Practical Skills and Scientific Method

How science finds things out

Science does not just collect facts; it tests ideas carefully so that the answers can be trusted. Whatever the subject, the method is the same. You ask a question and make a prediction, then plan a fair test in which you change one thing, measure its effect, and keep everything else the same. You take careful measurements with the right apparatus, repeat them, and record the results in a table. Then you look for a pattern, often by drawing a graph, and finally you write a conclusion and judge how well the test worked. This module covers those skills: variables, fair tests, choosing apparatus, making results reliable, and drawing sound conclusions. These are the practical skills that Unit 4 rewards.

Method words

Learn these five terms before you plan and judge an investigation.

Match each apparatus to what it measures

A fair test against an unfair test

A fair test is the heart of a good investigation. Compare the two approaches.

Which is the independent variable?

A student changes the temperature of some water and measures how quickly sugar dissolves in it. Which is the independent variable?

• The temperature of the water
• How quickly the sugar dissolves
• The amount of sugar used
• The type of cup

Making results you can trust

A single reading can be thrown off by a slip of the hand or a badly read scale, so scientists repeat every measurement. If the repeats give a similar answer the result can be trusted, and adding the repeats and sharing them out evenly gives the best single figure. Sometimes one reading sits far away from all the others; that odd reading is usually a mistake, and it is left out when working out the average rather than allowed to spoil it. Careful reading of the scale, the right apparatus and enough repeats are what turn a rough guess into evidence. When you evaluate an investigation, the first thing to suggest is nearly always more repeats.

Pick the true method facts

Select every statement about a good investigation that is true.

• A fair test changes only one variable at a time
• Repeating readings and taking a mean makes results more reliable
• An anomalous result does not fit the pattern
• The more variables you change at once, the fairer the test
• You should never write your results down

Order the steps of an investigation

Put the stages of a scientific investigation in a sensible order.

• Ask a question and make a prediction
• Plan a fair test and list the variables
• Carry out the test and record the results
• Draw a graph and find the pattern
• Write a conclusion and evaluate the method

Complete the method facts

The variable you deliberately change is the _____ variable. The variable you measure is the _____ variable. Things you keep the same are _____ variables. A reading that does not fit the pattern is an _____ result.

Weighing yourself three times

Imagine stepping onto some bathroom scales and reading the number, then stepping off and back on twice more. The three numbers come out slightly different each time, perhaps because you stood in a slightly different way. If two of them are close together and one is wildly out, you would trust the two that agree and treat the odd one with suspicion. And if you wanted the best single figure, you would add the readings and share them out evenly between them. Scientists do exactly this with every measurement: they repeat it, watch for a reading that looks wrong, and work out an average so that one slip of the hand does not spoil the whole result.

Tap the things kept the same

A student tests how the amount of fertiliser changes plant growth. Tap every thing that should be kept the same.

• the type of plant
• the amount of water given
• the amount of light
• the amount of fertiliser

Work out the mean reading

Three repeat readings of a length are 12, 14 and 13 centimetres. The mean is the total divided by the number of readings. What is the mean length?

Evaluate the investigation

Read each situation and choose the best answer.

• A student took only one reading at each temperature. How could the results be made more reliable?
• One result sits far from the pattern made by all the others. What should the student do?
• A student changed two things at once during the test. What is the problem?

Build a method point

Choose the word for each gap to complete one accurate point about a fair test.

Explain how to plan a fair test

A friend is about to do a science experiment for the first time and asks how to make it a fair and reliable test. Explain clearly what they should do.

• Explain what the independent, dependent and control variables are
• Explain what makes a test fair
• Explain how repeats and a mean make results more reliable
• Explain what an anomalous result is and what to do about it
• Explain how to draw a conclusion from the results