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Scientific Enquiry - Planning fair tests and identifying variables

Grade 5IGCSE

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 at a time, while all other conditions are kept the same to ensure the results are valid.

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The Independent Variable is the factor that you purposely change in an experiment. For example, changing the temperature of water from 20∘C20^\circ C to 40∘C40^\circ C.

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The Dependent Variable is the factor that you measure or observe to see how it responds to the change. For example, measuring the time in seconds (ss) it takes for sugar to dissolve.

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Control Variables are the factors that are kept constant throughout the experiment. If you are testing how much light a plant needs, you must keep the amount of water (e.g., 50 ml50\ ml) and the type of soil the same.

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To improve Reliability, an experiment should be repeated at least 33 times. Scientists then calculate the average (mean) of their results.

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Measurements must include correct units, such as centimeters (cmcm) for length, grams (gg) for mass, and milliliters (mlml) for volume.

📐Formulae

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

ΔT=Tfinal−Tinitial\Delta T = T_{final} - T_{initial}

Volume of a liquid=V ml\text{Volume of a liquid} = V\ ml

💡Examples

Problem 1:

Anish wants to find out if the temperature of water affects how quickly 5 g5\ g of salt dissolves. Identify the Independent, Dependent, and two Control variables.

Solution:

Independent Variable: Temperature of the water (∘C^\circ C); Dependent Variable: Time taken to dissolve (ss); Control Variables: Volume of water (mlml) and the mass of salt (5 g5\ g).

Explanation:

To make it a fair test, Anish only changes the temperature. He measures the time it takes for the salt to disappear (dependent). He must keep the amount of water and salt the same (controls) so they don't interfere with the results.

Problem 2:

A student measures the distance a toy car travels in three trials: 120 cm120\ cm, 125 cm125\ cm, and 115 cm115\ cm. Calculate the average distance.

Solution:

Average=120+125+1153=120 cm\text{Average} = \frac{120 + 125 + 115}{3} = 120\ cm

Explanation:

To find the average, you add the results of all trials together and divide by the total number of trials (33).

Problem 3:

If a scientist is testing how the height of a ramp affects the speed of a marble, why must they use the same marble for every test?

Solution:

The mass and size of the marble are Control Variables.

Explanation:

If the scientist changed the marble to a heavier one, they wouldn't know if the speed changed because of the ramp height or because of the different marble weight. This would make the test 'unfair'.