KS3 Science Study Pack: Scientific Investigation

Key Knowledge

Scientific investigation is the part of science where you plan tests, collect evidence, analyse results, and decide what the evidence shows. Scientists do not just say what they think. They use careful methods and measurements so that their conclusions are supported by data.

A good investigation usually begins with a testable question. A testable question is one that can be answered by collecting evidence. For example, "How does temperature affect the time taken for sugar to dissolve?" is testable because temperature can be changed and dissolving time can be measured. "Is sugar interesting?" is not a useful scientific investigation question because it depends on opinion.

In KS3, scientific investigation is about thinking clearly:

• What am I changing?
• What am I measuring?
• What must I keep the same?
• How will I measure safely and accurately?
• How will I record the results?
• What pattern do the results show?
• How confident can I be in my conclusion?

The most important idea is evidence. A conclusion should be based on results, not on what a student hoped would happen.

What Is a Scientific Investigation?

A scientific investigation is a planned way of answering a question using evidence. It should be organised enough that another student could repeat it and compare their results.

Most school investigations include these stages:

1. Ask a testable question.
2. Make a prediction or hypothesis.
3. Identify the variables.
4. Plan a fair and safe method.
5. Choose suitable equipment and units.
6. Collect repeat results.
7. Record raw data in a table.
8. Calculate means where useful.
9. Draw a graph or chart if appropriate.
10. Write a conclusion using evidence.
11. Evaluate the method and suggest improvements.

A scientific investigation is not just "doing a practical". The practical activity only becomes a scientific investigation when it is linked to a clear question, controlled variables, careful measurements, and evidence-based conclusions.

Scientific Questions, Hypotheses, and Predictions

A scientific question should be clear and testable. It often has this structure:

• How does [independent variable] affect [dependent variable]?
• What is the effect of [independent variable] on [dependent variable]?
• Which [category] produces the greatest [measurement]?

Examples:

• How does the height of a ramp affect the distance a toy car travels?
• How does temperature affect the time taken for sugar to dissolve?
• How does wire length affect resistance in a simple circuit?
• Which surface needs the greatest force to pull a block across it?

A hypothesis is a scientific idea that can be tested. A prediction says what you expect to happen, usually using "if... then... because..." structure.

A prediction is not just a guess. It should include a scientific reason.

Weak prediction:

• I think the car will go further because it just will.

Better prediction:

• If the ramp height increases, then the toy car will travel a greater distance because it has more gravitational energy at the start, so it can gain more speed as it rolls down the ramp.

Useful prediction sentence stems:

Sentence starter	Example
If the independent variable increases, then...	If the water temperature increases, then the sugar will dissolve faster.
This is because...	This is because particles move faster at higher temperatures.
I predict this pattern because...	I predict this pattern because a steeper ramp gives the car more energy.

Variables and Fair Testing

Variables are factors that can change in an investigation. Knowing the variables helps you plan a fair test.

Type of variable	Meaning	Memory clue	Example for toy car ramp
Independent variable	The variable changed by the investigator	I change it	Ramp height
Dependent variable	The variable measured or observed	Depends on what I change	Distance travelled
Control variables	Variables kept the same	Control means keep constant	Same car, same ramp surface, same start position, same floor surface

A fair test changes only one independent variable and keeps important control variables the same. This does not mean everything stays the same. The independent variable must change, otherwise there is nothing to test.

Worked Example: Identifying Variables

Investigation question:

"How does the height of a ramp affect the distance a toy car travels?"

Step-by-step thinking:

1. What is deliberately changed?

   • The height of the ramp.
   • Independent variable = ramp height.

2. What is measured?

   • The distance the toy car travels after leaving the ramp.
   • Dependent variable = distance travelled.

3. What must be kept the same to make it fair?

   • Same toy car.
   • Same ramp surface.
   • Same starting position.
   • Same way of releasing the car.
   • Same floor surface.
   • Same ruler or tape measure method.

If a student changed the ramp height and also used a different car each time, the test would not be fair. The distance might change because of the car, not because of the ramp height.

Variables Table for Different Investigations

Investigation question	Independent variable	Dependent variable	Important control variables
How does ramp height affect distance travelled by a toy car?	Ramp height in cm	Distance travelled in cm	Same car, ramp, start line, floor surface, release method
How does temperature affect the time taken for sugar to dissolve?	Water temperature in degrees C	Time taken to dissolve in s	Same mass of sugar, same volume of water, same stirring method, same beaker
How does the number of elastic bands affect launch distance?	Number of elastic bands	Launch distance in cm or m	Same launcher, same object, same launch angle, same pull-back distance if not the independent variable
How does light intensity affect pondweed bubble rate?	Light intensity or lamp distance	Number of bubbles per minute	Same pondweed length, same water temperature, same time period, same lamp type
How does surface type affect friction?	Surface type	Force needed to pull block in N	Same block, same mass on block, same pulling speed, same force meter
How does wire length affect resistance?	Wire length in cm	Resistance in ohms or current/voltage readings	Same wire material, same thickness, same power supply voltage, same temperature

Planning a Safe Method

A method is a numbered set of instructions explaining exactly how to carry out an investigation. It should include enough detail for another student to repeat it.

