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Scientific Enquiry - Planning a fair test

Grade 3IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A Fair Test is a scientific investigation where only one variable is changed, while all other conditions are kept exactly the same.

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The Independent Variable is the one factor that you purposely change to see what happens (e.g., the temperature of H2OH_2O).

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The Dependent Variable is the factor that you measure or observe as a result (e.g., the time in ss it takes for sugar to dissolve).

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Control Variables are all the factors that must stay the same to ensure the test is fair (e.g., using the same amount of liquid, measured in mlml).

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A Prediction is a scientific guess about the outcome of the test, often following the logic: 'If I increase XX, then YY will happen.'

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Reliability is improved by repeating the experiment multiple times and calculating an average result.

📐Formulae

Average (Mean)=Sum of all resultsNumber of trials\text{Average (Mean)} = \frac{\text{Sum of all results}}{\text{Number of trials}}

Distance=Speed×Time\text{Distance} = \text{Speed} \times \text{Time}

Total Change=Final Measurement−Initial Measurement\text{Total Change} = \text{Final Measurement} - \text{Initial Measurement}

💡Examples

Problem 1:

Sarah wants to find out if plants grow taller when given more water. She uses three identical pots with the same soil and the same type of seed. She gives Pot A 10 ml10\ ml of H2OH_2O, Pot B 20 ml20\ ml of H2OH_2O, and Pot C 30 ml30\ ml of H2OH_2O every day. What are the variables?

Solution:

Independent Variable: Amount of H2OH_2O. Dependent Variable: Height of the plant in cmcm. Control Variables: Type of seed, type of soil, and amount of sunlight.

Explanation:

To make it a fair test, Sarah only changed the amount of water. Everything else stayed the same so she knows the water is causing the growth difference.

Problem 2:

A student measures how long it takes for 5 g5\ g of salt to dissolve in water at different temperatures: 20∘C20 ^\circ C, 40∘C40 ^\circ C, and 60∘C60 ^\circ C. Identify the Independent Variable.

Solution:

The Independent Variable is the temperature of the water (TT).

Explanation:

The temperature is the factor the student is choosing to change to see how it affects the dissolving time.

Problem 3:

In a ramp experiment, a car travels 1.5 m1.5\ m in 3 s3\ s. Calculate the average speed.

Solution:

Speed=1.5 m3 s=0.5 m/s\text{Speed} = \frac{1.5\ m}{3\ s} = 0.5\ m/s

Explanation:

Using the formula for speed, we divide the distance by the time taken to find the rate of movement.