Thinking and Working Scientifically: Models, Investigations and Analysing Results

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Thinking and Working Scientifically (TWS) is how scientists ask questions, plan, measure, and decide what their results mean. In tests it is mixed into almost every question, so these skills earn marks in biology, chemistry, physics, and Earth and space. On this page one investigation — how the number of coils changes the strength of an electromagnet — runs through most of the sections, so you can see every step of real science.

1. Models: analogies, symbols and formulae

An analogy is a comparison between something new and difficult and something familiar that works in a similar way. Scientists use analogies as models: they help us understand, explain and even predict. But an analogy is never exactly the same as the real thing, so every analogy has limitations (ways it does not match).

Using an analogy for a purpose (8TWSm.02): choose the part of the analogy that matches the question. For example: "Use the pipe analogy to explain why adding a second cell makes a bigger current." → A second pump pushes the water harder, so more water flows each second; in the same way two cells push a bigger current round the circuit.

Symbols and formulae (8TWSm.03) are another kind of model: short, exact ways to write scientific ideas that everyone in the world understands.

2. Hypotheses and predictions

A hypothesis is a scientific idea that explains something, for example: "An electromagnet with more coils of wire is stronger, because more turns of current make a stronger magnetic field." A prediction says what you expect to happen in your investigation, and why, using science you know: "I predict that if I double the number of coils, the electromagnet will pick up about twice as many paperclips, because…"

Is it testable? (8TWSp.01) A hypothesis is testable only if you can collect evidence about it by observing or measuring. Opinions (best, prettiest, nicest, more fun) and ideas about things that cannot be measured are not testable.

Evidence supports or contradicts (8TWSp.02). If the results match the prediction, the evidence supports the hypothesis. If they do not, the evidence contradicts it, and the hypothesis may need to change. One investigation never proves a hypothesis for ever: other scientists repeat the work, and new evidence can still change our ideas.

3. Planning investigations

In a fair test you change one variable, measure one variable and keep all the others the same.

Not all investigations can be fair tests (8TWSp.04). Scientists choose the type of enquiry that fits the question:

Choosing equipment (8TWSc.02). Choose an instrument that measures the right quantity, with a suitable range (big enough) and fine enough scale divisions.

4. Risk assessments and working safely

A hazard is something that could cause harm (acid, a flame, hot water). The risk is the chance that harm happens. A risk assessment lists the hazards and how you will control (reduce) the risk. Then you follow it while you work (8TWSp.05, 8TWSc.05).

5. Sorting, classifying and keys

Scientists sort and classify objects, materials and living things by testing (is it magnetic? does it conduct electricity?), by observation (number of legs, leaf shape), by secondary information (books, databases) and by using keys (8TWSc.01). A dichotomous key asks one question at a time with two possible answers (yes/no), until only one thing is left.

Using the key: a leaf is not divided into leaflets and has smooth edges: no → no → B. A leaf has 7 leaflets: yes → yes → C. Making a key: choose features you can see clearly and that split the group into two ("Has it got legs?"), never opinions ("Is it big?" — big compared with what?).

6. Accuracy, precision and repeating measurements

Accurate measurements are close to the true value. Precise measurements are close to each other when you repeat them; a precise instrument has small scale divisions (a thermometer marked every 0.5 °C is more precise than one marked every 2 °C). Accuracy and precision matter because conclusions are only as good as the measurements they are based on (8TWSc.04).

How to measure accurately: read scales at eye level; read a liquid at the bottom of the meniscus; check the balance reads zero before you start; choose an instrument with a suitable scale; start the stopwatch and stop it at exactly the right moments.

Repeating (8TWSc.03). Repeat each measurement (often three times) and calculate a mean. Repeats let you spot anomalous results. Your readings are repeated sufficiently (enough) if the repeats are close together. If they are spread out, do more repeats.

Secondary sources (8TWSc.06). Information from books, websites, adverts and other people's results must be checked. Is it relevant (about exactly your question)? Is it from a reliable source (scientists, a university, an official organisation)? Could it be biased — written by someone who gains from you believing it, such as a company selling a product? Compare several sources.

7. Recording results

Collect enough results (at least five different values of the independent variable, with repeats) and record them in a table as you go (8TWSc.07). Rules: independent variable in the first column; dependent variable in the next columns; units in the headings, not in every box; same number of decimal places in a column.

In the row for 40 coils, trial 2 (7) is far from the other two (12 and 12): it is anomalous, so it is left out of the mean. Mean = (12 + 12) ÷ 2 = 12. A possible cause: some paperclips fell off, or the current was not switched on fully.

8. Presenting results: bar chart or line graph?

1. Put the independent variable on the x-axis (across) and the dependent variable on the y-axis (up).
2. Label both axes with the quantity and unit.
3. Choose an even scale (1, 2, 5 or 10 per square) that uses more than half of the grid.
4. Plot each point as a small cross (×) exactly.
5. Draw a line of best fit (straight or a smooth curve) with roughly equal numbers of points above and below it. Ignore anomalous points when drawing it. Do not join dot to dot.

9. Trends, anomalies, conclusions and evaluation

Describe the trend (8TWSa.02): use the sentence "As the [independent variable] increases, the [dependent variable] increases / decreases", then add numbers. From the graph: "As the number of coils increases from 10 to 60, the number of paperclips increases from 3 to 18. The paperclips increase by 3 for every 10 extra coils (a straight line through the origin)." The point at 40 coils (8 paperclips) is anomalous: it is well below the line.

Was the prediction accurate? (8TWSa.01) Compare the prediction with the results and give a reason. "I predicted that doubling the coils would double the paperclips. My prediction was accurate: 20 coils picked up 6 paperclips and 40 coils picked up 12 (mean values)." If a prediction was not accurate, suggest why — perhaps your scientific idea was incomplete, or there was an error in the measurements.