A strong method includes:

• equipment names,
• exact values or ranges,
• the independent variable values,
• how the dependent variable is measured,
• control variables,
• repeats,
• safety precautions,
• how results will be recorded.

Weak Method

"Put a car on a ramp and see how far it goes. Change the ramp and do it again."

This is weak because it does not say:

• how high the ramp is,
• where the car starts,
• how distance is measured,
• how many repeats are done,
• which variables are controlled,
• how to release the car,
• what safety steps are needed.

Improved Method: Toy Car Ramp

1. Set up a ramp using a wooden board and a stack of books.
2. Place the bottom of the ramp at the start line on the floor.
3. Set the ramp height to 10 cm, measuring vertically from the floor to the top of the ramp.
4. Place the same toy car at the marked start position on the ramp.
5. Release the car without pushing it.
6. Measure the distance travelled from the start line to the front of the car using a tape measure.
7. Record the distance in cm in a results table.
8. Repeat the test three times at 10 cm.
9. Repeat steps 3 to 8 for ramp heights of 20 cm, 30 cm, 40 cm, and 50 cm.
10. Keep the same car, ramp surface, floor surface, start position, and release method throughout.
11. Keep bags and feet away from the track so nobody trips.
12. Calculate the mean distance for each ramp height.

This method is repeatable because it gives enough detail for another student to use the same method.

Fair-Test Planning Table

Investigation question	Variables	Control measures	Safety notes
How does ramp height affect distance travelled?	Change ramp height; measure distance	Use same car, ramp, start line, floor, release method	Keep walkway clear; do not run after car
How does temperature affect sugar dissolving time?	Change water temperature; measure dissolving time	Same sugar mass, water volume, beaker, stirring method	Use warm water carefully; teacher handles hot water if needed
How does surface affect friction?	Change surface; measure force	Same block, same mass, pull at steady speed	Pull gently; keep force meter away from faces
How does light intensity affect pondweed bubbles?	Change lamp distance; count bubbles	Same pondweed, time period, water conditions	Keep electrical equipment away from water; avoid overheating

Risk assessment is part of planning. A hazard is something that could cause harm, such as hot water or glassware. A risk is the chance of harm happening. A control measure is something you do to reduce the risk.

Example:

Hazard	Risk	Control measure
Hot water	Burns or scalds	Use warm, not boiling, water; carry carefully; teacher supervises
Glass beaker	Broken glass cuts skin	Keep beaker away from table edge; report breakages
Moving toy car	Trip hazard or collision	Keep track area clear; do not place face near track

Choosing Equipment and Units

Good equipment choices make results more accurate, precise, and useful. You should choose equipment that measures the dependent variable clearly and has a suitable resolution.

Resolution means the smallest change an instrument can measure. A ruler marked in millimetres has a resolution of 1 mm. A balance that reads to 0.1 g has a resolution of 0.1 g.

Instrument	Quantity measured	Common unit	Example resolution
Ruler	Length or distance	mm, cm, m	1 mm
Tape measure	Longer distance	cm, m	1 mm or 1 cm
Stopwatch	Time	s	0.01 s or 1 s
Thermometer	Temperature	degrees C	1 degree C or 0.1 degrees C
Measuring cylinder	Volume	cm3 or ml	1 ml
Balance	Mass	g	0.1 g or 1 g
Force meter	Force	N	0.1 N or 1 N
Light meter	Light intensity	lux	depends on meter
Voltmeter	Potential difference	V	0.1 V or 0.01 V
Data logger	Different quantities using sensors	depends on sensor	depends on sensor

Units should appear in table headings, not repeated in every cell. For example, write "Time taken (s)" as the heading, then write 42, 39, and 41 in the cells.

Results Tables and Data Collection

Raw data means the original measurements collected during the investigation. Results should be recorded clearly and honestly, even if they do not fit the expected pattern.

A good results table has:

• a clear title,
• the independent variable in the first column,
• repeat readings in separate columns,
• a mean column if repeats are used,
• units in headings,
• consistent decimal places,
• rows in a sensible order.

