Are the player’s body members connected to the HumanoidRootPart

It’s a question like that because when you touch an object with your foot I have the impression that the members of the body use a kind of raycast that goes towards humanoidRootPart

No, there’s not a raycast that happens when you touch an object with your foot.
HumanoidRootPart is the PrimaryPart of the player’s character model, and is the Root of the Humanoid controlling the character.