Year 7 Science · Unit 2 · Lesson 11
Foundation Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. The dependent variable is the one thing you change in a fair test.
Correct it:
2. Repeating trials three times and averaging the results makes an experiment valid.
Correct it:
3. In a fair test, you change only one variable at a time.
Correct it:
4. Results can be reliable but not valid, for example when scales that read 10 g too heavy give the same wrong mass every time.
Correct it:
Match each term to its definition
Write the letter of the correct definition next to each term. Each letter is used once.
| Term | Letter | Definition |
|---|---|---|
| Independent variable | A. Measuring what you actually intend to measure, with only one variable changed | |
| Dependent variable | B. Something kept the same throughout the experiment | |
| Controlled variable | C. Getting similar results each time you repeat the experiment | |
| Reliability | D. A testable prediction written as “If … then … because …” | |
| Validity | E. The one thing you deliberately change in a fair test | |
| Hypothesis | F. What you measure: the result, which depends on what you changed |
Plan the investigation: stirring instant coffee
Mia’s question: Does the number of stirs per minute affect how long 5 g of instant coffee takes to dissolve in 150 mL of cold water? Her equipment: coffee granules, a balance, cups, a measuring cylinder and a stopwatch. Plan her fair test.
Hypothesis
If the number of stirs per minute increases, then … because …
Variables
Method
Give amounts, when to start and stop timing, and how many repeats.
Results table: write the column headings, with units
Read the data: Mia’s results
Mia’s results
Mia tested four stirring rates, with three trials at each rate. She stopped the stopwatch when no coffee granules could be seen.
| Stirs per minute | Trial 1 (s) | Trial 2 (s) | Trial 3 (s) | Average (s) |
|---|---|---|---|---|
| 0 | 95 | 97 | 96 | 96 |
| 20 | 61 | 59 | 60 | 60 |
| 40 | 38 | 54 | 38 | |
| 60 | 26 | 24 | 25 | 25 |
Source: sample class results for this worksheet.
1. Work out the average time for 40 stirs per minute, to the nearest second. Write it in Table 1.
Answer s
2. Describe the trend in the averages. Does it support the idea that more stirring makes coffee dissolve faster? Use numbers from Table 1.
3. Which stirring rate has the least reliable results? Explain how you can tell, and say what Mia could do about it.
4. Aisha wants to find out whether salt dissolves faster in tap water or in rainwater. She puts 1 teaspoon of salt in 100 mL of tap water and 2 teaspoons of salt in 250 mL of rainwater, and times each one once. Explain why this is not a fair test, and describe how Aisha should improve it.
True or false
1. False: the independent variable is what you change; the dependent variable is measured. 2. False: repeats and averages make results reliable; validity needs good controls. 3. True. 4. True.
Match each term to its definition
Independent variable → E; Dependent variable → F; Controlled variable → B; Reliability → C; Validity → A; Hypothesis → D.
Plan the investigation: stirring instant coffee
Hypothesis: if the stirs per minute increase, the coffee will dissolve in less time, because stirring brings fresh water to the granules (1). Independent: stirs per minute. Dependent: time to dissolve (s) (1). Controlled, any three: mass of coffee; volume of water; water temperature; type of coffee; same cup (1). Method: e.g. 1. Measure 150 mL of cold water. 2. Add 5 g of coffee; start the stopwatch. 3. Stir at the set rate; stop the watch when no granules are left. 4. Repeat three times at each rate (1 for amounts, timing and repeats). Results table headings: Stirs per minute; Trial 1 (s); Trial 2 (s); Trial 3 (s); Average (s) (1). [5 marks]
Read the data: Mia’s results
1. 130 ÷ 3 (1) = 43 s (1). Accept 38 s if the student leaves out 54 s as not matching the others and says so. [2 marks]
2. More stirs, shorter time: 96 s at 0 stirs falls to 25 s at 60 (1). Yes, it supports the idea (1). [2 marks]
3. 40 stirs per minute: its trials spread from 38 s to 54 s; the other rows differ by only 2 s (1). Mia should repeat that test or do more trials (1). [2 marks]
Question 4
Marking guide: 1 independent variable: type of water; 1 both uncontrolled variables: amount of salt and volume of water; 1 with three things changing she cannot tell which caused a difference, so not valid; 1 same mass of salt, volume, temperature and stirring, only the water type changed; 1 repeat each test at least three times and average. [5 marks]
Model answer: Aisha meant to change only the type of water, but she also changed the amount of salt and the volume, so she cannot tell which made the difference: not valid. She should use 5 g of salt in 100 mL at the same temperature and stirring, changing only the water type, and repeat each test three times and average for reliability.
Common error: thinking repeats make a test fair (they improve reliability).