MassMotion

MassMotion is a Minecraft Fabric mod that introduces realistic, inventory-based physics. The more weight you carry, the more it affects your movement, jumping, swimming, and overall survivability.

Designed to feel immersive without being punishing, MassMotion integrates seamlessly into normal gameplay and is fully configurable.

Features

Inventory Weight System

Over 500 items assigned realistic mass values

Inventory mass is recalculated in real time

Soft cap system prevents extreme or unplayable penalties

Physics Effects

Movement Speed: Carrying heavy items slows you down (up to 35%)

Jump Height: Reduced jump height under heavy loads (up to 25%)

Swimming Speed: Heavier players swim more slowly (up to 50%)

Knockback Resistance: Increased resistance when carrying more weight (up to 50%)

Fall Damage: Heavier players take increased fall damage (up to 50%)

Enchantments

Inertia (Levels I–III)

Reduces movement speed penalties from heavy inventories

Applicable to any armor piece

Each level reduces the speed penalty by 8%

Buoyancy (Level I)

Improves swimming and jumping while carrying heavy items

Applicable to boots only

Reduces jump and swim penalties by 90%

HUD Display

Real-time total inventory mass

Load percentage with color coding (green → yellow → orange → red)

Current movement speed percentage

Displays active enchantment bonuses

Configuration

All features can be customized via config/massmotion.json, including:

Mass soft cap

Strength of movement, jump, swim, and fall penalties

Enchantment bonus values

HUD enable/disable toggle

Installation

Install Fabric Loader for Minecraft 1.21.11

Download and install Fabric API

Download the MassMotion mod JAR

Place both JAR files into your .minecraft/mods folder

Launch Minecraft using the Fabric profile

Requirements

Minecraft 1.21.11

Fabric Loader 0.15.0+

Fabric API

Java 21+

Usage

Testing the Physics

Gold Blocks (22.5 mass each): Reach the soft cap with just a few blocks

Netherite Blocks: Extremely heavy, useful for stress testing

Light items like feathers or bread have minimal impact

Getting Enchantments

Available through Enchanting Tables

Can appear in Librarian villager trades

Enchanted books are accessible in Creative Mode

Configuration Example

{ "massSoftCap": 140.0, "inertiaStrength": 0.35, "inertiaEnchantBonus": 0.08, "jumpPenalty": 0.25, "buoyancyJumpBonus": 0.15, "knockbackResistanceMax": 0.5, "fallDamageIncreaseMax": 0.5, "swimPenaltyMax": 0.5, "enableHud": true }

Server Compatibility

MassMotion works on dedicated servers. Clients do not need the mod installed unless the HUD is enabled.

License

This project is licensed under the MIT License.

Credits

Created by BlueViper