Overview
A good IB Physics IA research question is focused and measurable: it names one independent variable you change, one dependent variable you measure, and a specific system — usually in the shape *"How does [independent variable] affect [dependent variable] of [system]?"* The best questions produce numbers you can plot as a graph, compare against a theoretical relationship (ideally a straight line once you linearise it), and report with sensible uncertainties. If you cannot picture the graph before you start, the question is not ready yet. This post is a bank of vetted RQ ideas plus the logic for choosing and sharpening one — it is the topic-selection companion to the full process guide.
What the IB Physics IA is (briefly)
The Internal Assessment is an individual scientific investigation of roughly ten hours built around a research question you choose yourself, marked on personal engagement, exploration, analysis, evaluation, and communication, and worth a fifth of your final Physics grade. This post is only about the first hurdle — landing on a strong question. For structure, criteria bands, uncertainty propagation, and how examiners award marks, read the [IB Physics IA guide](/blog/ib-physics-ia-guide).
What makes a strong research question
For the IB Diploma Programme, every RQ that scores well shares four features:
- Measurable. You can put a number on both the variable you change and the variable you measure, using equipment your school actually has.
- Graphable. The relationship gives you enough data points across a wide enough range to draw a meaningful graph — not two clusters, not a flat line.
- Theory-linked. A known physics relationship predicts what the graph should look like, so you have something concrete to test against rather than just "describing what happened."
- Uncertainty-friendly. You can estimate the uncertainty in each measurement and carry it through, ideally as error bars on the graph.
The trap to avoid is a question that is interesting to read but impossible to quantify. "How does music affect plant growth" is not a Physics IA. "How does the tension in a guitar string affect the frequency of its fundamental note" is.
How to turn an interest into a research question
For the IB Diploma Programme, start with something you genuinely find fun — a sport, an instrument, cooking, cycling — then squeeze it down until only one variable moves. The funnel looks like this:
- Broad interest: basketball.
- Physical phenomenon: the ball bounces.
- Independent variable: drop height.
- Dependent variable: bounce height (or coefficient of restitution).
- RQ: How does drop height affect the coefficient of restitution of a basketball?
Do this funnel on paper for two or three interests, then pick the one with the cleanest graph and the least awkward equipment — it saves you from abandoning a topic three weeks in.
Example research questions by area
For the IB Diploma Programme, each idea below is phrased as a usable RQ with a note on why it works. Adapt the system to whatever you have to hand.
Mechanics
- How does the length of a simple pendulum affect its period? The theory (period proportional to the square root of length) linearises beautifully — plot period squared against length and the gradient gives you g. Cheap, precise, and a classic for a reason.
- How does drop height affect the bounce height (coefficient of restitution) of a ball? Easy to film and measure frame by frame, with a clear expected trend and a nice discussion of energy loss.
- How does launch angle affect the range of a projectile? A small spring launcher or catapult gives a symmetric curve peaking near 45°, which is satisfying to compare against theory.
- How does mass affect the terminal velocity of falling paper cones? Stacking identical cones changes mass while keeping shape constant — a neat way to isolate one variable and discuss drag.
Waves and oscillations
- How does the tension (or length) in a string affect the frequency of a standing wave? A signal generator, vibration driver, and string give you a controllable standing wave; frequency versus the square root of tension linearises well.
- How does water depth affect wave speed? Timing a pulse along a shallow tray tests the shallow-water relationship and works with almost no specialist kit.
- How does the length of an air column affect its resonant frequency? A tube partly filled with water and a tuning fork or speaker lets you probe resonance, with frequency inversely proportional to length.
Electricity and magnetism
- How does the length (or cross-sectional area) of a wire affect its resistance? Resistance is directly proportional to length, giving a clean straight line through the origin and a gradient you can interpret via resistivity.
- How does temperature affect the resistance of a thermistor (or metal wire)? A water bath and thermometer let you map the characteristic curve; the metal-wire version gives a near-linear rise you can quantify.