Conclusion and its limitations (8TWSa.03): a conclusion says what the results show, using the evidence: "The more coils, the stronger the electromagnet." Limitations are the limits of what you can claim: it was only tested from 10 to 60 coils, with one type of nail and one battery; paperclips only measure strength roughly (you cannot pick up half a paperclip).

Evaluate and improve (8TWSa.04): say what went well or badly in the method and suggest a change with a reason. Example: "Use smaller paperclips or measure the force with a newton meter, so the strength can be measured more precisely." "Repeat each reading three times and calculate a mean, so anomalous results can be spotted and the results are more reliable." "Use a variable resistor and ammeter to keep the current the same, so that it is a fair test."

Worked examples

Worked example 1 — using an analogy A teacher says: "An electric circuit is like water flowing round a loop of pipes, pushed by a pump." (a) What is an analogy? [1] (b) In this analogy, what does the pump represent? [1] (c) Give one limitation of this analogy. [1]

1. (a) A comparison with something familiar that works in a similar way, used to help explain a scientific idea.
2. (b) The cell (or battery) — it pushes the current round, as the pump pushes the water.
3. (c) If a pipe breaks, water pours out, but if a wire is cut the electric current does not flow out — it just stops. (Accept other sensible differences.)

Common mistake: in (c), saying what is the same. A limitation is a way the analogy is different from the real thing.

Worked example 2 — testable hypotheses and evidence Omar's hypothesis: "Seeds germinate faster when they are warmer." (a) Is this hypothesis testable? Explain your answer. [1] (b) Seeds at 25 °C germinated in 3 days; seeds at 10 °C took 8 days. Does this evidence support or contradict the hypothesis? [1]

1. (a) Yes: he can change the temperature and measure the time the seeds take to germinate.
2. (b) It supports the hypothesis: the warmer seeds germinated faster (3 days compared with 8 days).
3. Note: say "supports", not "proves". More tests, at more temperatures and with more seeds, would make the evidence stronger.

Worked example 3 — planning Laila investigates how the number of coils affects the strength of an electromagnet. (a) Name the independent and dependent variables. [2] (b) Name two control variables. [2] (c) Write a prediction and give a scientific reason. [2]

1. (a) Independent: the number of coils [1]. Dependent: the number of paperclips picked up [1].
2. (b) Any two: the same nail (core); the same battery / voltage / current; the same type and size of paperclips; the same wire [2].
3. (c) Prediction: more coils will pick up more paperclips [1]. Reason: more turns of wire carrying current make a stronger magnetic field [1].

Common mistake: a prediction with no reason ("It will pick up more") scores only 1 of the 2 marks.

Worked example 4 — repeats, means and anomalies Use the results table in section 7. (a) Which result is anomalous? [1] (b) Calculate the mean for 20 coils. [1] (c) Have the readings been repeated enough? Explain. [1]

1. (a) 40 coils, trial 2 (7 paperclips) — far below 12 and 12.
2. (b) (6 + 5 + 7) ÷ 3 = 18 ÷ 3 = 6 paperclips.
3. (c) Yes: for each number of coils the three repeats are close together (within 1 or 2 paperclips), apart from one anomaly, which was easy to spot.

Worked example 5 — graphs and conclusions Use Laila's graph. (a) Describe the trend. [2] (b) Use the line of best fit to predict the number of paperclips for 35 coils. [1] (c) State one limitation of her conclusion. [1]

1. (a) As the number of coils increases, the number of paperclips increases [1]; from 3 paperclips at 10 coils to 18 at 60 coils / it goes up in proportion (doubling the coils doubles the paperclips) [1].
2. (b) Go up from 35 on the x-axis to the line, then across: 0.3 × 35 = 10.5, so about 10 or 11 paperclips (you cannot pick up half a paperclip).
3. (c) It was only tested between 10 and 60 coils / with one size of nail / with one battery, so we do not know what happens outside these conditions.

Worked example 6 — choosing equipment and improving accuracy Adam needs to measure 8 cm³ of water. He can choose a 10 cm³, a 100 cm³ or a 1000 cm³ measuring cylinder. (a) Which should he choose? Explain. [2] (b) Suggest how he should read the scale. [1]

1. (a) The 10 cm³ cylinder [1]: it has smaller scale divisions (e.g. 0.2 cm³), so the measurement is more precise/accurate; a large cylinder has big divisions and 8 cm³ would only fill the bottom [1].
2. (b) With his eye level with the bottom of the meniscus, on a flat surface.

Practice

All pages in this course

Start here

• Stage 8 Science: The Tests and How to Prepare
• Thinking and Working Scientifically: Models, Investigations and Analysing Results

Biology

• Joints and Antagonistic Muscles
• Blood and Its Components
• Breathing, Gas Exchange and Diffusion in the Lungs
• A Balanced Diet, Energy Stores and Lifestyle
• Aerobic Respiration
• Ecosystems, Bioaccumulation and Invasive Species

Chemistry

• The Structure of the Atom
• Purity, Concentration and Chromatography
• Word Equations, Exothermic and Endothermic Reactions
• The Reactivity of Metals
• Impure Products and Solubility of Salts

Physics

• Speed and Distance–Time Graphs
• Balanced and Unbalanced Forces, and Moments
• Pressure, Particles and Diffusion
• Reflection and Refraction
• Dispersion and Colour
• Magnetic Fields and Electromagnets

Earth and space

• The Earth's Magnetic Field and Earth's Resources
• Climate, Weather and Climate Change
• Galaxies and Asteroids

Practice tests

• Stage 8 Science — Practice Test 1
• Stage 8 Science — Practice Test 2
• Stage 8 Science — Practice Test 3