If you're tired of default explosions that feel floaty or weak, learning how to write a custom roblox explosion script knockback is the quickest way to make your game feel more responsive and impactful. We've all been there: you throw a grenade or trigger a C4 charge, and the player just kind of tips over or, worse, stands there like nothing happened. The built-in Roblox explosion object is fine for basic stuff, but if you want that visceral, cinematic push-back, you have to take control of the physics yourself.
Why the default explosion often fails
Roblox has a built-in Explosion object that comes with a property called BlastPressure. In theory, this is supposed to handle the physics of pushing things away. In reality, it's a bit hit-or-miss. Sometimes it sends parts flying at light speed, and other times a player character barely nudges an inch.
The biggest issue is that BlastPressure treats every part the same way based on its mass, but character models (Humanoids) have their own internal physics logic that often resists these forces. If you want a consistent "oomph" every time a bomb goes off, you need to manually calculate the distance between the blast and the player and then apply a specific impulse. It sounds complicated, but once you break down the math, it's actually pretty straightforward.
Setting up the core logic
To get a better roblox explosion script knockback effect, we're going to step away from relying purely on the explosion's internal physics. Instead, we'll use a script to detect who is nearby and then shove them in the opposite direction of the blast.
The first thing you need is a point of origin. This is usually the position of the part that's exploding. From there, you want to find all the players within a certain radius. You could use GetPartBoundsInRadius, which is a newer and more efficient way to check for nearby objects compared to the old Region3 methods.
Once you've got a list of parts inside the blast zone, you need to filter them. You don't want to apply knockback to every single individual limb of a player, or they'll just turn into a pile of confetti. You just want to find the HumanoidRootPart. That's the "anchor" for the character, and if you move that, the whole player goes with it.
The math behind the push
Here is where people usually get stuck, but don't worry—it's just basic vectors. To find the direction the player should fly, you take the player's position and subtract the explosion's position.
local direction = (playerPos - explosionPos).Unit
Using .Unit is the secret sauce here. It gives you a vector with a length of one, basically just pointing the way. Then, you multiply that direction by a force (like 50 or 100) to decide how far they fly. If you want the player to fly upward a bit too—which always looks cooler—you can add a small vertical offset to that direction vector before applying the force.
Using ApplyImpulse for better physics
In the old days of Roblox dev, we used things like BodyVelocity or BodyForce to move players. Those are mostly deprecated now. The modern, much cleaner way to handle a roblox explosion script knockback is by using ApplyImpulse.
ApplyImpulse is great because it doesn't require you to manually clean up objects after the push is done. You just give the part a "kick," and the physics engine handles the rest. However, there's a catch: characters in Roblox are standing upright because of internal "hip height" forces. If you just hit them with an impulse while they're standing, they might just slide.
To get that satisfying "thrown through the air" look, you usually want to set the player's state to Falling or PlatformStand for a split second. This tells the game, "Hey, stop trying to keep this guy on his feet for a moment while he flies through the air."
Adding falloff to the force
A blast shouldn't hit someone ten studs away with the same power as someone standing right on top of it. To make your roblox explosion script knockback feel realistic, you need to implement "falloff."
Basically, you calculate the distance between the player and the center of the explosion. If they're at the very edge of the radius, the force should be tiny. If they're at ground zero, they should be launched across the map. You can do this by dividing the distance by the total radius and then subtracting that from 1. Multiply your final force by this number, and suddenly your explosions feel much more three-dimensional.
Sample script structure
I won't just leave you hanging with math concepts. Here is a rough idea of how you'd structure this in a server script. Imagine this script is inside a Tool or a Part that's meant to explode:
```lua local explosion = Instance.new("Explosion") explosion.Position = bomb.Position explosion.BlastRadius = 15 explosion.BlastPressure = 0 -- We'll handle the pressure ourselves! explosion.Parent = game.Workspace
local radius = 15 local strength = 100
-- Find everyone in range local parts = workspace:GetPartBoundsInRadius(bomb.Position, radius) local hitCharacters = {}
for _, part in pairs(parts) do local character = part.Parent local hrp = character:FindFirstChild("HumanoidRootPart")
if hrp and not hitCharacters[character] then hitCharacters[character] = true -- Don't hit the same guy twice local direction = (hrp.Position - bomb.Position).Unit local distance = (hrp.Position - bomb.Position).Magnitude local forceMultiplier = 1 - (distance / radius) -- Apply the knockback hrp:ApplyImpulse((direction + Vector3.new(0, 0.5, 0)) * strength * forceMultiplier * hrp.AssemblyMass) end end ```
Notice that hrp.AssemblyMass bit? That's important. Heavier objects need more force to move the same distance. By multiplying by the mass, you ensure that a giant boss and a tiny player both react realistically to the blast.
Fine-tuning the "Feel"
Once you've got the basic roblox explosion script knockback working, you'll probably notice it still feels a little "static." Physics is only half the battle; the rest is visual feedback.
One trick I always use is adding a slight camera shake for any player near the blast. You don't even need a complex module for this—just a brief offset to the camera's CFrame can make the explosion feel twice as powerful. Combine that with a good sound effect (maybe one with a bit of bass) and some particle emitters, and you've gone from a generic Roblox game to something that feels professional.
Another thing to consider is the environment. If your explosion is happening in a tight corridor, the knockback might just slam the player into a wall. You can check for this using Raycasting if you want to be really fancy, maybe dealing "impact damage" if they hit a surface at high velocity. That might be overkill for a simple game, but it's those little details that players really appreciate.
Common mistakes to avoid
One mistake I see constantly is running the knockback logic on the client only. While it might look smoother for the player who threw the bomb, the physics won't replicate properly to everyone else. Always handle the actual force application on the server, or use a RemoteEvent to make sure everyone sees the same chaos happening.
Also, watch out for the BlastPressure property I mentioned earlier. If you're writing your own knockback script, set BlastPressure to 0. If you leave it at the default, you'll have two different forces fighting each other—the built-in one and your custom one. It usually results in players glitching out or flying in weird directions.
Lastly, don't forget about "Network Ownership." If you're trying to move a player, the server usually has the right to do that, but for unanchored parts in the workspace, you might run into some stuttering if the server and client are arguing over who owns that part's physics. For player characters, though, ApplyImpulse on the server is generally very reliable.
Wrapping it up
Building a custom roblox explosion script knockback system is one of those projects that pays off immediately. It changes the way combat feels, it makes your world feel more interactive, and it's a great way to practice your vector math.
Don't be afraid to play with the numbers. Maybe you want a "gravity bomb" that pulls players in instead of pushing them out—just flip the direction vector. Or maybe a "shockwave" that only pushes people if they're standing on the ground. Once you have the foundation of detecting players and applying force, the possibilities are pretty much endless. Just keep tweaking until it feels right!