Challenge 2: A Cloth Simulation Looking Frozen When Scrubbed Backward — Solution Walkthrough

The answer:

Per this chapter's own warning box, this is exactly the un-baked
simulation problem it describes. By default, a simulation calculates
forward, frame by frame, from its own starting point — scrubbing
backward without first baking can show an incorrect, frozen, or
inconsistent state, since Blender hasn't actually stored what the
simulation's own result should look like at that earlier frame.

Why the fabric looked correct the first time but not on rewind:

The first, forward playthrough calculated the simulation live, frame
by frame, in the correct order. Once the student scrubbed backward,
Blender wasn't recalculating that earlier state correctly on demand —
it showed whatever frozen or inconsistent result happened to be
available, not a properly recalculated version of that specific
moment.

What fixes this:

Per this chapter's own material, baking the simulation stores its own
result for every frame in advance, so scrubbing to any frame —
forward or backward — shows the already-calculated, correct result for
that specific point, rather than relying on live, forward-only
calculation.

WHY THIS WORKS AS AN ANSWER
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This exercise checks that incorrect behavior when scrubbing backward
is correctly traced back to a missing baking step, per this chapter's
own explicit warning about un-baked simulations.