Results Table Layout

Results for: How does ramp height affect distance travelled?

+------------------+--------------+--------------+--------------+-----------+
| Ramp height (cm) | Repeat 1 (cm)| Repeat 2 (cm)| Repeat 3 (cm)| Mean (cm) |
+------------------+--------------+--------------+--------------+-----------+
| 10               |              |              |              |           |
| 20               |              |              |              |           |
| 30               |              |              |              |           |
+------------------+--------------+--------------+--------------+-----------+

Units are in the headings, not repeated in every data cell.

Results Table Template

Independent variable and unit	Repeat 1 and unit	Repeat 2 and unit	Repeat 3 and unit	Mean and unit
Value 1
Value 2
Value 3

Repeats, Means, and Anomalies

Repeats are repeated measurements taken using the same method. They help scientists see whether results are consistent. Repeats can help improve reliability, but they do not automatically make results accurate. If the method is poor, repeated results can still be wrong.

The mean is an average. To calculate a mean:

1. Add the repeat results.
2. Divide by the number of results used.
3. Give the answer with a suitable unit.

Example:

Three distances are 22 cm, 24 cm, and 23 cm.

Mean = (22 + 24 + 23) / 3 = 69 / 3 = 23 cm.

An anomaly is a result that does not fit the pattern. Scientists should not delete anomalies just because they are inconvenient. They should first check for possible causes, repeat the measurement if possible, and only exclude the anomaly if there is a clear reason.

Example:

For a ramp height of 30 cm, the distances are 78 cm, 80 cm, and 29 cm. The 29 cm result is likely to be anomalous because it is very different from the other repeats and does not fit the pattern. The sensible action is to repeat that reading. If the car hit an obstacle during the 29 cm trial, that is a clear reason to exclude it.

Accuracy, Precision, Reliability, and Repeatability

These words are often confused, but they have different meanings.

Term	Meaning	Simple example
Accuracy	How close a measurement is to the true value	A thermometer reads 20 degrees C when the water is actually 20 degrees C
Precision	How close repeated measurements are to each other, or how finely an instrument measures	Three results of 21.1 cm, 21.2 cm, and 21.1 cm are precise
Resolution	The smallest change an instrument can measure	A ruler marked in mm has 1 mm resolution
Reliability	Whether results are trustworthy because the method is suitable and repeated results are consistent	Similar repeat results from a fair method are more reliable
Repeatability	Whether the same person can repeat the same method and get similar results	You repeat the ramp test and get similar distances
Reproducibility	Whether another person or group can use the method and get similar results	Another group follows your method and gets a similar pattern
Validity	Whether the investigation actually tests the question it claims to test	A ramp investigation is more valid if only ramp height is changed

Repeatability Comparison Diagram

Close repeated results: more precise and repeatable

Trial 1: 24 cm
Trial 2: 25 cm
Trial 3: 24 cm

Scattered repeated results: less precise and less repeatable

Trial 1: 18 cm
Trial 2: 31 cm
Trial 3: 24 cm

Important: precise results are not always accurate. A stopwatch could be started late every time. The repeated times might be close together, but all of them could be too short.

Drawing and Interpreting Graphs

Graphs help scientists see patterns. The graph type depends on the independent variable.

Graph or display	When to use it	Example
Line graph	The independent variable is continuous numerical data	Temperature and dissolving time
Bar chart	The independent variable is a category	Surface type and friction force
Results table only	You have only a few values or no clear graph is needed	Safety observations
Diagram	You need to show equipment setup or a process	Ramp setup diagram

Continuous variables can take many values on a scale, such as temperature, time, length, mass, or voltage. Categories are groups or names, such as surface type, material, or brand.

A good graph has:

• a title,
• independent variable on the x-axis,
• dependent variable on the y-axis,
• axis labels with units,
• sensible scale,
• accurately plotted points,
• a best-fit line or curve where suitable.

A best-fit line does not need to join every point. It shows the overall trend.

Line Graph Layout

Time taken for sugar to dissolve (s)
90 | *
80 |
70 |     *
60 |
50 |          *
40 |
30 |               *
20 |                    *
10 |
 0 +----+----+----+----+---- Temperature (degrees C)
    20   30   40   50   60

x-axis: independent variable
y-axis: dependent variable
Pattern: as temperature increases, dissolving time decreases.

Anomaly on a Simple Graph

Distance travelled (cm)
120 |                       *
100 |                  *
 80 |             *
 60 |        *
 40 |     x        <- possible anomaly
 20 |  *
  0 +----+----+----+----+---- Ramp height (cm)
     10   20   30   40   50

The point marked x does not fit the overall increasing trend.
It should be checked and repeated if possible.

