1bScientific Method and Measurement
Master the steps of the scientific method, design controlled experiments, and record measurements with proper SI units and significant figures.
Every experiment in physics — and every other science — relies on the scientific method and precise measurement. Without these tools, results cannot be trusted, compared, or built upon.
Lesson Overview
Science advances through a systematic process of observation, questioning, and testing. In this lesson you will learn the steps of the scientific method, how to design a controlled experiment, and how to record measurements using SI units and significant figures — the language of all quantitative science.
Key Concepts
Observation
Noticing a phenomenon using the senses or instruments
Hypothesis
A testable, falsifiable prediction about a phenomenon
Controlled Experiment
An experiment that changes one variable while holding all others constant
Independent Variable
The variable deliberately changed by the experimenter
Dependent Variable
The variable measured as a result of the experiment
SI Units
The International System of Units used worldwide in science
Significant Figures
Digits in a measurement that carry meaningful precision
Scientific Notation
A way to express very large or small numbers as a × 10ⁿ
A student notices that plants near a window grow taller than plants in a dark corner. She hypothesizes: 'Plants that receive more light will grow taller.' Identify the independent and dependent variables.
A physicist measures the length of a lab bench as 1.847 m. How many significant figures does this measurement contain?
Express the speed of light, 300,000,000 m/s, in scientific notation.
A student measures the mass of a sample five times and gets: 12.3 g, 12.4 g, 12.3 g, 12.4 g, 12.3 g. Are these results precise? Accurate? (True value = 15.0 g)
Round 0.004 506 to 3 significant figures.
List the steps of the scientific method in order.
Hint: Start with an observation and end with communicating results.
A student tests whether salt concentration affects the boiling point of water. Identify the independent variable, dependent variable, and two controlled variables.
Hint: What is being changed? What is being measured? What must stay the same?
How many significant figures are in the measurement 0.00720 kg?
Hint: Leading zeros are never significant; trailing zeros after a decimal point are.
Write 0.000 000 045 m in scientific notation.
Hint: Count how many places you move the decimal to get a number between 1 and 10.
Explain the difference between a hypothesis and a theory in science.
Hint: Think about the amount of evidence supporting each.
Key Vocabulary
Hypothesis
A testable, falsifiable prediction that explains an observation.
Example: 'Increasing temperature will increase the rate of a chemical reaction' is a hypothesis.
Controlled Variable
A factor kept constant throughout an experiment so it does not affect the results.
Example: Keeping the same amount of water for all plant groups is a controlled variable.
Significant Figures
The meaningful digits in a measured or calculated value, indicating precision.
Example: 12.30 cm has 4 significant figures; the trailing zero is significant.
SI Units
The International System of Units — the globally accepted standard for scientific measurement.
Example: The SI unit of length is the metre (m); of mass, the kilogram (kg).
Interactive Practice — 5 Questions
Which step of the scientific method comes immediately after forming a hypothesis?
How many significant figures are in 0.00340?
In an experiment testing how temperature affects reaction rate, what is the dependent variable?
Which of the following correctly expresses 56,200 in scientific notation with 3 significant figures?
A set of measurements is accurate but not precise. This means:
Independent Practice
Design a controlled experiment to test whether the height from which a ball is dropped affects the height of its bounce. Identify all variables.
A student records a mass as 0.005 060 kg. How many significant figures does this value have? Explain your reasoning.
Convert 9.81 × 10⁻² km to metres using SI prefixes. Show your work.
Explain the difference between accuracy and precision using a dartboard analogy.
★ A scientist repeats an experiment 30 times and gets consistent results, but another lab cannot reproduce them. What does this suggest about the original experiment? What should be done next?
ChallengeCommon Mistakes
Counting leading zeros as significant figures (e.g., saying 0.0045 has 4 sig figs).
Leading zeros only locate the decimal point — they are never significant. 0.0045 has 2 sig figs.
Confusing the independent variable with the dependent variable.
The independent variable is what you change; the dependent variable is what you measure as a result.
Writing scientific notation with a coefficient greater than 10 (e.g., 56 × 10³).
The coefficient must be between 1 and 10: 5.6 × 10⁴.
Math Tips
To count sig figs: ignore leading zeros; count all other digits including trailing zeros after a decimal point. For 0.004 50: sig figs are 4, 5, 0 → 3 sig figs.
For scientific notation, count how many places you move the decimal. Moving left → positive exponent; moving right → negative exponent.