A physics site that had never corrected anything would either not be read, or not be honest. This page exists so that when something here is wrong, there is a public place where it is put right.

What happens next. We rework the problem from scratch rather than checking our own notes. If the fault is ours, the page is corrected and the change is listed below with the date and, unless you would rather not, your name.

If the fault is not ours, we will say so and explain why — which is often more useful than the correction would have been.

None yet. The site is new and has not been announced.

This section is not empty because the material is perfect. It is empty because almost nobody has read it yet. Every correction made from here on will be listed, including the ones nobody would otherwise notice.

12 September 2026  ·  K9 Variable Acceleration, section 4

Example wording only — the limits on the right-hand integral were written as times rather than positions. Corrected. Reported by a reader.

Some parts have more practice than others

Constant acceleration, projectiles and relative motion are well supplied. K1 and K7 are thin. K2 has no practice questions at all — deliberately, since it teaches drawing and a multiple-choice question cannot ask you to find the false claim in a diagram. Its worked-example set does that instead.

No answers are given, and that is a choice

Not an omission. The module spends sixteen parts teaching you to check your own work — rejecting inadmissible roots, differentiating back, holding an answer against the drawing. An answer key would invite checking instead of reasoning. It also means a wrong question leaves you stranded, which is why we would rather hear from you than not.

The worked-example sets are unevenly weighted

Three of the nine cover constraints. That reflects what the source material offered rather than a judgement about difficulty. Every part of the module is now covered by at least one set, and the practice papers are more evenly spread than the worked examples.

• Every practice question is solved independently — never read off a supplied answer key.
• Every diagram is checked against the physics in code, not by eye. A wrong arrow is a false claim about the world, and quieter than a wrong formula.
• Every formula is given with the condition it depends on.
• Where a result can be reached two ways, we check it both ways.

This page is updated whenever anything on the site changes. Last reviewed: the date of the most recent entry above.