To describe a trend, use a sentence like:

"As the independent variable increases, the dependent variable..."

Then add evidence:

"For example, when the temperature increased from 20 degrees C to 60 degrees C, the dissolving time decreased from 85 s to 22 s."

Writing Conclusions From Evidence

A conclusion answers the original question using evidence from the results. It should not be based on expectations, guesses, or what "should" happen.

A strong conclusion includes:

• an answer to the question,
• the pattern or relationship,
• numerical evidence,
• scientific explanation if possible,
• mention of anomalies or limits if relevant.

Conclusion structure:

1. "The results show that..."
2. "This is supported by..."
3. "This may be because..."
4. "However, one limitation is..."

Weak conclusion:

"The ramp made the car go further. It worked."

Better conclusion:

"The results show that increasing the ramp height increased the distance travelled by the toy car. For example, at 10 cm the mean distance was 42 cm, but at 50 cm the mean distance was 132 cm. This may be because a higher ramp gives the car more gravitational energy, which is transferred to kinetic energy as it rolls down. One result at 30 cm was anomalous, so that reading should be repeated before the conclusion is fully reliable."

Evaluating and Improving Investigations

Evaluation means judging the quality of the investigation. It is not enough to write "human error". You must explain the specific problem and how it affected the results.

Good evaluation answers include:

• one strength of the method,
• one weakness or limitation,
• how the weakness may affect results,
• a specific improvement.

Evaluation focus	Weak answer	Better answer
Timing	Human error	Reaction time when starting and stopping the stopwatch may have made dissolving times less precise
Measuring distance	The ruler was bad	The tape measure may not have been straight, so distance readings could be inaccurate
Control variables	It was not fair	The water volume was not kept the same, so dissolving time may have changed because of volume rather than temperature
Improvement	Be more careful	Use the same measured volume of water each time and stir at a fixed rate

Evaluation Sentence Starters

Purpose	Sentence starter
Strength	One strength of the method was...
Weakness	One weakness of the method was...
Effect on results	This could have affected the results because...
Reliability	The reliability could be improved by...
Accuracy	The accuracy could be improved by...
Control variable	To make the test fairer, I would keep... the same by...
Anomaly	The anomalous result should be checked by...

Worked Investigation: Dissolving Sugar

Question:

How does water temperature affect the time taken for sugar to dissolve?

Prediction:

If the water temperature increases, then the sugar will dissolve faster, so the time taken will decrease. This is because particles in warmer water move faster and collide with the sugar more often, helping the sugar particles spread through the water.

Variables:

Variable type	Variable
Independent variable	Water temperature in degrees C
Dependent variable	Time taken for sugar to dissolve in seconds
Control variables	Mass of sugar, volume of water, beaker size, stirring method, type of sugar

Equipment:

• beaker,
• measuring cylinder,
• thermometer,
• balance,
• stopwatch,
• sugar,
• water at different temperatures,
• stirring rod.

Safe method:

1. Measure 100 ml of water into a beaker.
2. Use a thermometer to check the water temperature is 20 degrees C.
3. Measure 5.0 g of sugar using a balance.
4. Add the sugar to the water and start the stopwatch.
5. Stir using the same method, for example one full stir every second.
6. Stop the stopwatch when no sugar crystals can be seen.
7. Record the time in seconds.
8. Repeat three times at 20 degrees C.
9. Repeat for 30 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C.
10. Use warm water carefully and follow the teacher's safety instructions.

Dissolving Investigation Setup

             Thermometer
                 |
                 v
           ______________
          /              \
         /   water +      \       Stopwatch
        |    sugar         |      [00:00]
        |                  |
         \________________/
              Beaker

Sugar mass = 5.0 g each time
Water volume = 100 ml each time
Stirring method = one stir per second
Temperature = independent variable
Time to dissolve = dependent variable

Example results:

Temperature (degrees C)	Repeat 1 (s)	Repeat 2 (s)	Repeat 3 (s)	Mean (s)
20	85	87	83	85
30	68	66	67	67
40	49	51	50	50
50	34	35	33	34
60	22	23	21	22

Conclusion:

The results show that increasing the temperature decreases the time taken for sugar to dissolve. At 20 degrees C, the mean dissolving time was 85 s, but at 60 degrees C it was 22 s. This supports the prediction that warmer water dissolves sugar faster. The results are reliable because the repeats are close together, but the method could be improved by using a mechanical stirrer so that stirring speed is exactly the same each time.

Worked Investigation: Stretching a Spring

Question:

How does the force on a spring affect the extension of the spring?

Prediction:

If the force increases, then the extension of the spring will increase because a larger force stretches the spring more.

