The `LinearVelocity` constraint applies force on an assembly to maintain a
**constant** linear velocity. It can be set to apply force along a
`Datatype.Vector3`, line, or 2D&nbsp;plane. Alternatively:

- If you want to control the amount of force applied, use a
  `Class.VectorForce` constraint.
- If you only need **initial** linear velocity, set the
  `Class.BasePart.AssemblyLinearVelocity|AssemblyLinearVelocity` property
  directly on the assembly.

When configuring this constraint, it may be helpful to study
[Roblox Units](/physics/units) to understand how Roblox units
compare to metric units.

#### Relativity

Application of velocity can be controlled through the constraint's
`Class.LinearVelocity.RelativeTo|RelativeTo` property. If set to
`Enum.ActuatorRelativeTo|World`, force will be applied in world coordinates,
independent of the parent or attachment orientations. If set to
`Enum.ActuatorRelativeTo|Attachment0` or
`Enum.ActuatorRelativeTo|Attachment1`, force will be applied relative to
`Class.Constraint.Attachment0|Attachment0` or
`Class.Constraint.Attachment1|Attachment1` respectively.


LinearVelocity

Determines how the constraint force will be limited. When set to
`Enum.ForceLimitMode|Magnitude`, the constraint force will have a
magnitude less than `Class.LinearVelocity.MaxForce|MaxForce`. When set to
`Enum.ForceLimitMode|PerAxis`, the force along each axis will be less than
the corresponding value in
`Class.LinearVelocity.MaxAxesForce|MaxAxesForce` when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
`Enum.VelocityConstraintMode|Vector` or the corresponding value in
`Class.LinearVelocity.MaxPlanarAxesForce|MaxPlanarAxesForce` when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
`Enum.VelocityConstraintMode|Plane`. Only used when
`Class.LinearVelocity.ForceLimitsEnabled|ForceLimitsEnabled` is `true`.


LinearVelocity.ForceLimitMode

Determines how the constraint force will be limited.


Determines if the constraint force will be limited or if the physics
solver can apply an unlimited force to achieve the target velocity. When
enabled, the constraint force is limited based on
`Class.LinearVelocity.ForceLimitMode|ForceLimitMode`. When disabled, the
physics solver will always apply a force that is large enough to achieve
the target velocity.


LinearVelocity.ForceLimitsEnabled

Determines if the constraint force will be limited or if the physics
solver can apply an unlimited force to achieve the target velocity.


The normalized `Datatype.Vector3` direction for constraining the velocity
along a line, when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Line`.


LinearVelocity.LineDirection

The normalized `Datatype.Vector3` direction for constraining the velocity
along a line.


Float value of the velocity when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Line`.


LinearVelocity.LineVelocity

Maximum force along each axis that the constraint can apply to achieve the
target velocity. Only used if
`Class.LinearVelocity.ForceLimitsEnabled|ForceLimitsEnabled` is `true`,
`Class.LinearVelocity.ForceLimitMode|ForceLimitMode` is
`Enum.ForceLimitMode|PerAxis`, and
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
`Enum.VelocityConstraintMode|Vector`. The axes used to apply the limit
correspond to the `Class.LinearVelocity.RelativeTo|RelativeTo` property.


LinearVelocity.MaxAxesForce

Maximum force along each axis that the constraint can apply to achieve the
vector velocity. Only used if
`Class.LinearVelocity.ForceLimitsEnabled|ForceLimitsEnabled` is `true`,
`Class.LinearVelocity.ForceLimitMode|ForceLimitMode` is
`Enum.ForceLimitMode|PerAxis`, and
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
`Enum.VelocityConstraintMode|Vector`.


Maximum magnitude of the force vector the constraint can apply. Only used
if `Class.LinearVelocity.ForceLimitsEnabled|ForceLimitsEnabled` is `true`
and `Class.LinearVelocity.ForceLimitMode|ForceLimitMode` is
`Enum.ForceLimitMode|Magnitude`.


LinearVelocity.MaxForce

Maximum magnitude of the force vector the constraint can apply.


Maximum force along each axis that the constraint can apply to achieve the
plane velocity. Only used if
`Class.LinearVelocity.ForceLimitsEnabled|ForceLimitsEnabled` is `true`,
`Class.LinearVelocity.ForceLimitMode|ForceLimitMode` is
`Enum.ForceLimitMode|PerAxis`, and
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
`Enum.VelocityConstraintMode|Plane`. The axes used to apply the limit
correspond to the `Class.LinearVelocity.RelativeTo|RelativeTo` property.


