Scientific investigation: observation, hypothesis and fair tests

The steps of the scientific method are out of order: experimentation, observation, conclusions and hypothesis. Write them in the correct order and explain in one sentence what is done in each step.

Match each stage of the scientific method with what is done in it:

1. a) Observation
2. b) Hypothesis
3. c) Experimentation
4. d) Conclusions

1) A possible explanation for what happens is proposed.

2) An event is carefully observed and recorded.

3) The results are compared with the initial idea.

4) A test is designed and carried out to check the idea.

State whether each sentence is an observation or a hypothesis:

1. a) "This morning the playground was wet."
2. b) "I think it rained overnight."
3. c) "The swimming pool water is at $24\ ^\circ\text{C}$."
4. d) "If I leave my bike outside when it rains, it will rust faster."

Vera has two geraniums on her balcony: the one in the sun is taller than the one in the shade.

1. a) Write down the observation Vera has made.
2. b) Formulate a hypothesis to explain what she sees.

During a meal in the garden, Nil notices that the ice cubes in his glass melt much faster than they did on the day he used them in winter.

1. a) Is what Nil did an observation or a hypothesis?
2. b) Write a scientific question about this fact.

The TV remote control at Aitana's house stops working, and her father says: "I'm sure the batteries are flat".

1. a) Which stage of the scientific method does this sentence represent?
2. b) What would you do to check whether it is true?

Classify these statements into "scientific hypotheses" (can be tested with an experiment) or "non-scientific", and justify one from each group:

1. a) "On Fridays I have bad luck in exams."
2. b) "A new ball bounces more than an old ball."
3. c) "Salt water boils at a higher temperature than plain water."
4. d) "Black cats bring bad luck."

In an experiment, the slope of a ramp is changed to see how a toy car rolls. The setup is shown in the figure:

1. a) Explain in your own words what a variable is in an experiment.
2. b) Which variable is changed in this case?

Hugo wants his toast done just right and tries three times: $1$ minute, $2$ minutes and $3$ minutes, and writes down how each one turns out. Which stage of the scientific method is Hugo using? Justify your answer.

Aoife's soup cools down faster in a shallow plate than in a deep bowl.

1. a) Formulate a hypothesis that explains this.
2. b) Describe a simple experiment to test it and state what you would measure.

Bread in the kitchen drawer goes mouldy faster than bread kept in the fridge.

1. a) Formulate a hypothesis that explains this.
2. b) Design a simple test: what you would change, what you would observe, and what important factor must stay the same (control variable).

You want to find out whether an egg floats more easily in very salty water than in salt-free water. Observe the setup in the figure:

Write down:

1. a) Your hypothesis.
2. b) The variable you change.
3. c) The variable you observe or measure.
4. d) Two things that must be kept the same in both glasses.

Cian sets lentils to germinate in two glasses with damp cotton wool: one on the window sill and the other inside a dark cupboard.

1. a) Which variable is he changing?
2. b) Which variable will he measure to make a comparison?
3. c) Name two variables he must keep the same to ensure a fair test.

To find out whether light affects plant growth, Chloe places a pot with new soil on the window sill and another with old soil in a cupboard.

1. a) Will she be able to tell if light has an effect?
2. b) Explain the mistake she made.
3. c) How would you correct it?

You leave two identical glasses containing $100\ \text{mL}$ of water on the window sill, one covered with cling film and the other uncovered. The figure shows the setup at the start of the experiment:

1. a) Predict what will happen to the water level in each glass after one week.
2. b) Explain the role of the covered glass in the experiment.
3. c) State what you would measure and when, in order to test your prediction.

You want to test whether water temperature affects the rate at which sugar dissolves. Design a complete experiment indicating:

1. a) The hypothesis.
2. b) The variable you will change (independent) and the one you will measure (dependent).
3. c) Two variables you will keep the same (control variables).
4. d) The steps you would follow and the expected result if your hypothesis is correct.

Leo wants to know whether a drink cools down faster in the fridge or in the freezer. He puts a large bottle of soft drink in the fridge and a small can in the freezer, and measures the time each takes to reach $8\ ^\circ\text{C}$.

1. a) Point out the flaws in the design.
2. b) Redesign the experiment so that it is a fair test.
3. c) Explain why only one factor at a time should be changed in an experiment.

Izan repeats the same experiment three times and measures the time it takes for an ice cube to melt: $8$ minutes, $8.5$ minutes and $20$ minutes.

1. a) Which value seems suspicious? Why?
2. b) What should Izan do with that data point before drawing conclusions?
3. c) Explain why experiments are repeated multiple times in science.

Your friend Enzo claims: "I run faster with my new trainers".

1. a) Turn his claim into a testable hypothesis.
2. b) Propose a simple experiment indicating what you would measure and what should be kept the same.

Nadia notices ants on the pavement marching in a line towards a piece of biscuit. For this event, write down:

1. a) An observation and a scientific question.
2. b) A hypothesis and a sentence describing the first test you would carry out to check it.

Aoife is certain that, if dropped at the same time from the same height, a heavy ball always hits the ground before a light one. However, when she drops a basketball and a tennis ball, they both land at almost the same time.

1. a) Explain what a scientist should do when the results do not support their hypothesis.
2. b) Write a new hypothesis that Aoife could test now.

"If I wear my lucky shirt, my team wins."

1. a) Explain why this statement, as it is worded, is not a good scientific hypothesis.
2. b) Rewrite a similar statement that can be tested with an experiment.
3. c) Briefly describe how you would test it.

Cian's drone will not turn on.

1. a) Propose three different hypotheses to explain this and rank them from most to least likely in your opinion.
2. b) Describe a simple test to rule out each one, starting with the easiest to check.

An advertisement claims: "CrecePlus fertiliser makes plants grow twice as fast".

1. a) What experiment would you want to see to believe the advertisement? Describe the control group, what would be measured, and for how long.
2. b) Explain why a photo of a giant plant is not sufficient.