Variables:

Variable type	Variable
Independent variable	Force added to the spring in newtons
Dependent variable	Extension of the spring in cm
Control variables	Same spring, same ruler position, same starting length, same place where length is measured

Method:

1. Hang a spring from a clamp stand.
2. Place a ruler beside the spring.
3. Measure the spring's original length before adding masses.
4. Add a 1 N weight and measure the new length.
5. Calculate extension by subtracting the original length from the new length.
6. Repeat for 2 N, 3 N, 4 N, and 5 N.
7. Do not overload the spring.
8. Wear eye protection if instructed and keep feet clear of falling masses.

Example results:

Force (N)	Length (cm)	Extension (cm)
0	8.0	0.0
1	10.1	2.1
2	12.0	4.0
3	14.2	6.2
4	16.1	8.1
5	18.0	10.0

Pattern:

As force increases, extension increases. The data show an approximately steady increase of about 2 cm for each extra newton.

Evaluation:

The ruler must be placed carefully at the same height each time. If the ruler moves, the readings may be inaccurate. The investigation could be improved by using a pointer attached to the spring to make the scale easier to read.

Real-World Examples

Scientific investigation skills are used outside school.

• Sports scientists test how training affects running speed, but they must control factors such as footwear, distance, rest time, and weather.
• Doctors test medicines using evidence, repeat results, and careful controls.
• Environmental scientists measure river pollution and compare results over time.
• Engineers test materials to see which are strongest or most flexible.
• Food scientists test recipes by changing one ingredient at a time.
• Product designers test how surface type affects friction, grip, and safety.

The same basic ideas appear again and again: change one thing, measure carefully, control important factors, repeat results, and use evidence.

Ethical and environmental care also matters. Scientists should use small quantities where possible, avoid waste, dispose of materials safely, and treat living things responsibly. Pondweed investigations should use living material carefully and return or dispose of it according to school guidance.

Key Vocabulary

Term	Definition	Example
Scientific investigation	A planned way to answer a question using evidence	Testing how temperature affects dissolving
Evidence	Data or observations used to support a conclusion	Mean distances from a ramp test
Testable question	A question that can be answered by collecting measurements or observations	How does surface type affect friction?
Hypothesis	A scientific idea that can be tested	Warmer water makes sugar dissolve faster
Prediction	A statement saying what you expect and why	If temperature increases, dissolving time decreases because particles move faster
Independent variable	The variable changed by the investigator	Ramp height
Dependent variable	The variable measured	Distance travelled
Control variable	A variable kept the same	Same toy car
Fair test	A test where only the independent variable is changed and important controls are kept constant	Changing only ramp height
Hazard	Something that could cause harm	Hot water
Risk	The chance that harm may happen	Scalding from hot water
Control measure	An action that reduces risk	Use warm water carefully
Accuracy	How close a measurement is to the true value	A balance correctly reads 5.0 g
Precision	How close repeated results are to each other, or how finely equipment measures	10.1 cm, 10.2 cm, 10.1 cm
Resolution	The smallest change an instrument can measure	1 mm on a ruler
Reliability	How trustworthy results are	Repeats are consistent and method is suitable
Repeatability	Same person repeats method and gets similar results	Your second ramp test gives a similar pattern
Reproducibility	Another person or group gets similar results using the method	Another group also finds higher ramps give longer distances
Validity	Whether the investigation tests what it is meant to test	A friction test is valid if only surface type changes
Raw data	Original measurements recorded during the investigation	Stopwatch readings before calculating means
Mean	An average found by adding values and dividing by how many values there are	(22 + 24 + 23) / 3 = 23
Anomaly	A result that does not fit the pattern	29 cm when other repeats are 78 cm and 80 cm
Continuous variable	A variable measured on a scale	Temperature
Category	A group or type	Carpet, wood, rubber
Line graph	A graph used for continuous independent variables	Temperature against dissolving time
Bar chart	A chart used for categories	Surface type against force
Best-fit line	A line showing the overall trend	A line through the middle of plotted points
Conclusion	An answer to the question using evidence	Higher ramps increased mean distance
Evaluation	A judgement of method quality and improvements	Use a light gate instead of a stopwatch