LinearVelocity.MaxPlanarAxesForce

Maximum force along each axis that the constraint can apply to achieve the
plane velocity. Only used if
`Class.LinearVelocity.ForceLimitsEnabled|ForceLimitsEnabled` is `true`,
`Class.LinearVelocity.ForceLimitMode|ForceLimitMode` is
`Enum.ForceLimitMode|PerAxis`, and
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
`Enum.VelocityConstraintMode|Plane`.


`Datatype.Vector2` value of the velocity in each tangent direction of the
plane, when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Plane`.


LinearVelocity.PlaneVelocity

`Datatype.Vector2` value of the velocity in each tangent direction of the
plane.


The primary axis in the plane, when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Plane`. Value depends on the value of
`Class.LinearVelocity.RelativeTo|RelativeTo` as follows:

- If `Class.LinearVelocity.RelativeTo|RelativeTo` is set to
  `Enum.ActuatorRelativeTo|Attachment0`, this axis is the
  `Class.Attachment.Axis|Axis` of
  `Class.Constraint.Attachment0|Attachment0`.
- If `Class.LinearVelocity.RelativeTo|RelativeTo` is set to
  `Enum.ActuatorRelativeTo|Attachment1`, this axis is the
  `Class.Attachment.Axis|Axis` of
  `Class.Constraint.Attachment1|Attachment1`.
- If `Class.LinearVelocity.RelativeTo|RelativeTo` is set to
  `Enum.ActuatorRelativeTo|World`, this value must be specified in the
  world space.


LinearVelocity.PrimaryTangentAxis

The primary axis in the plane, when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Plane`.


LinearVelocity.ReactionForceEnabled

Sets the `Enum.ActuatorRelativeTo` property for the constraint.


LinearVelocity.RelativeTo

The secondary axis in the plane, when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Plane`. Value depends on the value of
`Class.LinearVelocity.RelativeTo|RelativeTo` as follows:

- If `Class.LinearVelocity.RelativeTo|RelativeTo` is set to
  `Enum.ActuatorRelativeTo|Attachment0`, this axis is the
  `Class.Attachment.SecondaryAxis|SecondaryAxis` of
  `Class.Constraint.Attachment0|Attachment0`.
- If `Class.LinearVelocity.RelativeTo|RelativeTo` is set to
  `Enum.ActuatorRelativeTo|Attachment1`, this axis is the
  `Class.Attachment.SecondaryAxis|SecondaryAxis` of
  `Class.Constraint.Attachment1|Attachment1`.
- If `Class.LinearVelocity.RelativeTo|RelativeTo` is set to
  `Enum.ActuatorRelativeTo|World`, this value must be specified in the
  world space.


LinearVelocity.SecondaryTangentAxis

The secondary axis in the plane, when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Plane`.


`Datatype.Vector3` velocity value when
`Class.LinearVelocity.VelocityConstraintMode|VelocityConstraintMode` is
set to `Enum.VelocityConstraintMode|Vector`.


LinearVelocity.VectorVelocity

The mode of the constraint: `Enum.VelocityConstraintMode|Line`,
`Enum.VelocityConstraintMode|Plane`, or
`Enum.VelocityConstraintMode|Vector`. Default is
`Enum.VelocityConstraintMode|Vector`.


LinearVelocity.VelocityConstraintMode

Applies force on an assembly to maintain a constant linear velocity.


The base class for constraint-based objects. See
[mover constraints](/physics/mover-constraints) and
[mechanical constraints](/physics/mechanical-constraints) for more
details.


Constraint:GetDebugAppliedForce

bodyId

Constraint:GetDebugAppliedTorque

Constraint

This property is `true` if the constraint and both of its parts are in the
`Class.Workspace` and the constraint's `Class.Constraint.Enabled` property
is `true`.


Constraint.Active

Indicates if the constraint is currently active in the world.


The `Class.Attachment` that is connected to `Class.Constraint.Attachment1`


Constraint.Attachment0

The `Class.Attachment` that is connected to
`Class.Constraint.Attachment1`.


The `Class.Attachment` that is connected to `Class.Constraint.Attachment0`


Constraint.Attachment1

The `Class.Attachment` that is connected to
`Class.Constraint.Attachment0`.


Constraint.Color

Toggles whether or not the constraint is enabled.


Constraint.Enabled

Constraint.Visible

The base class for constraint-based objects.


`Instance` is the base class for all classes in the Roblox class hierarchy
which can be part of the `Class.DataModel` tree.

It is not possible to directly create root `Instance` objects, but the special
`Datatype.Instance.new()` constructor creates objects via code, taking the
name of the class as a parameter and returning the created object.


Demonstrates detecting changes to an instance's ancestry by connecting to the `Class.Instance.AncestryChanged` event.

The ChangingPart's Parent is set to different values overtime. The parent of the part is the part's ancestor, so the `Class.Instance.AncestryChanged` event will fire whenever it changes.

Fires when the `Class.Instance.Parent` property of the object or one of
its ancestors is changed.

