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Scientific Method Rain Experiment

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Scientific Method Rain Experiment

A class is testing how the depth of a shaving-foam “cloud” affects the number of coloured-water drops needed before the first drop reaches the water in a cup. Read the method and results, then use evidence to answer each question. This is a model of one part of the water cycle, not a real cloud. Do not handle shaving foam or coloured water unless an adult has approved the experiment.

Plan the investigation

Method: Put 200 mL of water in each of three identical clear cups. Prepare shaving-foam layers that are 2 cm, 3 cm and 4 cm deep, with one depth in each cup. Using a pipette, add coloured water to the centre of the foam, one drop at a time. For each trial, count the drops added before the first coloured drop reaches the water in the cup. Keep the cup size, starting water volume, coloured-water drop size and drop location the same. Repeat each foam-depth condition three times and calculate the mean.

Foam depth

Trial 1

Trial 2

Trial 3

Mean

2 cm

3 cm

28.3

4 cm

Think like a scientist

Answer using the method and results shown above. Include evidence from the table when asked.

1.Write a testable question for this investigation. It should name what is changed and what is measured.

2.Predict what will happen to the number of drops needed as the foam layer gets deeper. Give a reason for your prediction.

3.Identify the independent variable, the dependent variable and one control variable in this experiment.

4.Why should the class use the same cup size, starting water volume and drop location for every trial?

To keep other factors from affecting the results
To make the coloured water change colour
To make the foam depth impossible to measure
To ensure every trial has a different result

5.Calculate the mean number of drops for the 3 cm foam layer. Show or describe your calculation.

6.Compare the mean for the 2 cm layer with the mean for the 4 cm layer. What pattern do the results show?

7.Which foam depth had the greatest spread between its highest and lowest trial results? State the spread.

8.True or false: The results prove that real rain clouds release rain in exactly the same way as shaving foam.

TrueFalse

9.The 3 cm trials were 27, 30 and 28 drops. Explain why repeating a trial is useful, and suggest one reason the results might differ slightly.

10.Use the results to state whether the prediction in Question 2 is supported. Include at least two pieces of numerical evidence and one limitation of the model.

11.Suggest one improvement that would make the investigation fairer or the measurements more reliable. Explain how it would help.