Common Misconceptions

Misconception	Correction
Repeating an experiment automatically makes results accurate.	Repeats can improve reliability and help spot anomalies, but accuracy depends on the method and equipment.
Accuracy and precision mean the same thing.	Accuracy means close to the true value. Precision means repeated results are close together or equipment measures in small steps.
The independent variable is the result.	The independent variable is changed by the investigator. The dependent variable is the result that is measured.
Control variables are changed carefully.	Control variables are kept the same.
A fair test means everything is kept the same.	The independent variable must change. Other important variables are kept the same.
A prediction is just a guess.	A scientific prediction includes a reason.
An anomaly should always be deleted.	Anomalies should be investigated and repeated if possible. Only exclude one with a clear reason.
A line graph is always better than a bar chart.	Graph choice depends on the independent variable. Use bar charts for categories and line graphs for continuous variables.
A best-fit line must join every point.	A best-fit line shows the overall trend and does not have to touch every point.
More decimal places always mean better data.	Decimal places should match the resolution of the measuring instrument.
Reliability and repeatability are identical.	Repeatability is one way to support reliability, but reliability also depends on the method being suitable.
A conclusion can be based on what students expected.	A conclusion must be based on evidence from results.
"Human error" is a complete evaluation.	A good evaluation names the specific problem, such as reaction time when using a stopwatch.

Diagram and Data Interpretation Practice

Task 1: Toy Car Ramp Setup

             Toy car
                |
                v
           [ car ]
             ___
            /  /|
           /__/ | ramp
          /__/  |
         /__/   |
 start line |____________________________________ floor
            <-------------- distance travelled -------------->
                         ruler or tape measure

Ramp height = independent variable
Distance travelled = dependent variable
Same car, ramp and floor = control variables

Questions:

1. What is the independent variable?
2. What is the dependent variable?
3. Name two control variables.
4. Why should the car be released without pushing?
5. What safety rule would help prevent accidents?

Model answers:

1. Ramp height.
2. Distance travelled.
3. Same car and same ramp surface. Other correct answers include same start line, same floor, or same release method.
4. Pushing the car would add an extra force and make the test unfair.
5. Keep the track area clear so nobody trips or steps on the car.

Task 2: Ramp Height Results With an Anomaly

Ramp height (cm)	Repeat 1 (cm)	Repeat 2 (cm)	Repeat 3 (cm)	Mean (cm)
10	42	44	43	43
20	61	63	62	62
30	79	28	81	80 if anomaly excluded
40	105	108	106	106
50	132	134	130	132

Questions:

1. Which result is anomalous?
2. Why does it look anomalous?
3. What should the student do before deciding whether to exclude it?
4. Describe the overall pattern.
5. Use evidence to support the pattern.

Model answers:

1. 28 cm at 30 cm ramp height.
2. It is much lower than the other repeats at 30 cm, which are 79 cm and 81 cm, and it does not fit the increasing trend.
3. Repeat the 30 cm test and check whether something went wrong, such as the car hitting an obstacle.
4. As ramp height increases, distance travelled increases.
5. At 10 cm the mean distance was 43 cm, but at 50 cm it was 132 cm.

Task 3: Line Graph Interpretation

Stimulus data:

Temperature (degrees C)	Mean dissolving time (s)
20	85
30	67
40	50
50	34
60	22

Questions:

1. Which variable goes on the x-axis?
2. Which variable goes on the y-axis?
3. Describe the trend.
4. Support the trend with two values.
5. Suggest one reason for the trend.

Model answers:

1. Temperature goes on the x-axis because it is the independent variable.
2. Mean dissolving time goes on the y-axis because it is the dependent variable.
3. As temperature increases, dissolving time decreases.
4. At 20 degrees C the mean time was 85 s, while at 60 degrees C it was 22 s.
5. Particles move faster in warmer water, so the sugar dissolves more quickly.

Task 4: Bar Chart Data for Friction

A student pulls the same block across different surfaces using a force meter.

Surface	Mean force needed (N)
Smooth wood	1.2
Plastic	1.5
Carpet	3.8
Rubber mat	4.6

Questions:

1. Why is a bar chart suitable for this data?
2. Which surface produced the greatest friction?
3. Give evidence for your answer.
4. Name one control variable.
5. Suggest one improvement to make the results more reliable.

Model answers:

1. Surface type is a category, so a bar chart is suitable.
2. Rubber mat.
3. It needed the highest mean force, 4.6 N.
4. Same block, same mass on the block, same pulling speed, or same force meter.
5. Repeat each surface test at least three times and calculate a mean.

Task 5: Method Evaluation

A student writes:

"I will test how temperature affects dissolving. I will use different amounts of sugar and different temperatures of water. I will time how long it takes."

Questions:

1. What is the main control variable problem?
2. Why does this make the test unfair?
3. Rewrite one improved control measure.
4. Name one piece of equipment needed to measure temperature.

Model answers:

1. The amount of sugar is changing as well as the temperature.
2. The dissolving time might change because of sugar mass, not because of temperature.
3. Use exactly 5.0 g of sugar each time, measured with a balance.
4. A thermometer.

