Here's why:
* No moving parts: While it has a rotating function, it doesn't have any internal mechanisms like gears, motors, or levers that would qualify it as a machine.
* Limited function: Its sole purpose is to open and close a door, which is a simple and repetitive action.
* Energy input: It relies on external force (your hand turning it) to operate.
However, the entire door locking system, including the doorknob, the latch, the strike plate, and the keyhole, can be considered a simple machine because it uses mechanical advantage to perform a task.
