What is the scientific method?
Science is a way of finding out things that we can check with evidence. Evidence means facts from careful observation and measurement.
The scientific method is not a strict recipe. It is a loop of steps:
- Observe: notice something using your senses or instruments.
- Question: ask a question that a test can answer.
- Hypothesis: a clear, testable explanation or prediction, often written "If …, then …".
- Experiment: a fair test to check the hypothesis.
- Analyse: organise data in tables and graphs, look for patterns.
- Conclude and share: say whether the data support the hypothesis, and report it.
If the data do not support the hypothesis, that is still progress. You change the hypothesis and test again.
Questions and hypotheses
A good scientific question can be tested and measured. "Do plants grow taller with more light?" is testable. "Are roses the most beautiful flower?" is not, because beauty cannot be measured the same way by everyone.
A hypothesis is a possible answer based on what you already know. It must be falsifiable: a test could show it is wrong. Example: "If a plant gets more hours of light, then it will grow taller in two weeks."
A prediction says what you expect to measure if the hypothesis is true.
Variables and a fair test
- Independent variable: the ONE thing you change on purpose (hours of light).
- Dependent variable: the thing you measure, which may depend on it (plant height in cm).
- Controlled variables: everything you keep the same (water, soil, pot size, seed type, temperature).
A fair test changes only the independent variable. Then any difference must be caused by it.
The control group gets no treatment (0 hours of extra light, or a dummy pill) so you have something to compare with. The experimental group gets the treatment.
Safety and ethics: plan risks (heat, glass, chemicals), treat living things and people with care, get consent for surveys, and never change or invent data.
Data: measure, repeat, analyse
Record data in a table with SI units (m, kg, s, °C). Use the right instrument and read it carefully.
- Repeat each test (at least 3 times) and find the mean = sum ÷ number of readings. This reduces the effect of random errors.
- Accuracy = how close to the true value. Precision = how close repeated readings are to each other.
- Random error scatters readings (e.g. reaction time). Systematic error shifts every reading the same way (e.g. a scale that reads 2 g too high).
- An anomaly (outlier) is a reading far from the others; check it and repeat.
Plot a graph: independent variable on the x-axis, dependent on the y-axis. Look for a trend. Remember: two things rising together (correlation) does not always mean one causes the other.
Conclusions, theories and how science grows
A conclusion answers the question using the data: "More light gave taller plants up to about 12 hours." Say that the data support the hypothesis; one experiment never proves it forever.
Inductive reasoning: from many observations to a general rule (every metal I heated expanded, so metals expand when heated). Deductive reasoning: from a general rule to a specific prediction (metals expand when heated; this rail is metal; so it will expand in summer). The hypothetico-deductive method joins them: make a hypothesis, deduce a prediction, test it.
A scientific model is a simplified picture (a globe, a formula, a computer simulation). A law describes what happens; a theory is a well-tested explanation of why. Scientists share work through reports and peer review so others can repeat it. Example: Ibn al-Haytham (about 1020) tested ideas about light with careful experiments; Galileo timed rolling balls instead of trusting old books.
Key formulas and definitions
- Mean = sum of readings ÷ number of readings
- Range = highest − lowest reading
- Independent variable → x-axis; dependent variable → y-axis
- Fair test: change 1, measure 1, keep the rest the same
- Hypothesis form: If [change], then [effect]
Worked examples
1. Does salt make water boil at a higher temperature? Name the variables.
Independent: amount of salt. Dependent: boiling temperature (°C). Controlled: volume of water, same pan, same flame.
2. Three readings of time for a ball to fall: 0.52 s, 0.49 s, 0.55 s. Find the mean and range.
Mean = 1.56 ÷ 3 = 0.52 s. Range = 0.55 − 0.49 = 0.06 s.
3. Write a testable hypothesis about sugar dissolving.
If the water is hotter, then the sugar will dissolve in less time.
4. Readings 20.1, 20.3, 26.0, 20.2 cm. What should you do?
26.0 is an anomaly. Check for a mistake, repeat that trial, and find the mean of the reliable readings (20.2 cm).
Common mistakes
- Changing two things at once, so you cannot tell which one caused the result.
- Doing a test only once and trusting that single result.
- Saying the experiment "proved" the hypothesis. Data support or do not support it.
- Mixing up the independent variable (you change it) and the dependent variable (you measure it).