Table of Contents
Why Anchoring and Collisions Matter
In Roblox Studio, every object in your world follows the rules of physics. Parts can fall, slide, bounce, or stay perfectly still. Two of the most important controls you have over this behavior are anchoring and collisions. Understanding these will let you decide which objects move, which stay fixed in place, and how players and objects interact with each other.
Anchoring tells Roblox whether a part is allowed to move at all. Collisions tell Roblox whether parts can pass through each other or if they should block and push each other. Together, these settings define how solid and stable your world feels.
Anchored vs Unanchored Parts
When a part is unanchored, Roblox applies gravity and other physical forces to it. If you place a block in the air and do not anchor it, it will fall as soon as the game starts. If something pushes it, it will move. If another object hits it, it can be knocked away.
When a part is anchored, Roblox locks it in place. Gravity does not pull it down. Forces and collisions do not move it. The part will stay exactly where you put it in Studio unless you move it with a script. You should think of anchored parts as the fixed structure of your game, such as floors, walls, and platforms.
In the Properties window, a Part has a property called Anchored. When Anchored is checked, the part is locked. When it is unchecked, the part is free to move according to physics. You can select multiple parts at once and toggle Anchored to quickly fix a whole structure.
Important rule: Anything that must not fall, slide, or be knocked over during the game should be anchored.
When to Anchor Parts
You do not want every object to be anchored. Some things need to move for your game to feel alive and interactive. However, most of the environment in beginner projects should be anchored to avoid unexpected physics problems.
Use anchored parts for platforms, floors, walls, decorative buildings, trees, signs, and anything that players stand on or jump to that should never fall. If you forget to anchor a floor in an obby, it might look fine in Studio, but when you press play it can drop out of the world, leaving your character falling forever.
Use unanchored parts for moving objects, like swinging obstacles, rolling balls, crates that can be pushed, or any physical puzzles. For example, if you want a ball to roll downhill when a player touches it, the ball must be unanchored so physics can affect it.
You can also combine anchored and unanchored parts in one design. Imagine a bridge made of fixed supports and a loose hanging part at the end that players can push. The supports stay anchored to keep the bridge stable, and the loose part is unanchored to react to players.
Collisions and CanCollide
Collisions decide whether parts block each other and the player. By default, most parts in Roblox are solid. Your character cannot walk through them, and other parts will not pass through them. This behavior is controlled by a property called CanCollide.
If CanCollide is true, the part acts like a solid object. Players land on it, cannot walk through it, and other parts bounce or stop when they hit it. If you build a wall with CanCollide set to true, players must go around or over it.
If CanCollide is false, the part does not block movement. Players can walk or jump through it, and other parts can pass through as well. The part is still visible and still exists, it simply does not act as a physical barrier. This is useful for effects like ghost platforms, visual guides, or triggers that respond to touch without blocking the player.
In the Properties window, you can find CanCollide for a part and toggle it. Changing this gives you control over which parts are solid and which are not.
Key idea: Anchored controls whether a part moves. CanCollide controls whether a part blocks movement.
Different Combinations of Anchoring and Collisions
Because anchoring and collisions are separate, you can mix their settings to create different behaviors.
An anchored part with CanCollide = true is a normal solid structure that does not move. Floors, platforms, and most buildings in beginner games use this combination.
An anchored part with CanCollide = false is visible but not solid. Players can walk right through it, and it will never move. This is useful for effects like background decorations that you do not want to interfere with movement, or for invisible guiding shapes where you only show a texture or effect but not a solid barrier.
An unanchored part with CanCollide = true is a movable solid object. It can be pushed, knocked over, or fall down, but it still blocks movement. This is good for physics puzzles, falling obstacles, or destructible barriers that topple over when hit.
An unanchored part with CanCollide = false is a moving object that does not block anything. It can pass through players and other parts. This is less common, but sometimes used for visual effects, moving decorations, or special triggers that you want to follow physics without stopping the player.
Collisions Between Different Parts
Collisions do not only affect the player. They also affect how parts behave when they meet each other. If two parts both have CanCollide set to true, they will not overlap. If you drop one unanchored block onto another solid block, it will land on top.
If at least one of the parts has CanCollide set to false, they can overlap without being blocked. This is what allows you to pass through a ghostly object or to hide visual effects inside solid walls. You can create a glowing region inside a wall by placing a non colliding part in the same space as a solid wall part.
Anchoring still matters here. Two unanchored parts with CanCollide = true can stack, slide off each other, or topple as gravity pulls them. If you change one of them to anchored, that one stays fixed while the other moves around it.
Anchoring, Collisions, and Gameplay Feel
The way you use anchoring and collisions changes how your game feels to play. A game where everything is unanchored and solid can quickly become chaotic. Floors might fall, obstacles might tip over, and players might get trapped. On the other hand, a game where everything is anchored and solid might feel very stiff and unresponsive.
Anchoring is usually used to create a stable and predictable environment. Players should be able to rely on certain surfaces and structures always being there. Collisions then define the paths that are open or blocked. You can create challenges by mixing solid and non solid visuals, such as an invisible path of anchored non colliding parts that only reveals its shape through subtle clues.
Because these settings are so important, many creators build a habit of checking Anchored and CanCollide as soon as they place or duplicate parts. You can even temporarily turn off collisions while building in Studio so you can move parts through each other easily, then turn them back on for testing.
Design tip: For beginner projects, anchor almost everything in your environment, and only leave unanchored parts when you intentionally want them to move.
Basic Troubleshooting with Anchors and Collisions
Many early problems in Roblox building come from forgotten anchors or incorrect collision settings. If parts disappear below the map when you press play, they are probably unanchored and falling. If your character gets stuck on decorations, those decorations might have CanCollide set to true when they should not.
If you cannot walk through something that should be just a visual effect, check that its CanCollide is false. If you walk through a platform you thought was solid, check that its CanCollide is true and that the part is really where you think it is. Also check that it is anchored if it should not move when you touch it.
Small adjustments to anchoring and collisions often fix these problems without any scripts. As you build more complex scenes, keep these two properties in mind and you will avoid many common beginner mistakes.