As the title suggest, I have two questions :
Is there anything physically different about the vocal chords (or parts of the human anatomy responsible for voice) that gives them the ability to do different voices / accents ?
What’s the physics of the ability to do different voices ? Like is it the length of the vocal chords/ their elasticity / the lungs ability to hold or discharge air, the ability to move your tongue around, etc ?
All humans have the ability to produce many different sounds with our vocal chords-- That’s inherent in the ability to talk. Some languages tend to use some sounds more than others, and so speakers of those languages get more practice in making those sounds, which is what leads to accents. But all humans are capable of all of them, and some go out of their way to practice some sounds to be better at some accents.
From a physics point of view, air passing the vocal chords creates the initial sound, which is then modified by the vocal track, tongue and mouth shape.
These elements form a series of resonant filters, and people can learn to control some of these elements (to a greater or lesser extent).
Changing mouth shape is easy, and can make a significant change to the sound of a voice. Tightening the tongue and upper throat changes the resonance of the mouth, soft palate and nasal cavity. This is often used to achieve a falsetto. Relaxing these elements allows more bass and slop into the produced sound.
One of the major changes is to the vocal formants. These are specific resonances related to vowel sounds, and are controlled by the length and size of the vocal tract. It is formants that (generally) allow us to distinguish between male, female and children’s voices - if the formants are higher, the vocal tract is shorter, indicating a woman or child. When a male voice is sped up and lifted an octave or more, you get a “chipmunk” effect - the formants are indicating an impossibly short vocal tract. Playing a track like Dolly Parton “Jolene” at a slow speed (45 rpm recording at 33 1/3 rpm) seriously sounds like a male voice.
For a voice actor, controlling the vocal tract musculature to shift formants is essential to change a voice into a different character.
Related question: do actors have to listen to recordings of themselves in order to perfect accents? As anyone who has head recordings of their own voice knows, the voice we hear in our heads when we talk is nothing like the voice that other people hear.