This event includes two parameters: `child` refers to the `Class.Instance`
whose `Class.Instance.Parent` was actually changed, while `parent` refers
to this instance's new `Class.Instance.Parent`.

You can use this event to track the deletion of an instance in Studio,
such as manual deletion in the Explorer or through a plugin. If you need
to detect when an instance is destroyed using `Class.Instance:Destroy()`,
use the `Class.Instance.Destroying` event instead.


Instance.AncestryChanged

child

The `Class.Instance` whose `Class.Instance.Parent` has been changed.


parent

The new `Class.Instance.Parent` of the `Class.Instance` whose
`Class.Instance.Parent` was changed.


Fires when the `Class.Instance.Parent` property of the object or one of
its ancestors is changed.


This event fires whenever any attribute is changed on the instance,
including when an attribute is set to `nil`. The name of the changed
attribute is passed to the connected function.

For example, the following code snippet connects the `attributeChanged()`
function to fire whenever one of the part's attributes changes:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part

local function attributeChanged(attributeName)
	print(attributeName, "changed")
end

part.AttributeChanged:Connect(attributeChanged)
```

See also `Class.Instance:GetAttributeChangedSignal()` which returns an
event that fires when a specific given attribute changes.


Instance.AttributeChanged

attribute

The name of the attribute that has been changed.


Fires whenever an attribute is changed on the `Class.Instance`.


This snippet prints the names of objects as they are added to the Workspace:

Fires after an object is parented to this `Class.Instance`.

Note, when using this function on a client to detect objects created by
the server it is necessary to use `Class.Instance:WaitForChild()` when
indexing these object's descendants. This is because the object and its
descendants are not guaranteed to replicate from the server to the client
simultaneously. For example:

```
local Workspace = game:GetService("Workspace")

Workspace.ChildAdded:Connect(function(child)
	-- Use WaitForChild() since descendants may not have replicated yet
	local head = child:WaitForChild("Head")
end)
```

Note, this function only works for immediate children of the
`Class.Instance`. For a function that captures all descendants, use
`Class.Instance.DescendantAdded`.

See also `Class.Instance.ChildRemoved`.


Instance.ChildAdded

The `Class.Instance` that has been added.


Fires after an object is parented to this `Class.Instance`.


This snippet prints the names of objects as they are removed from the
Workspace:

Fires after a child is removed from this `Class.Instance`.

Removed refers to when an object's parent is changed from this
`Class.Instance` to something other than this `Class.Instance`. Note, this
event will also fire when a child is destroyed (using
`Class.Instance:Destroy()`) as the destroy function sets an object's
parent to `nil`.

This function only works for immediate children of the `Class.Instance`.
For a function that captures all descendants, use
`Class.Instance.DescendantRemoving`.

See also `Class.Instance.ChildAdded`.


Instance.ChildRemoved

The `Class.Instance` that has been removed.


Fires after a child is removed from this `Class.Instance`.


This following example will print the name of any object that is added to the
Workspace:

This event fires after a descendant is added to the `Class.Instance`.

As it fires for every descendant, parenting an object to the
`Class.Instance` will fire the event for this object and all of its
descendants individually.

If you're only concerned with the **direct children** of the
`Class.Instance`, use `Class.Instance.ChildAdded` instead.

See also `Class.Instance.DescendantRemoving`.


Instance.DescendantAdded

descendant

Fires after a descendant is added to the `Class.Instance`.


The following example prints the name of any descendant as it is being removed
from the Workspace:

This event fires **immediately before** the parent `Class.Instance`
changes such that a **descendant** instance will no longer be a
descendant. `Class.Instance:Destroy()|Destroy()` changes an instance's
`Class.Instance.Parent|Parent` to `nil`, so calling that method on a
descendant of the parent will cause this event to fire.

Since this event fires **before** the descendant's removal, the parent of
the descendant will be unchanged at the time of this event firing. If the
descendant is also a **direct child** of the parent, this event will fire
before `Class.Instance.ChildRemoved`.

If a descendant has children, this event fires with the descendant first,
followed by its descendants.

##### Warning

This event fires with the descendant object that is being removed.
Attempting to set the `Class.Instance.Parent|Parent` of the descendant to
something else will fail. Below is an example that demonstrates this:

```
local Workspace = game:GetService("Workspace")

