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Realistic physics based on inventory weight
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.
Over 500 items assigned realistic mass values
Inventory mass is recalculated in real time
Soft cap system prevents extreme or unplayable penalties
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%)
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%
Real-time total inventory mass
Load percentage with color coding (green → yellow → orange → red)
Current movement speed percentage
Displays active enchantment bonuses
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
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
Minecraft 1.21.11
Fabric Loader 0.15.0+
Fabric API
Java 21+
Usage
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
{
"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
}
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