How scientists ask questions — and actually answer them.
Watch first — this video shows how to think like a scientist when you spot something interesting.
SciShow Kids — "Think Like an Engineer: Let's Design a Solution!" (~5 min)
🔎 What do you notice?
Mia is making soup in Valencia, Spain. She drops some ingredients into the pot while the water heats up:
Ingredient
What happened?
Cork
Floated
Potato cube
Sank
Olive oil
Floated
A grape
Sank
Ice cube
Floated, then disappeared
A dried chickpea
Sank
Before reading further — what pattern do you see? Why do some things float and others sink? Write your idea in one sentence.
💡 Your Hypothesis
A hypothesis is an educated prediction — your best guess, with a reason. It follows the pattern:
"I think [thing] will happen because [reason]."
Write your own hypothesis for why things float or sink in water before continuing. (There's no wrong answer yet — you're doing science!)
📋 The Scientific Method — Six Steps
Observe — notice something interesting in the world
Question — turn the observation into a "Why?" or "What if?" question
Hypothesis — make a testable prediction with a reason
Experiment — design a fair test (only change one thing at a time)
Data & Results — record what actually happens
Conclusion — was your hypothesis supported? What did you learn?
Scientists repeat this cycle endlessly. A "wrong" hypothesis is still valuable — it rules something out and points toward the real answer.
⚖️ The Key Rule: Fair Tests
A good experiment changes only one variable at a time. Everything else stays the same. This is called a controlled experiment.
Example: to test whether the size of a grape affects sinking, you'd use grapes of different sizes — but the same water, same pot, same temperature.
🧪 Try It — The Orange Experiment
You need: one whole orange, a bowl of water, and nothing else.
Place the whole (unpeeled) orange in the water. What happens?
Take it out and peel it completely. Place the peeled orange in the water. What happens now?
Write down both results in a small table: Object | Floats? | Why I think so
Look at the peel. It's full of tiny pockets of air. What does this tell you about floating?
Conclusion hint: the peel adds air pockets, which reduce the orange's average density. You'll explore density properly in lesson s08.
Worked Examples
Example 1 — Spotting the Steps
Mia notices that her bread rises higher in Barcelona than in La Paz, Bolivia. She wants to know why.
Observation: Bread rises more at sea level than at high altitude.
Question: Does altitude (air pressure) affect how much bread rises?
Hypothesis: "I think bread rises more at sea level because air pressure is higher, which helps the yeast expand."
Experiment: Bake the same recipe at sea level (Barcelona) and at high altitude (La Paz), changing only the location.
Result: The sea-level loaf rose 8 cm; the high-altitude loaf rose 5 cm.
Conclusion: Altitude does affect bread rising. Hypothesis was supported.
Example 2 — Fixing a Bad Experiment
Mia's brother sets up this experiment: "I'll test whether sugar or salt dissolves faster. I'll put 1 spoon of sugar in hot water and 1 spoon of salt in cold water and stir the sugar more."
Problem 1: The water temperatures are different — that's two variables changing at once.
Problem 2: Stirring more also changes the result — another variable.
Fixed experiment: Use the same amount of each substance, in the same amount of water at the same temperature, with the same stirring.
Problems
Problem 1
Match each step of the scientific method to what Mia does:
What Mia does
Step (write the name)
She notices that ice floats in her glass.
___________
She asks: "Why does ice float but a metal spoon sinks?"
___________
She guesses: "Ice floats because it is less dense than liquid water."
___________
She tests 5 different objects in water and records what floats.
___________
She writes: "4 out of 5 floated. My prediction was partly right."
___________
— work on paper —
Problem 2
Write a hypothesis for each question. Use the format: "I think [prediction] because [reason]."
Does the colour of a flower affect how many bees visit it?
Does listening to music make you solve maths problems faster?
Do plants grow taller in sunlight or in shade?
— write your hypotheses —
Problem 3
Mia's friend tests: "Does the type of music affect how fast you run?" She has 10 runners listen to pop music and run 100 m, then has a different 10 runners listen to classical music and run 100 m. List two problems with this experiment design.