Task 6: Table Completion

Complete the missing means and identify the result that should be repeated.

Water volume (ml)	Repeat 1 time (s)	Repeat 2 time (s)	Repeat 3 time (s)	Mean time (s)
50	31	33	32	32
100	46	44	45	45
150	62	95	63	?

Questions:

1. Calculate the mean for 150 ml using all three repeats.
2. Which result may need repeating?
3. Why?
4. What unit should be in the mean heading?

Model answers:

1. (62 + 95 + 63) / 3 = 220 / 3 = 73.3 s.
2. 95 s.
3. It is much higher than 62 s and 63 s, so it may be anomalous.
4. Seconds, shown as s.

If there is a clear reason to exclude 95 s, such as the student forgot to stir, the mean from the two sensible repeats would be (62 + 63) / 2 = 62.5 s. The student should repeat the test before making that decision if possible.

Task 7: Graph Choice

Dataset	Best display	Reason
Temperature and dissolving time	Line graph	Temperature is continuous
Surface type and friction force	Bar chart	Surface type is categorical
Labelled equipment setup	Diagram	Shows positions of apparatus
A few safety hazards and control measures	Table	Organises written information
Wire length and resistance	Line graph	Wire length is continuous
Type of material and whether it floats	Bar chart or table	Material type is categorical

Task 8: Conclusion Writing

Data:

Number of elastic bands	Mean launch distance (cm)
1	35
2	58
3	81
4	98

Write a conclusion using evidence.

Model answer:

The results show that increasing the number of elastic bands increased the mean launch distance. With 1 elastic band, the mean distance was 35 cm, but with 4 elastic bands it increased to 98 cm. This suggests that using more elastic bands stores more elastic energy, which can transfer more energy to the launched object. The conclusion would be more reliable if each test was repeated and any anomalies were checked.

Exam-Style Questions With Model Answers

Multiple-Choice Questions

1. Which statement best describes the independent variable?

A. The variable measured at the end
B. The variable changed by the investigator
C. The variable kept the same
D. The variable that is always inaccurate

Answer: B.

2. A student investigates how surface type affects friction. Which graph should usually be used?

A. Line graph
B. Bar chart
C. Pie chart
D. No table or graph

Answer: B, because surface type is a category.

3. Which statement about repeats is correct?

A. Repeats always make results accurate.
B. Repeats can help spot anomalies and improve reliability.
C. Repeats mean control variables are unnecessary.
D. Repeats should only be done when results are perfect.

Answer: B.

4. Which is the best evaluation?

A. There was human error.
B. It went wrong.
C. Reaction time when stopping the stopwatch may have made the time less precise.
D. The results were bad.

Answer: C.

5. Which instrument is most suitable for measuring force?

A. Thermometer
B. Measuring cylinder
C. Force meter
D. Stopwatch

Answer: C.

Fill-in-the-Blank Questions

Complete the sentences using these words: independent, dependent, control, anomaly, mean, fair.

1. The variable changed by the investigator is the __________ variable.
2. The variable measured is the __________ variable.
3. Variables kept the same are __________ variables.
4. A result that does not fit the pattern is an __________.
5. A test where only one important variable is changed is a __________ test.
6. A __________ is calculated by adding values and dividing by how many values there are.

Answers:

1. independent
2. dependent
3. control
4. anomaly
5. fair
6. mean

Short-Answer Questions

1. Explain the difference between accuracy and precision.

Model answer:

Accuracy is how close a measurement is to the true value. Precision is how close repeated measurements are to each other, or how finely an instrument measures. For example, three readings might be precise because they are close together, but inaccurate if the equipment is not correctly calibrated.

2. Why should units be written in table headings?

Model answer:

Units in headings make the table clear and avoid repeating units in every data cell. For example, "Time (s)" shows that all values in that column are measured in seconds.

3. A student says, "The best-fit line must join all the points." Explain why this is wrong.

Model answer:

A best-fit line shows the overall trend. It does not have to pass through every point because real results may vary slightly and some points may be anomalous.

4. Why is "I think it will happen because I think so" not a good prediction?

Model answer:

A scientific prediction needs a reason linked to science. It should explain why the pattern is expected.

Table-Completion Question

A student investigates how wire length affects current in a simple circuit.

Wire length (cm)	Repeat 1 current (A)	Repeat 2 current (A)	Repeat 3 current (A)	Mean current (A)
10	0.80	0.82	0.81	?
20	0.61	0.60	0.62	?
30	0.49	0.30	0.48	?

Questions:

1. Calculate the mean current for 10 cm.
2. Calculate the mean current for 20 cm.
3. Identify a possible anomaly.
4. Name one control variable.