- How does distance affect the strength of a magnetic field around a wire or magnet? A smartphone magnetometer app or a Hall probe makes this measurable, with a strong inverse relationship to test.
Thermal
- How does surface area (or insulation thickness) affect the cooling rate of water? Log temperature difference against time to test Newton's law of cooling — a good excuse to use a linearised plot.
- What is the specific heat capacity of a metal? An immersion heater, joulemeter, and thermometer let you calculate a value, compare it against the accepted figure, and discuss heat loss in the evaluation.
The value of a linearisable relationship
For the IB Diploma Programme, examiners love a graph that becomes a straight line. If theory says the period of a pendulum is proportional to the square root of length, plotting period *squared* against length turns a curve into a line — and the gradient then hands you a physical constant (here, a value for *g*). A straight-line fit makes it obvious whether your data supports the theory and gives you a clean way to attach uncertainty. When you scout an RQ, ask early: *what can I plot to get a straight line, and what does its gradient mean?*
Common mistakes when choosing a topic
This section covers Common mistakes when choosing a topic — what IB examiners reward most often in past papers and coursework.
- Too broad. "How do bridges work" has no single variable. Narrow until one thing changes.
- No measurable IV or DV. If you cannot attach a number and a unit to what you change and what you measure, stop.
- A relationship too flat, too noisy, or too narrow. Pick variables whose effect is large enough to see above your scatter, and span a wide range with well-spaced points.
- Unsafe or impractical. High voltages, projectiles near people, boiling oil — if the risk assessment scares your teacher, choose another system.
- Copying a standard practical unchanged. Add your own twist so the personal-engagement marks are earned.
How to refine your research question
For the IB Diploma Programme, once you have a rough idea, tighten it with a quick checklist:
- Name the exact system and its range (e.g. "pendulum length from 20 cm to 100 cm in 10 cm steps").
- State the expected theoretical relationship and the graph you will draw.
- Confirm the equipment exists and the biggest uncertainty is manageable.
- Plan repeats to average and estimate random uncertainty, and trim any second variable.
A refined RQ reads like a plan you could hand to another student and get the same experiment back.
How MarkScheme helps
You can draft your question, method, and analysis, then check the wording against IB assessment language rather than guessing what "sufficient" means. [Get an answer or a draft section marked](/mark) for criterion-style feedback, and shore up the underlying physics with the free [IB Physics SL course](/ib/courses/physics-sl) or [HL course](/ib/courses/physics-hl). If you are aiming for the top band overall, pair this with [how to get a 7 in IB Physics](/blog/ib-physics-how-to-get-a-7), and browse the wider [IB guides hub](/guides/ib) for related subjects.
Frequently asked questions
For the IB Diploma Programme, one focused variable you change, one you measure, a specific system, and a known theoretical relationship to test — phrased so you can already picture the graph and attach uncertainties before you collect any data.
What makes a good Physics IA research question?
Do I need a graph in my Physics IA?
In almost every case, yes. A graph — ideally a linearised one where the gradient means something physical — is how you show the relationship, compare it with theory, and display uncertainty. Choosing an RQ that naturally produces one makes the whole analysis easier.
How original does my topic need to be?
You do not need to invent new physics. A standard relationship is fine — the originality comes from your choice of system, your method, and your engagement. A guitar string, a bouncing ball, or a cooling drink can all score full marks with a thoughtful approach.
Can I use a smartphone for data collection?
Yes. Phone sensors (magnetometer, accelerometer), slow-motion video, and free timing or oscilloscope apps are legitimate and often more precise than eye-and-stopwatch methods. Just describe how you used them and estimate their uncertainty.
What if my results do not match the theory?
That is not a failure — it is material for your evaluation. Discuss systematic errors, limitations, and improvements. Examiners reward honest, quantitative reflection far more than a suspiciously perfect result.