Guide to Game Programming Basics
Game Loop in Action: Adding Player Movement, Sprites, and Collision Detection

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