Workspace.DescendantRemoving:Connect(function(descendant)
	-- Do not manipulate the parent of the descendant in this function!
	-- This event fires BECAUSE the parent was manipulated, and the change hasn't happened yet
	-- Therefore, it is problematic to change the parent like this:
	descendant.Parent = game
end)

local part = Instance.new("Part")
part.Parent = Workspace
part.Parent = nil
```

See also `Class.Instance.DescendantAdded|DescendantAdded`.


Instance.DescendantRemoving

The `Class.Instance` that is being removed.


Fires immediately before a descendant of the `Class.Instance` is removed.


This sample demonstrates how, when using Immediate signal behavior, an Instance being destroyed remains in place until the connected function yields.

This sample demonstrates how, when using Deferred signal behavior,
an Instance is destroyed before the signal fires.

The `Class.Instance` will never be deleted from memory while a connected
function is still using it. However, if the function yields at any point,
the `Class.Instance` and its descendants will be parented to `nil`.

If the `Class.Workspace.SignalBehavior` property is set to
`Enum.SignalBehavior.Immediate`, this event fires immediately before the
`Class.Instance` or one of its ancestors is destroyed with
`Class.Instance:Destroy()`.

If the `Class.Workspace.SignalBehavior` property is set to
`Enum.SignalBehavior.Deferred`, this event fires at the next resumption
point, which will be after the `Class.Instance` or one of its ancestors is
destroyed with `Class.Instance:Destroy()`.

With `Enum.SignalBehavior.Deferred|Deferred` behavior, connecting a script
to its own `Class.Instance.Destroying` event is problematic, as the script
will be destroyed before the callback can be called (meaning it will not
execute).

When deleting an `Class.Instance` in Studio, such as manually deleting
through the [Explorer](/studio/explorer) or through a plugin,
the `Class.Instance` isn't destroyed. Instead, the parent is set to `nil`
which you can track with `Class.Instance.AncestryChanged`.


Instance.Destroying

Fires immediately before (or is deferred until after) the instance is
destroyed via `Class.Instance:Destroy()`.


This event fires whenever any style property is changed on the instance,
including when a property is set to `nil`.

```lua
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local playerGui = player.PlayerGui
local HUDContainer = playerGui:WaitForChild("HUDContainer")
local meterBar = HUDContainer.MeterBar

local function stylePropertyChanged()
	print("Styled properties changed")
end

meterBar:StyledPropertiesChanged():Connect(stylePropertyChanged)
```


Instance.StyledPropertiesChanged

Fires whenever any style property is changed on the instance, including
when a property is set to `nil`.


Instance.childAdded

This method applies a tag to the instance, with no effect if the tag is
already applied. Successfully adding a tag will fire a signal created by
`Class.CollectionService:GetInstanceAddedSignal()` with the given tag.

##### Warnings

- An instance's tags that were added client-side will be dropped if the
  server later adds or removes a tag on that instance because the server
  replicates all tags together and overwrites previous tags.

- When tagging an instance, it is common that some resources are used to
  give the tag its functionality, for example event connections or tables.
  To prevent memory leaks, it's a good idea to clean these up (disconnect,
  set to `nil`, etc.) when no longer needed for a tag. Do this when
  calling `Class.Instance:RemoveTag()`, calling
  `Class.Instance:Destroy()`, or in a function connected to a signal
  returned by `Class.CollectionService:GetInstanceRemovedSignal()`.


Instance:AddTag

This function destroys all of an instance's children and descendants.

```
local part = Instance.new("Part")

-- Add some sparkles
for i = 1, 3 do
	local sparkles = Instance.new("Sparkles")
	sparkles.Parent = part

  local sc = Instance.new("Sparkles")
  sc.Parent = sparkles
end

print("Children:", #part:GetChildren())  --> Children: 3

part:ClearAllChildren()

print("Children:", #part:GetChildren())  --> Children: 0
```

If you do not wish to destroy **all** children and descendants, use either
`Class.Instance:GetChildren()` or `Class.Instance:GetDescendants()` to
loop through those children/descendants and select what to destroy. For
example, the following code sample will destroy all
`Class.BasePart|BaseParts` descending from a `Class.Model`:

```
local Workspace = game:GetService("Workspace")

local model = Workspace:FindFirstChild("TestModel")

for _, descendant in model:GetDescendants() do
	if descendant:IsA("BasePart") then
		descendant:Destroy()
	end
end
```


Instance:ClearAllChildren

This function destroys all of an instance's children.


Demonstrates cloning a model using `Class.Instance:Clone()`.

`Clone()` creates a copy of an instance and all of its descendants,
ignoring all instances that are not
`Class.Instance.Archivable|Archivable`. The copy of the root instance is
returned by this method and its `Class.Instance.Parent|Parent` is set to
`nil`. Note that if the instance itself has
`Class.Instance.Archivable|Archivable` set to `false`, this function will
return `nil`.

If a reference property such as `Class.ObjectValue.Value` is set in a
cloned instance, the value of the copy's property depends on original's
value:

- If a reference property refers to an instance that was **also** cloned,
  the copy will refer to the copy.
- If a reference property refers to an object that was **not** cloned, the
  same value is maintained in the copy.


Instance:Clone

Create a copy of an instance and all its descendants, ignoring instances
that are not `Class.Instance.Archivable|Archivable`.


Demonstrates destroying a Part using the `Class.Instance:Destroy()` function.

This function is the correct way to dispose of objects that are no longer required.

Sets the `Class.Instance.Parent` property to `nil`, locks the
`Class.Instance.Parent` property, disconnects all connections, and calls
`Destroy()` on all children. This function is the correct way to dispose
of objects that are no longer required.

Disposing of unneeded objects is important, since unnecessary objects and
connections in a place use up memory which can lead to serious performance
issues over time.

As a best practice after calling `Destroy()` on an object, set any
variables referencing the object (or its descendants) to `nil`. This
prevents your code from accessing anything to do with the object.