— work on paper —
Problem 4
Mia tests 20 seeds: she plants 10 in sandy soil and 10 in rich soil, waters them equally, and puts them all in the same sunny window. After 2 weeks, 7 sandy seeds sprouted and 9 rich-soil seeds sprouted. Calculate the sprouting rate (%) for each group. Which hypothesis does this support?
— work on paper —
Problem 5
Mia tests whether altitude affects how fast water boils. She records this data:
City
Altitude (m)
Boiling point (°C)
Valencia, Spain
15
100
Medellín, Colombia
1 495
95
Cusco, Peru
3 399
87
La Paz, Bolivia
3 640
86
Does boiling point increase or decrease with altitude?
Between Valencia and La Paz, what is the total change in boiling point?
Is the relationship between altitude and boiling point perfectly linear? How can you tell?
— work on paper —
Problem 6
Look at these hypotheses. For each one, say whether it is testable (you could design an experiment) or not testable (too vague or impossible). Explain briefly.
"Dogs are better than cats."
"Plants watered with sparkling water will grow taller than plants watered with still water."
"There are parallel universes."
"Cold water freezes faster than warm water when placed in the same freezer."
— work on paper —
Problem 7 Challenge
Mia predicts that bread rises faster at warmer temperatures. She bakes three identical loaves at 20 °C, 25 °C, and 30 °C and records rise time (in minutes): 90 min, 65 min, 45 min. Draw a rough sketch of a graph (time on y-axis, temperature on x-axis). Is this relationship linear? What would you predict the rise time at 35 °C to be? Justify your answer.
— sketch graph and answer —
Problem 8 Open
Design your own mini-experiment about something you can actually test at home or outside. Write: (1) your observation, (2) your question, (3) your hypothesis, (4) what you would change and what you would keep the same, (5) how you would record results.
— your experiment design —
Science check ✔ — The scientific method isn't a strict recipe. Real scientists jump between steps, revisit old hypotheses, and sometimes discover something completely different from what they were looking for. What matters is making sure your experiments are fair and your conclusions are honest — even when the result surprises you.
Show Answer Key
1.
Floats → Observation · "Why?" → Question · Guesses → Hypothesis · Tests 5 objects → Experiment · Writes "4/5 floated" → Conclusion (the Data/Results step is embedded in the experiment here)
2.
Answers vary — any reasonable hypothesis with a reason is correct. Example: "I think plants grow taller in sunlight because they need light energy to make food."
3.
Two problems: (1) Different people ran with each music type — individual fitness differences could explain the results. (2) The runners who listened second already ran once and might be tired (or warmed up). Fix: have the same people run twice, in random order, with a rest between.
4.
Sandy soil: 7/10 = 70%. Rich soil: 9/10 = 90%. The results support the hypothesis that rich soil leads to a higher germination rate.
5a.Boiling point decreases as altitude increases.5b.100 °C − 86 °C = 14 °C decrease from Valencia to La Paz.5c.Not perfectly linear — the altitude increases are not evenly spaced and neither are the boiling point drops. But there is a clear downward trend.6.
(1) Not testable — "better" is too vague and subjective.
(2) Testable — specific, measurable, controllable.
(3) Not testable — we have no way to observe or test parallel universes.
(4) Testable — this is the Mpemba effect; you could measure freezing time precisely.
7.The graph shows rise time decreasing as temperature increases. It is roughly linear in this range. At 35 °C, a linear estimate gives about 30 min (the gap is roughly −20 to −22 min per +5 °C). Exact answer may vary; any justified prediction near 25–35 min is good.
8.Open answer — there is no single correct response. Look for: a clear observation, a specific testable question, a hypothesis with a reason, exactly one variable changed, and a clear plan for recording results.
Next up → s02: Measurement & the Metric System
Scientists need to measure things accurately. You'll learn why the whole world (except one country…) uses the metric system, and how to convert between units without getting lost.