# MU, Source and Sink
Movable Units (MUs) are objects that move freely around in the scene. They can be picked or loaded and they can be placed on Transport Surfaces.[ MUs](https://game4automation.com/documentation/current/mu.html) are created by a [Source](/components-and-scripts/mu-movable-unit/source.md) and deleted by a [Sink](/components-and-scripts/mu-movable-unit/sink.md).
The MU script is automatically attached to all objects created by a [Source](/components-and-scripts/mu-movable-unit/source.md). As a user, you don’t need to interact with the MU script at all, except when the script itself publishes information or requests some input.
This is the Inspector Window for an MU script:
### Properties
**ID, GlobalID (Readonly)**
Each MU automatically receives a global ID (this is globally unique) and a source ID (this is only unique to the Source).
**MU Appearance**
List of differnt MU appearances, used by the [Part Changer](/components-and-scripts/changing-mus/partchanger.md).
**Fixed By (Readonly)**
Fixer/Gripper which is currently fixing the MU.
**Last Fixed By (Readonly)**
Fixer/Gripper which has been fixing the MU last time.
**Loaded On (Readonly)**
MU where this MU is loaded on.
**Standard Parent (Readonly)**
Parent Gameobject before MU has been loaded.
**Parent before Fix (Readonly)**
Parent Gameobject before MU has been Gripped / Fixed.
**Collided with Sensors (Readonly)**
Current Sensors which are colliding with this MU.
**Loaded MUs (Readonly)**
Current loaded MUs on this MU.
**Surface Align Smoothment**
Smoothment parameter for aligning MU with Transport Surface - only used by realvirtual.io Simulation.
**Unfix Speed Interpolate**
Normally, if a Gripper is opening, an MU will directly fall down without a horizontal movement, even if the Gripper has a speed when opening. With this speed interpolate, the speed of movement before opening the Gripper is interpolated and transfered to the MU when opening the Gripper. With this it is possible to “throw” objects.
### Events
Events can be used if your are programming your own scripts and you want to be notified about certain events.
**Event MU Deleted**
Event when the MU is going to be deleted.
**Event MU Is Loaded**
Event when the MU is loaded on another MU.
**Event MU Gets Load**
Event when an MU is loaded on this MU.
**Event MU Sensor**
Event if the MU is colliding with a Sensor.
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