```lua
local part = Instance.new("Part")
part.Name = "Hello, world"
part:Destroy()
-- Don't do this:
print(part.Name)  --> "Hello, world"
-- Do this to prevent the above line from working:
part = nil
```

Once an `Class.Instance` has been destroyed by this method, it cannot be
reused because the `Class.Instance.Parent` property is locked. To
**temporarily** remove an object instead of destroying it, set
`Class.Instance.Parent|Parent` to `nil`. For example:

```
local Workspace = game:GetService("Workspace")

object.Parent = nil
task.wait(2)
object.Parent = Workspace
```

To destroy an object after a set amount of time, use
`Class.Debris:AddItem()`.


Instance:Destroy

Sets the `Class.Instance.Parent` property to `nil`, locks the
`Class.Instance.Parent` property, disconnects all connections, and calls
`Destroy()` on all children.


Returns the first ancestor of the `Class.Instance` whose
`Class.Instance.Name` is equal to the given name.

This function works upwards, meaning it starts at the instance's immediate
`Class.Instance.Parent` and works up towards the `Class.DataModel`. If no
matching ancestor is found, it returns `nil`.

The following code snippet would find the first ancestor of the object
named `Car`.

```
local car = object:FindFirstAncestor("Car")
```

For variants of this function that find ancestors of a specific class,
please see `Class.Instance:FindFirstAncestorOfClass()` and
`Class.Instance:FindFirstAncestorWhichIsA()`.


Instance:FindFirstAncestor

name

The `Class.Instance.Name` to be looked for.


Returns the first ancestor of the `Class.Instance` whose
`Class.Instance.Name` is equal to the given name.


Returns the first ancestor of the `Class.Instance` whose
`Class.Object.ClassName` is equal to the given className.

This function works upwards, meaning it starts at the instance's immediate
`Class.Instance.Parent` and works up towards the `Class.DataModel`. If no
matching ancestor is found, it returns `nil`.

A common use of this function is finding the `Class.Model` a
`Class.BasePart` belongs to. For example:

```
local model = part:FindFirstAncestorOfClass("Model")
```

This function is a variant of `Class.Instance:FindFirstAncestor()` which
checks the `Class.Object.ClassName` property rather than
`Class.Instance.Name`. `Class.Instance:FindFirstAncestorWhichIsA()` also
exists, using the `Class.Object:IsA()` method instead to respect class
inheritance.


Instance:FindFirstAncestorOfClass

className

The `Class.Object.ClassName` to be looked for.


Returns the first ancestor of the `Class.Instance` whose
`Class.Object.ClassName` is equal to the given className.


Returns the first ancestor of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.

This function works upwards, meaning it starts at the instance's immediate
`Class.Instance.Parent` and works up towards the `Class.DataModel`. If no
matching ancestor is found, it returns `nil`.

Unlike `Class.Instance:FindFirstAncestorOfClass()`, this function uses
`Class.Object:IsA()` which respects class inheritance. For example:

```
print(part:IsA("Part"))  --> true
print(part:IsA("BasePart"))  --> true
print(part:IsA("Instance"))  --> true
```

Therefore, the following code sample will return the first
`Class.BasePart` ancestor, regardless of if it is a `Class.WedgePart`,
`Class.MeshPart` or `Class.Part`.

```
local part = object:FindFirstAncestorWhichIsA("BasePart")
```

See also `Class.Instance:FindFirstAncestor()`.


Instance:FindFirstAncestorWhichIsA

Returns the first ancestor of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.


The below would look in Workspace for an object name "Brick". If found, it
will change the name of the object to "Foo".

Returns the first child of the `Class.Instance` with the given name, or
`nil` if no such child exists. If the optional `recursive` argument is
`true`, this function searches all descendants rather than only the
immediate children of the `Class.Instance`.

##### Checking the Existence of an Object

`FindFirstChild()` is necessary if you need to verify an object exists
before continuing. Attempting to index a child by name using the dot
operator throws an error if the child doesn't exist.

