Steps of an investigation
A scientific investigation follows a clear sequence: identify the problem, make a hypothesis, plan the experiment, collect data, analyse results and draw a conclusion. Good planning controls the variables so the result is fair and reliable.
Variables
There are three types of variable:
- Manipulated variable — the one you deliberately change.
- Responding variable — the one you measure as a result.
- Constant (controlled) variable — kept the same to keep the test fair.
A hypothesis is a testable statement linking the manipulated and responding variables, for example: "The greater the force, the greater the acceleration."
Key idea
A graph line of best fit shows the relationship. Gradient = (change in y) ÷ (change in x), and a straight line through the origin means the two quantities are directly proportional.
Accuracy, precision and sensitivity
Accuracy is how close a reading is to the true value. Precision is how close repeated readings are to each other. Sensitivity is the ability of an instrument to detect a small change. Repeating readings and taking an average reduces random error.
Worked example
A student measures the period of a pendulum 5 times: 2.0, 2.1, 1.9, 2.0 and 2.0 s. The average period is (2.0 + 2.1 + 1.9 + 2.0 + 2.0) ÷ 5 = 10.0 ÷ 5 = 2.0 s. Averaging reduces random error and improves accuracy.
Remember
- Only ONE manipulated variable at a time keeps a test fair.
- Accuracy ≠ precision: a precise set can still be inaccurate.
- Repeat readings and average to reduce random error.