The Scientific Endeavour is the overarching topic of Sec 2 IP Science. It treats science as a way of knowing: a disciplined process for building reliable knowledge about the natural world through observation, testable hypotheses, controlled experiments and conclusions based on evidence.
Every practical, data-response and planning question from now until the O-Level/IP examinations builds on these ideas. To be ready, you need to identify variables, design a fair test, work safely in the laboratory, choose and read the right measuring instrument, and judge whether the evidence supports a conclusion.
What these notes cover
- •The scientific method as a cycle
- •Models and theories are tentative
- •Variables and fair test design
- •Repeat readings and reliability
- •The seven scientific attitudes
- •Science, technology, society and the environment (STSE)
- •Hazard symbols and laboratory safety rules
- •The Bunsen burner: luminous vs non-luminous flame
- •SI units and choosing measuring instruments
- •Measuring volume, time and temperature
- •Parallax error, zero error, precision and accuracy
- •Common mistakes and exam technique
Key definitions
- Hypothesis
- A proposed explanation for an observation that can be tested by experiment. If no possible result could contradict the statement, it is not a scientific hypothesis.
- Fair test
- An experiment in which only the independent variable is changed and every other relevant variable is controlled.
- Parallax error
- An error in reading a scale that occurs when the eye is not placed perpendicular to the scale, directly in front of the marking being read.
- Zero error
- An error that occurs when an instrument does not read exactly zero when it should. One example is a micrometer screw gauge that does not show 0.00 mm when the anvil and spindle are closed.
- Precision and accuracy
- Precision is how close repeated readings are to one another. Accuracy is how close a reading is to the true value of the quantity being measured.
Key formulas
Micrometer screw gauge reading
reading = main scale reading + (thimble scale reading × 0.01 mm)
Read the main scale on the sleeve to the nearest 0.5 mm, checking for a visible half-millimetre mark. Then read the thimble division in line with the datum line. Quote the answer to two decimal places of a millimetre.
Period of a pendulum
T = t ÷ n
T is the period, the time for one complete oscillation (a full swing there and back). t is the total time measured and n is the number of complete oscillations timed, which should be 20 or more.
Correcting a zero error
corrected reading = observed reading − zero error
The zero error carries a sign. Subtract a positive zero error; subtracting a negative zero error means adding it back.
Volume of an irregular solid (displacement)
volume of solid = V₂ − V₁
V₁ is the initial volume of water in the measuring cylinder and V₂ is the volume once the solid is fully submerged.
Volume of a floating object (sinker method)
volume of object = V₃ − V₂
V₂ is the reading with water and the sinker fully submerged. V₃ is the reading with water, sinker and object all fully submerged. The water-alone reading is not needed.
Thickness of a beaker wall
thickness = (external diameter − internal diameter) ÷ 2
Measure the external diameter with the outside jaws and the internal diameter with the inside jaws of the vernier calipers.
Worked example
A cork floats on water, so a student ties it to a stone so that both are fully submerged in a measuring cylinder. Her readings are: water alone 30.0 cm³; water + stone 42.0 cm³; water + stone + cork 47.5 cm³. Find the volume of the cork.
- 1The rise in water level equals the volume of whatever is newly submerged, so volume of object = final reading − initial reading.
- 2Between the second and third readings, the only new object under the water is the cork.
- 3Volume of cork = 47.5 cm³ − 42.0 cm³ = 5.5 cm³.
- 4As a check, 47.5 cm³ − 30.0 cm³ = 17.5 cm³ is the combined volume of the stone and the cork, not the volume of the cork alone.
- 5Take each reading with the measuring cylinder on a flat bench, reading the bottom of the meniscus at eye level to avoid parallax error.
Watch out: Subtracting the first reading from the third gives 17.5 cm³, which is a very common wrong answer. Always ask between which two readings the cork alone entered the water.
Common mistakes
Mixing up the luminous and non-luminous flames
Wrong: Opening the air hole gives a luminous, orange-yellow flame.
Right: With the air hole open, combustion is complete and the flame is non-luminous: pale blue, hotter, no soot, and used for heating. With the air hole closed, combustion is incomplete and the flame is luminous: orange-yellow, cooler and sooty, and used when the burner is idle.
Believing that averaging removes zero error
Wrong: I took five readings and averaged them, so the zero error is eliminated.
Right: Averaging reduces random error only. A zero error is a systematic error that shifts every reading by the same amount. It must be subtracted from every reading, or added if the zero error is negative.
Saying the results prove the hypothesis
Wrong: This proves my hypothesis is correct.
Right: Write: "The results support the hypothesis." Theories and models are tentative and are revised or replaced when new evidence arrives.
Questions students ask
What is the difference between precision and accuracy in science?
Precision is how close repeated readings are to one another, and it is linked to the smallest division of the instrument. Accuracy is how close a reading is to the true value. A stopwatch that always reads 2 seconds fast gives readings that are precise but not accurate.
What are independent, dependent and controlled variables?
The independent variable is the one you deliberately change, and there should be only one. The dependent variable is the one you measure to see the effect. Controlled variables are all the other variables that could affect the result, and they are kept constant throughout so that the test is fair.
When do you use a luminous or non-luminous Bunsen flame?
Use the non-luminous flame for heating substances: the air hole is open, and the flame is blue, hotter and leaves no soot. Switch to the luminous flame when the burner is lit but not in use: the air hole is closed, and the orange-yellow flame is easy for everyone to see.
Why do you time 20 oscillations of a pendulum instead of one?
Human reaction time when starting and stopping a stopwatch causes an error at the start and at the end. Timing 20 or more oscillations and using T = t ÷ n spreads this error across all of them, so its effect on the period shrinks by a factor of 20.
In the full PDF
- •Labelled micrometer screw gauge scale diagrams, including how to check the zero reading
- •Further worked examples: identifying variables, writing a testable hypothesis, reading a micrometer, timing a pendulum, choosing hazard labels and responding to a laboratory fire
- •The full hazard-symbol table with example substances and precautions, plus first responses to common laboratory accidents
- •The seven scientific attitudes with examples, the parts of the Bunsen burner and common laboratory apparatus
- •The remaining three common mistakes and the full exam-technique phrasing guide
- •Section summaries and a final revision checklist