```lua
local Workspace = game:GetService("Workspace")

-- The following line errors if the part doesn't exist in the workspace
Workspace.Part.Transparency = 0.5
```

A better approach is to use `FindFirstChild()` to first check for `Part`,
then use an `if` statement to run code that needs it.

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace:FindFirstChild("Part")
if part then
	part.Transparency = 0.5
end
```

##### Finding a Child Whose Name Matches a Property

Sometimes the `Class.Instance.Name|Name` of an object is the same as that
of a property of its `Class.Instance.Parent|Parent`. When using the dot
operator, properties take precedence over children if they share a name.

In the following example, a `Class.Folder` called `Color` is added to a
`Class.Part`, which also has the `Class.Part.Color` property. Notice that
`part.Color` refers to the `Datatype.Color3` property value, not the child
`Class.Folder` instance. A benefit of using
`Class.Instance:FindFirstChild()|FindFirstChild()` is that the
introduction of new properties does not impose a risk on your code.

```lua
local part = Instance.new("Part")
local folder = Instance.new("Folder")
folder.Name = "Color"
folder.Parent = part
local c1 = part.Color  -- The property
local c2 = part:FindFirstChild("Color")  -- The child folder
```

##### Performance Notes

`Class.Instance:FindFirstChild()|FindFirstChild()` takes about 20% longer
than using the dot operator and almost 8 times longer than simply storing
a reference to an object. Therefore, you should avoid calling it in
performance-dependent code such as in tight loops or functions connected
to `Class.RunService.Heartbeat` and `Class.RunService.PreRender`. Instead,
store the result in a variable, or consider using
`Class.Instance.ChildAdded|ChildAdded` or
`Class.Instance:WaitForChild()|WaitForChild()` to detect when a child of a
given name becomes available.


Instance:FindFirstChild

The `Class.Instance.Name` to be searched for.


recursive

Whether or not the search should be conducted recursively.


Returns the first child of the `Class.Instance` found with the given name.


Returns the first child of the `Class.Instance` whose
`Class.Object.ClassName|ClassName` is equal to the given `className`.
Unlike `Class.Instance:FindFirstChildWhichIsA()`, this function only
returns objects whose class matches `className`, ignoring class
inheritance. If no matching child is found, this function returns `nil`.


Instance:FindFirstChildOfClass

Returns the first child of the `Class.Instance` whose
`Class.Object.ClassName|ClassName` is equal to the given class name.


Returns the first child of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.

If no matching child is found, this function returns `nil`. If the
optional recursive argument is true, this function searches all
descendants rather than only the immediate children of the
`Class.Instance`.

Unlike `Class.Instance:FindFirstChildOfClass()`, this function uses
`Class.Object:IsA()` which respects class inheritance. For example:

```lua
print(part:IsA("Part")) --> true
print(part:IsA("BasePart")) --> true
print(part:IsA("Instance")) --> true
```

Therefore, the following code sample will return the first
`Class.BasePart` child, regardless of if it is a `Class.WedgePart`,
`Class.MeshPart` or `Class.Part`.

```
local part = object:FindFirstChildWhichIsA("BasePart")
```

Developers looking for a child by name, should use
`Class.Instance:FindFirstChild()` instead.


Instance:FindFirstChildWhichIsA

The `Class.Object.ClassName` to be searched for.


Returns the first child of the `Class.Instance` for whom
`Class.Object:IsA()` returns true for the given className.


Returns the first descendant found with the given `Class.Instance.Name`.

This method is disabled and cannot be used. To find the first descendant
of an instance, consider using the `recursive` parameter on
`Class.Instance:FindFirstChild()` instead.


Instance:FindFirstDescendant

The `Class.Instance.Name` to search for.


Returns the first descendant found with the given `Class.Instance.Name`.


If the `Class.Instance` is an `Class.Actor`, the `Class.Actor` itself is
returned. Otherwise, its closest ancestor `Class.Actor` is returned. If no
ancestor is an `Class.Actor`, the result is `nil`.


Instance:GetActor

Returns the `Class.Actor` associated with the Instance, if any.


This method returns the value which has been assigned to the given
attribute name. If no attribute has been assigned, `nil` is returned.

