Cavo vs. vuoto
While both cavo and vuoto can translate to "hollow" or "empty inside" in English, they describe different concepts of emptiness. The word cavo focuses on the physical structure or shape of an object that has a natural or designed cavity. In contrast, vuoto primarily means "empty" and focuses on the temporary or absolute absence of contents, substance, or emotion.
Cavo
The word cavo is used as an adjective to describe physical objects that have an internal cavity, a concave shape, or are structurally hollow by design or nature.
Il vecchio albero nel bosco ha un tronco cavo in cui si rifugiano gli scoiattoli.
(The old tree in the woods has a hollow trunk where squirrels take shelter.)
Le ossa degli uccelli sono cave per essere più leggere durante il volo.
(Bird bones are hollow to be lighter during flight.)
Hanno utilizzato un cilindro d'acciaio cavo per costruire la struttura principale.
(They used a hollow steel cylinder to build the main structure.)
Lo stomaco è considerato un organo cavo del corpo umano.
(The stomach is considered a hollow organ of the human body.)
La statua di bronzo è cava per ridurre il peso e risparmiare materiale.
(The bronze statue is hollow to reduce weight and save material.)
Vuoto
The word vuoto translates generally to "empty" and is used when something lacks contents, is devoid of substance, or produces a hollow sound or feeling.
Ho bussato alla parete e ha prodotto un suono vuoto.
(I knocked on the wall and it produced a hollow sound.)
Quell'uovo di Pasqua è completamente vuoto all'interno.
(That Easter egg is completely hollow on the inside.)
Ha sollevato lo zaino e si è accorto che era vuoto.
(He lifted the backpack and realized it was empty inside.)
Dopo la sua partenza ha sentito un senso di vuoto nel petto.
(After his departure she felt a hollow feeling in her chest.)
Il politico ha fatto solo promesse vuote per ottenere più voti.
(The politician only made hollow promises to get more votes.)
Summary
To summarize, you should use cavo when referring to the permanent, structural shape of an object that features a cavity, such as pipes, bones, or hollowed-out tree trunks. You should use vuoto when pointing out that a container happens to have nothing inside it, or when describing metaphorical emptiness like a hollow sound, empty words, or an emotional void.