Physics is the subject where memorising equations works for a while and then stops abruptly. A student who knows what velocity is can reason through an unfamiliar problem; a student who knows that v equals s over t can only match questions to remembered shapes. The second approach carries through lower secondary and fails from Sec 3 onward.
What “understanding a quantity” actually means
This sounds abstract and is concrete in practice.
Take acceleration. A student with recall knows the formula and can substitute. A student with understanding knows acceleration is how fast the velocity is changing — and therefore knows, without a formula, that an object slowing down has acceleration opposite to its motion, that constant speed around a circle still involves acceleration, and that a steeper velocity-time gradient means more of it.
Every one of those is a marked exam point, and none requires the equation.
The same applies throughout. A student who understands that current is a flow of charge can reason about a circuit they have not seen. A student holding V equals IR can only handle circuits shaped like the ones they practised.
Where the recall approach breaks
Multi-step problems. When a question requires three linked steps, formula-matching fails because no single formula is signposted. The student must decide what is happening physically first.
Unfamiliar contexts. Exam questions deliberately dress principles in new scenarios. Recall students freeze; understanding students recognise the underlying situation.
Explain questions. “Explain why the reading decreases” cannot be answered by substitution. It requires describing a mechanism, and a student who never built the mechanism has nothing to say.
Anything involving direction. Vectors, forces, fields. Sign conventions and direction are where formula-matching produces confidently wrong answers.
How to tell which approach your child is using
Ask them to explain a result without any numbers.
“Why does a heavier object not fall faster?” or “Why does the bulb dim when you add another in series?” A student with understanding will reason it through, possibly imperfectly. A student with recall will either state a formula or say they would need the values.
That difference predicts how they will cope from Sec 3 onward far better than their current mark does.
Rebuilding understanding when recall has been the method
This is worth being realistic about: it is slower than learning more formulas, and it is the only thing that works past a certain point.
Start from the physical situation. Before any equation, ask what is happening — what is moving, what is pushing, what is flowing. Students trained on formulas skip this step entirely and it is the step that makes unfamiliar problems tractable.
Draw everything. Free-body diagrams, circuit redraws, ray diagrams. Drawing forces a student to commit to what they think is happening, which exposes misunderstanding immediately.
Ask “what would happen if” constantly. If the mass doubled, if the resistance halved, if the angle increased. Understanding predicts; recall cannot.
Check that answers are sensible. A student who understands notices when a number is absurd. One who is substituting does not, which is why unreasonable answers survive to the mark scheme.
The mathematics underneath
A caveat that matters. Sometimes what looks like a physics problem is a maths problem — the student sets up correctly and loses it in the algebra.
The test is whether they can explain the physics of a question they got wrong. If they can, the physics is fine and the manipulation is the bottleneck, and drilling physics will not fix it. This is a common and expensive misdiagnosis at both O-Level and H2.
Where Singapore students most often stall
Sec 3 mechanics, because it looks familiar from lower secondary and is not — the problems are multi-step and the maths is heavier.
Electricity, because it is invisible and intuitions are weak. Students who never built a mental model of what current and voltage are struggle disproportionately here.
Anything with direction, as above.
None of these requires more hours. All of them respond to the shift from recall to mechanism, which is why identifying which approach the student is using matters more than adding sessions.
Units are the cheapest diagnostic available
There is a fast way to tell whether a student is reasoning or recalling, and it costs nothing.
Ask what the units mean. A student who understands that acceleration is measured in metres per second per second — a change of speed, per second — is holding the concept. A student who knows the symbol and the unit as a pair, with nothing between them, is holding a label.
Units also catch errors that nothing else catches. If a rearranged equation produces an answer in the wrong units, the rearrangement was wrong, regardless of how tidy the algebra looked. Students who carry units through their working find their own mistakes; students who track only numbers do not.
The habit worth building: write units at every step, not just on the final answer. It slows work down slightly and it converts a whole class of invisible errors into visible ones.
Where the recall approach breaks first
The collapse is not uniform across topics, and knowing the order helps you catch it early.
Anything requiring a chain of two or more relationships. A single formula can be recalled. A problem that needs one result fed into a second relationship cannot, because there is no memorised pattern for the combination.
Anything where the same quantity appears in different forms. Energy is the usual first casualty — kinetic, potential, work done, power over time. A student who has learned each as a separate formula has no way to see that they are describing the same thing.
Anything requiring a sign or direction decision. Recall gives magnitudes. Whether something is positive or negative depends on understanding what the quantity represents and which way you defined as positive.
Anything phrased unfamiliarly. A question about a lift accelerating upward is the same physics as a question about a mass on a scale, and a recall-based student sees two unrelated problems.
If a student is comfortable everywhere except these four places, the diagnosis is settled — and the remedy is rebuilding understanding, not more formula practice.
Frequently asked questions
My child memorises all the formulas and still fails. Why? Because the exam mostly does not test formula recall. It tests whether the student can work out what is physically happening and then apply the right relationship. Formula recall is necessary and far from sufficient.
Is physics or chemistry harder? Physics punishes weak mathematics more directly; chemistry punishes imprecise written explanation more. Which is harder depends on the student’s weakness.
Should my child take physics if they dislike maths? It will be a longer road. The mathematics is unavoidable and increases at A-Level. That is worth weighing honestly at the Sec 3 subject-choice point rather than discovering later.
How do I help at home without knowing physics? Ask them to explain things to you without numbers. If they cannot, that is the diagnosis, and it is useful regardless of your own physics knowledge.
When should we get help? When explanation questions start losing marks while calculation questions are fine, or the reverse. Either pattern is informative, and both are easier to address in Sec 3 than in Sec 4.
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