For example, the following code snippet sets and then gets the value of
the instance's `InitialPosition` attribute:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part
part:SetAttribute("InitialPosition", part.Position)

local initialPosition = instance:GetAttribute("InitialPosition")
print(initialPosition)
```

##### See Also

- `Class.Instance:SetAttribute()` which sets the attribute with the given
  name to the given value.
- `Class.Instance:GetAttributes()` which returns a dictionary of key‑value
  pairs for each of the instance's attributes.


Instance:GetAttribute

The name of the attribute being retrieved.


The value which has been assigned to the given attribute name. If no
attribute has been assigned, `nil` is returned.


Returns the value which has been assigned to the given attribute name.


This function returns an event that behaves exactly like the
`Class.Object.Changed|Changed` event, except that it only fires when the
specific given attribute changes; effectively it is similar to
`Class.Object:GetPropertyChangedSignal()|GetPropertyChangedSignal()` but
for attributes.

It's generally a good idea to use this method instead of a connection to
`Class.Object.Changed|Changed` with a function that checks the attribute
name. Subsequent calls to this method on the same object with the same
attribute name return the same event.

The following code example returns a signal that fires the function
`attributeChanged()` when the part's `InitialPosition` attribute changes:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part
part:SetAttribute("InitialPosition", part.Position)

local function attributeChanged()
	print("Attribute changed")
end

part:GetAttributeChangedSignal("InitialPosition"):Connect(attributeChanged)
```

See also `Class.Instance.AttributeChanged` which fires whenever any
attribute is changed on the instance.


Instance:GetAttributeChangedSignal

The name of the specified attribute for which the change signal is
being returned.


An event that fires when the given attribute changes.


Returns an event that fires when the given attribute changes.


This method returns a dictionary of key‑value pairs for each attribute
where the key is the attribute's name and the value is a non‑`nil` value.

For example, the following code snippet outputs an instance's attributes
and values:

```lua
local Workspace = game:GetService("Workspace")

local part = Workspace.Part
part:SetAttribute("InitialPosition", part.Position)
part:SetAttribute("CanUse", true)

for name, value in part:GetAttributes() do
	print(name .. " = " .. value)
end
```

See also `Class.Instance:GetAttribute()` which returns the value that has
been assigned to the given attribute name.


Instance:GetAttributes

A dictionary of string → variant pairs for each attribute where the
string is the name of the attribute and the variant is a non-nil
value.


Returns a dictionary of the instance's attributes.


The below would print the name of all objects currently in Workspace when ran.

Returns an array (a numerically indexed table) containing all of the
instance's direct children, or every `Class.Instance` whose
`Class.Instance.Parent|Parent` is equal to the object. The array can be
iterated upon using either a numeric or generic for-loop:

```lua
local Workspace = game:GetService("Workspace")

-- Numeric for-loop example
local children = Workspace:GetChildren()
for i = 1, #children do
	local child = children[i]
	print(child.Name .. " is child number " .. i)
end
```

```lua
local Workspace = game:GetService("Workspace")

-- Generic for-loop example
local children = Workspace:GetChildren()
for i, child in children do
	print(child.Name .. " is child number " .. i)
end
```

The children are sorted by the order in which their
`Class.Instance.Parent|Parent` property was set to the object.

See also the `Class.Instance:GetDescendants()|GetDescendants` function.


Instance:GetChildren

An array containing the instance's children.


Returns an array containing all of the instance's children.


Returns a coded string of the debug ID used internally by Roblox. Note
that:

- This item is protected. Attempting to use it in a `Class.Script` or
  `Class.LocalScript` will cause an error.
- A debug ID is an ID used in debugging processes. It allows a debugger to
  read each instruction before an application processes it. All objects in
  Roblox act like processes and each run instructions (or 'code') that can
  be debugged if needed.
- This can be helpful for plugins which need to distinguish similar
  objects from one-another (such as objects that share the same name).


Instance:GetDebugId

scopeLength

Returns a coded string of the debug ID used internally by Roblox.


GetDescendants is often used to do something to all the descendants that are a
particular type of object. The code in this example uses GetDescendants and
`Class.Instance:IsA()` to find all of the parts in the workspace and turns
them green.

This object method returns an array that contains all of the descendants
of that object. Unlike `Class.Instance:GetChildren()`, which only returns
the immediate children of an object, this method finds every child of the
object, every child of those children, and so on.


Instance:GetDescendants

An array containing the instance's descendants.


Returns an array containing all of the descendants of the instance.


This code sample demonstrates the behavior of `Class.Instance:GetFullName()`.
It shows how the function behaves when called on an object not in the
`DataModel` hierarchy, and it also shows how the return value does not escape
special characters.

This code sample re-implements the `Class.Instance:GetFullName()` function in
Lua.

Returns a string describing the instance's ancestry. The string is a
concatenation of the `Class.Instance.Name|Name` of the object and its
ancestors, separated by periods. The `Class.DataModel` (`game`) is not
considered. For example, a `Class.Part` in the `Class.Workspace` may
return `Class.Workspace.Part`.

When called on an `Class.Instance` that is not a descendant of the
`Class.DataModel`, this function considers all ancestors up to and
including the topmost one without a `Class.Instance.Parent|Parent`.

