Science: Working Scientifically and Practical Skills Set 2
Working scientifically and practical skills, set 2, extends Working Scientifically with further practice at planning investigations, writing a prediction supported by scientific reasoning, and evaluating whether a method gives reliable and valid results.
Method
- Before an investigation, write a prediction that states what you expect to happen AND why, linking it to scientific knowledge you already know, rather than just guessing an outcome with no reason given.
- When planning, decide on a sensible range and number of values for the independent variable based on any preliminary (trial) results, so real data is not wasted on values that are too close together or produce results outside the equipment's range.
- When evaluating a method, distinguish between a reliable result (one that would be very similar if repeated) and a valid result (one that is actually measuring what it claims to be measuring, with all other variables properly controlled).
- Identify specific, named sources of error in a described method (for example, parallax error when reading a scale, or heat loss to the surroundings in a temperature experiment), rather than giving a vague answer like 'human error'.
- Suggest one specific improvement for each source of error you identify, explaining how that change would make the result more accurate or more reliable.
- When asked to draw a conclusion, refer to the actual data collected (specific values or the pattern shown), state whether it supports or does not support the original prediction, and avoid claiming more than the data can show.
- For calculations, always check the number of significant figures or decimal places the question asks for, and do not round any values until the final step of the calculation.
Worked example
A pupil predicts that a thicker kitchen roll will absorb more water than a thinner one, because a thicker sheet has more space for water to soak into. She tests three brands of kitchen roll by cutting an identical 10 cm x 10 cm square of each, weighing it dry, dipping it into water for 5 seconds, then weighing it again. Brand: P, Q, R. Thickness (mm): 0.3, 0.5, 0.4. Mass of water absorbed (g): 2.1, 4.8, 3.3. (a) State whether these results support the pupil's prediction. (b) Name one variable that was correctly controlled to make this a fair test.
- Order the brands by thickness: P (0.3 mm) is thinnest, then R (0.4 mm), then Q (0.5 mm) is thickest.
- Order the same brands by mass of water absorbed: P (2.1 g) absorbed least, then R (3.3 g), then Q (4.8 g) absorbed most.
- Compare the two orders: the thickest kitchen roll (Q) absorbed the most water, and the thinnest (P) absorbed the least, so the pattern matches the pupil's prediction.
- For part (b), a correctly controlled variable is the size of each square tested (10 cm x 10 cm for every brand) and the dipping time (5 seconds for every brand), since keeping these the same means thickness is the only variable that differs between the tests.
- Final answer: (a) yes, the results support the prediction, since absorption increased as thickness increased across all three brands. (b) the size of the square and the dipping time were both kept the same (either is a valid answer).
Practice questions
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Q1Before starting a watering investigation, a pupil writes this prediction: a plant given more water each day will grow taller than one given less water. State one piece of scientific reasoning that could support this prediction.Show answer
Answer: Water is needed for photosynthesis and to keep plant cells firm (turgid) so they can grow, so a plant with more available water may be able to grow more, provided all other conditions are the same.
Q2A pupil uses a stopwatch to measure how long a candle takes to burn down by 1 cm, but forgets to shield the candle from a draught in the room. State whether this makes the result less reliable or less valid, and explain your answer.Show answer
Answer: Less valid, because the draught is an uncontrolled variable that could affect the burning rate independently of what is being tested, so the result may not be a fair measure of the candle's normal burning rate.
Q3In an investigation into reaction time, a pupil's results are 0.18 s, 0.19 s, 0.61 s, 0.18 s and 0.20 s. Identify the anomalous result, and suggest one likely reason it occurred.Show answer
Answer: 0.61 s is the anomalous result; a likely reason is the pupil was not concentrating or reacted late on that particular attempt, rather than a genuine change in reaction time.
Q4A pupil wants to find out whether increasing the concentration of a salt solution affects the boiling point of water. Suggest one variable, other than salt concentration, that should be kept the same for this to be a fair test.Show answer
Answer: The volume of water used (or the type of water, or the same thermometer and heat source).
Q5A pupil measures the mass of a metal washer five times using a balance and gets: 14.2 g, 14.5 g, 14.1 g, 14.6 g, 14.1 g. Calculate the mean mass, giving your answer to 3 significant figures.Show answer
Answer: 14.3 g (71.5 / 5 = 14.3).
Q6A pupil's teacher suggests using a data logger to measure temperature every second during an experiment, instead of a pupil reading a thermometer every minute. Suggest one advantage of using a data logger in this experiment.Show answer
Answer: A data logger can take many more readings in a shorter time, and more consistently (without human reaction-time delay or misreading), giving a more detailed and accurate record of how the temperature changes.
Q7A pupil is choosing between two thermometers to measure a temperature change of about 5 degrees C: one has markings every 2 degrees C, and the other has markings every 0.2 degrees C. State which thermometer would give the more precise reading, and explain why.Show answer
Answer: The thermometer with markings every 0.2 degrees C, because its smaller scale divisions (finer resolution) allow the temperature to be read to a more precise value.
Q8A pupil's results table is missing units for one column, headed only 'Volume'. State why it is important to always include a unit in a column heading or with a numerical answer.Show answer
Answer: A number alone does not give a complete measurement; without a unit, 25 could mean 25 cm^3, 25 ml or 25 litres, which are very different amounts, so the unit must be included for the measurement to be meaningful.
Exam-style questions
Written in the style of a 13+ Common Entrance exam paper, with a full mark scheme.
A pupil investigates how drop height affects the bounce height of a tennis ball by dropping it from different heights above a hard floor and judging by eye how high it bounces back up against a metre ruler held next to the drop point. She takes only ONE bounce-height reading at each drop height. (a) Suggest one reason why taking only one reading at each drop height might make her results less reliable. (b) Suggest one source of error in judging the bounce height by eye against a hand-held ruler. (c) State one variable, other than drop height, that she should keep the same across all her tests for the comparison to be a fair test.
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Believing that white light contains all the colours a plant needs for photosynthesis, a pupil expects it to grow seedlings best. She grows identical seedlings under red, green and white light of the same brightness for two weeks and measures the increase in height of each. Light colour: red, green, white. Increase in height (mm): 38, 12, 41. (a) State whether these results support or do not support the pupil's expectation, referring to the data. (b) Suggest a reason why growth under green light was much lower than under red or white light. (c) Name one variable, other than light colour, that the pupil needed to keep the same across all three groups for the comparison to be a fair test.
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Free printable worksheet
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This topic is chapter 16 of 13+ Science Workbook, the whole course as one free printable PDF.
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