GCSE Physics Equations: Why Your Child Knows the Formula but Still Loses Marks

Your child knows that:

speed = distance ÷ time

They can tell you:

energy transferred = power × time

They may even recognise most of the equations on the GCSE Physics equation sheet.

Then the test comes back — and they have still lost marks on the calculation questions.

This is incredibly common.

The problem is that knowing a Physics equation and being able to use it correctly in an exam are two different skills.

Here is where those marks usually disappear.

1. They know the equation but cannot recognise when to use it

GCSE Physics questions rarely say:

“Use the power equation now.”

Instead, the equation is hidden inside a situation.

A question might describe an appliance, give an energy transfer and a time, then ask students to calculate power.

Your child has to recognise:

What information have I been given?

What am I being asked to find?

Which equation connects those quantities?

If they only practise equations on worksheets where the topic is already labelled, this decision-making skill never really develops.

That is why exam-question practice matters.

2. Rearranging the equation is the real problem

Sometimes the Physics is fine.

The Algebra is not.

Your child may confidently use:

speed = distance ÷ time

when asked for speed.

But what happens when the question gives speed and time and asks for distance?

GCSE Physics requires students to change the subject of equations, substitute values and solve simple algebraic equations. Official AQA Maths requirements for GCSE Physics.

If rearranging equations is weak, repeatedly memorising the formula will not solve the problem.

Practise using the same equation in different directions.

3. Units are quietly costing marks

This is one of the easiest ways to lose an otherwise straightforward calculation.

A student might be given:

centimetres instead of metres minutes instead of seconds kilojoules instead of joules milliamps instead of amps

Then they substitute the numbers immediately.

The calculator works perfectly.

The answer is still wrong.

Before calculating, your child should ask:

“Are these quantities in the units this equation expects?”

That single habit can recover marks surprisingly quickly.

4. They substitute numbers too quickly

A messy calculation often begins with a messy setup.

Teach your child to write the equation first.

Then substitute.

Then calculate.

For example:

equation

values substituted

answer + unit

Those few lines of working make it easier to spot mistakes and can also show the examiner what method the student was attempting.

Jumping straight to a calculator answer removes that safety net.

5. They rely on the equation sheet too much

For students taking AQA GCSE Physics in 2027, the full Physics Equations Sheet will still be provided in the exam, using the same content as the 2026 version.

That is helpful.

But an equation sheet does not tell your child:

which equation to choose

whether units need converting

how to rearrange it

what the answer physically means

So having the equation in front of them does not remove the need to practise using it.

That is the trap.

6. They forget the unit at the end

Imagine doing all the difficult work correctly and then dropping a mark because the final answer has no unit.

It happens.

Encourage a simple final check:

number + unit + sensible answer

Does a speed of 500,000 m/s make sense for the situation?

Does the calculated time seem reasonable?

Students who pause for five seconds to check their answer often catch mistakes before moving on.

7. The Maths underneath Physics may be weak

Physics exposes weak Maths very quickly.

AQA's GCSE Physics requirements include standard form, ratios, significant figures, rearranging equations, substitution and interpreting graphs.

So when a student repeatedly struggles with equation questions, the solution may not be more Physics revision.

They may need help with:

basic Algebra standard form unit conversions calculator skills * significant figures

This is why looking at how your child answered the question matters more than simply seeing that it was wrong.

A quick way to diagnose the problem

Take five GCSE Physics calculation questions.

For every incorrect answer, label the mistake:

Wrong equation

Could not rearrange

Wrong substitution

Unit conversion

Calculator error

Forgot unit

You will often discover that the same problem appears repeatedly.

That becomes the next thing to fix.

If your child is struggling more broadly before their mocks, read our guide to helping a child who is struggling with GCSE Physics.

Stop memorising. Start applying.

Knowing equations is useful.

But students improve when they can look at an unfamiliar problem and think:

“I know what this question is giving me, I know what it wants, and I know which equation connects the two.”

That is the skill GCSE Physics is really testing.

Is your child still losing marks on GCSE Physics calculations?

At OTA Learning Studio, we help students move beyond simply memorising equations.

Lessons can target the exact areas causing problems — from rearranging formulas and unit conversions to calculation questions, graphs and exam technique.

If your child knows the content but their Physics marks still do not reflect it, you can book a free parent or student consultation.

Bring a recent test or past-paper attempt.

We can identify why those calculation marks are being lost and work directly on that weakness.