An 'animation' tick can be (and should be) disconnected from the physics 'tick'. Physics/game logic 'ticks' should use a constant time so the simulation is more predictable and stable, a 'animation tick' can be exactly what the monitor refresh rate is and thus doesnt need 'interpolation between ticks'.
It's important to be precise. The position of a small subset of the "objects" are determined by the physics engine. You might have a character with 100s of thousands of vertices, but only a single capsule is in the physics engine. The movement of the characters fingers is not determined by the physics system.