This function is useful for logging and debugging. You shouldn't attempt
to parse the returned string for any useful operation; this function does
not escape periods (or any other symbol) in object names. In other words,
although its output often appears to be a valid Luau identifier, it is not
guaranteed.


Instance:GetFullName

Returns a string describing the instance's ancestry.


This method returns the styled or explicitly modified value of the
specified property, or else the default property value if it hasn't been
styled/modified. This differs slightly from accessing the property value
directly, such as `[GuiObject].Rotation`, which returns the default or
modified value of the property.

```lua
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local player = Players.LocalPlayer
local playerGui = player.PlayerGui
local HUDContainer = playerGui:WaitForChild("HUDContainer")

local coreSheet = ReplicatedStorage:FindFirstChild("CoreSheet")
local rule = coreSheet:FindFirstChildWhichIsA("StyleRule")
rule.Selector = "TextButton"

-- Reference to a button
local button = HUDContainer:FindFirstChildWhichIsA("TextButton")

print(button:GetStyled("Rotation")) --> 0 (default value)
print(button.Rotation) --> 0 (default value)

-- Apply rotation through style rule property
rule:SetProperty("Rotation", 30)

print(button:GetStyled("Rotation")) --> 30 (styled value based on rule)
print(button.Rotation) --> 0 (default value)

-- Explicitly modify/override styled property
button.Rotation = 45

print(button:GetStyled("Rotation")) --> 45 (modified value)
print(button.Rotation) --> 45 (modified value)
```


Instance:GetStyled

The styled or explicitly modified value of the specified property, or
else the default property value if it hasn't been styled/modified.


Returns the styled or explicitly modified value of the specified property,
or else the default property value if it hasn't been styled/modified.


This method returns an event that behaves exactly like the
`Class.Instance.StyledPropertiesChanged|StyledPropertiesChanged` event,
except that it only fires when the given style property changes. It's
generally a good idea to use this method instead of a connection to
`Class.Instance.StyledPropertiesChanged|StyledPropertiesChanged` with a
function that checks the property name. Subsequent calls to this method on
the same object with the same property name return the same event.

Note that this event will not pass any arguments to a connected function,
so the value of the changed property must be read directly within a
script.

```lua
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local playerGui = player.PlayerGui
local HUDContainer = playerGui:WaitForChild("HUDContainer")
local meterBar = HUDContainer.MeterBar

local function stylePropertyChanged()
	print("Style property changed!")
end

meterBar:GetStyledPropertyChangedSignal("AnchorPoint"):Connect(stylePropertyChanged)
```


Instance:GetStyledPropertyChangedSignal

property

Name of the style property for which to listen for changes.


Event that fires when the given style property changes.


This method returns an array of the tags applied to the given instance, as
strings. You can add tags either in Studio in the
[Properties](/studio/properties) window or at runtime with
`Class.Instance:AddTag()|AddTag()`.

This method is useful when you want to do something with multiple tags on
an instance at once. However, it is inefficient to use this method to
check for the existence of a single tag; instead, use
`Class.Instance:HasTag()|HasTag()` to check for a specific tag.


Instance:GetTags

Gets an array of all tags applied to the instance.


This method returns `true` if the provided tag has been added to the
object. You can add tags either in Studio in the
[Properties](/studio/properties) window or at runtime with
`Class.Instance:AddTag()|AddTag()`.


Instance:HasTag

Check whether the instance has a given tag.


Demonstrates determining if one instance is the ancestor of another using `Class.Instance:IsAncestorOf()`

Workspace and SpawnLocation are ancestors of the SpawnLocation's decal.
Workspace is an ancestor of SpawnLocation.

SpawnLocation and its decal are descendants of Workspace, not ancenstors.
Decal is a descendant to SpawnLocation, not an ancestor.

Returns true if an `Class.Instance` is an ancestor of the given
descendant.

An `Class.Instance` is considered the ancestor of an object if the
object's `Class.Instance.Parent` or one of it's parent's
`Class.Instance.Parent` is set to the `Class.Instance`.

See also, `Class.Instance:IsDescendantOf()`.


Instance:IsAncestorOf

True if the `Class.Instance` is an ancestor of the given descendant.


Returns true if an `Class.Instance` is an ancestor of the given
descendant.


Instance

`Instance` is the base class for all classes in the Roblox class hierarchy
which can be part of the `Class.DataModel` tree.


/reference/engine/classes/LinearVelocity.yaml

LinearVelocity

Summary

Properties

Methods

Events

Properties

ForceLimitMode

ForceLimitsEnabled

LineDirection

LineVelocity

MaxAxesForce

MaxForce

MaxPlanarAxesForce

PlaneVelocity

PrimaryTangentAxis

ReactionForceEnabled

RelativeTo

SecondaryTangentAxis

VectorVelocity

VelocityConstraintMode

Methods

Events