Model answers:

1. (0.80 + 0.82 + 0.81) / 3 = 0.81 A.
2. (0.61 + 0.60 + 0.62) / 3 = 0.61 A.
3. 0.30 A at 30 cm, because it is much lower than 0.49 A and 0.48 A.
4. Same wire material, same wire thickness, same power supply voltage, or same circuit equipment.

Graph Interpretation Question

A class investigates how distance from a lamp affects the number of pondweed bubbles produced per minute.

Distance from lamp (cm)	Bubbles per minute
10	42
20	31
30	23
40	15
50	10

Questions:

1. What is the independent variable?
2. What is the dependent variable?
3. Describe the trend.
4. Use data to support your answer.
5. Suggest one control variable.
6. Suggest one limitation of counting bubbles.

Model answers:

1. Distance from the lamp.
2. Number of bubbles per minute.
3. As distance from the lamp increases, the number of bubbles per minute decreases.
4. At 10 cm there were 42 bubbles per minute, but at 50 cm there were 10 bubbles per minute.
5. Same pondweed length, same lamp, same water temperature, same time period, or same species of pondweed.
6. Bubble size may vary, so counting bubbles is only an approximate measure of photosynthesis rate.

Method-Writing Question

A student wants to investigate how different surfaces affect the force needed to pull a block.

Write a method.

Model answer:

1. Attach a force meter to the same wooden block.
2. Place the block on the first surface, such as smooth wood.
3. Pull the block steadily using the force meter.
4. Record the force needed to keep the block moving at a steady speed in newtons.
5. Repeat three times on the same surface and calculate a mean.
6. Repeat for other surfaces, such as plastic, carpet, and rubber mat.
7. Keep the same block, same mass on the block, same force meter, and same pulling speed.
8. Pull gently and keep the force meter away from faces.

Evaluation Question

A student tests dissolving time but uses "a spoonful" of sugar each time.

Explain why this is a weakness and suggest an improvement.

Model answer:

Using "a spoonful" is a weakness because the mass of sugar may be different each time. This makes the test unfair because dissolving time could change because of sugar mass rather than temperature. The improvement is to measure the same mass of sugar each time, for example 5.0 g, using a balance.

Longer 8-Mark Question

A student wants to investigate how the height of a ramp affects the distance a toy car travels. Write a method for the investigation. Include the variables, how to make it a fair test, how to collect reliable results, and one way to improve the method.

Model answer:

The independent variable is the height of the ramp, measured in cm. The dependent variable is the distance travelled by the toy car, measured in cm. Control variables include using the same toy car, same ramp, same start position, same floor surface, and same release method.

To carry out the investigation, set up a ramp using a board and books. Measure the ramp height as 10 cm using a ruler. Place the car at a marked start line and release it without pushing. Measure the distance from the bottom start line to where the front of the car stops using a tape measure. Record the result in a table. Repeat the test three times at 10 cm and calculate a mean. Repeat the method for 20 cm, 30 cm, 40 cm, and 50 cm. Keep the track area clear for safety.

The test is fair because only the ramp height changes while important control variables are kept the same. Reliable results are collected by doing repeats, checking for anomalies, and calculating means. One improvement would be to use a release gate so the car is released in exactly the same way each time.

Revision Checklist

Use this checklist to check your understanding.

I can...	Confident	Need more practice
Explain the purpose of a scientific investigation
Write a testable scientific question
Write a prediction using "if... then... because..."
Identify independent, dependent, and control variables
Explain what makes a test fair
Write a safe method in numbered steps
Choose suitable equipment and units
Explain hazards, risks, and control measures
Draw a results table with units in headings
Calculate a mean average
Identify an anomaly and explain what to do about it
Explain accuracy, precision, resolution, reliability, and repeatability
Choose between a line graph and a bar chart
Label graph axes with variables and units
Describe a trend using evidence
Write a conclusion based on results
Evaluate a method with specific improvements
Explain why repeats do not automatically make results accurate
Use scientific vocabulary correctly

Quick Revision Summary

Scientific investigations answer testable questions using evidence. The independent variable is changed, the dependent variable is measured, and control variables are kept the same. A fair test changes only the independent variable while controlling other important factors.

Good methods are safe, detailed, and repeatable. Results should be recorded honestly in clear tables with units in headings. Repeats help improve reliability and spot anomalies, but accuracy depends on using suitable equipment and a good method.

Line graphs are used for continuous independent variables, such as temperature or length. Bar charts are used for categories, such as surface type. Conclusions must answer the question and use numerical evidence. Evaluations should name specific weaknesses and suggest specific improvements.