Australian Curriculum v9 / ACiQ Year 8 Science - Unit 4 - Investigable questions, predictions and hypotheses

Investigable questions, predictions and hypotheses

Develop testable questions, justified predictions and hypotheses that identify measurable variables and a scientific rationale.

Updated 2026-07-26 - 12 min read

Investigable questions, predictions and hypotheses is taught here as a connected set of decisions, not a list of facts. Work through the prerequisite recall, explicit models, carefully faded examples, misconception repairs and transfer task before using the target in Check, Practice, Review or Rapid Revision.

This note is designed to work with the guided lessons, curated practice, flashcards, Tutor context, Review and Rapid Revision for the same canonical target. The same three evidence checks are used throughout, so feedback can route a learner back to the precise idea that needs repair.

Form an investigable question

An investigable question identifies a variable to change or compare, a measurable outcome and a feasible system or population. This relationship must be selected from the quantities and conditions in the problem, then checked against the context.

A dependable reasoning routine

  1. Define the system or phenomenon and identify the change being explained.
  2. Trace the mechanism for form an investigable question in causal order rather than listing disconnected terms.
  3. Link each claim to an observation, measurement, model or accepted scientific relationship.
  4. State the boundary of the conclusion: what was tested, what remains uncertain and what evidence would strengthen it.

Repair: Scope the question to observable variables, available methods, time and ethical limits.

The repair matters because the shortcut may appear to work in one familiar example while failing when the system boundary, causal mechanism, variable or evidence limit changes. Use the routine above to make the reasoning visible enough for another learner to verify.

Example 1.1

Which is most investigable in a classroom?

Step 1 - identify the governing idea: An investigable question identifies a variable to change or compare, a measurable outcome and a feasible system or population.

Step 2 - apply it to this evidence: Both variables are measurable and feasible.

Result: How does water temperature affect the time for a sugar cube to dissolve?

The evidence-to-mechanism link is: Both variables are measurable and feasible. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • Why is water important? — It conflicts with the stated mechanism or evidence: Both variables are measurable and feasible.
  • What is the best drink? — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • How does the universe work? — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Example 1.2

Improve 'Do plants like light?'

Step 1 - identify the governing idea: An investigable question identifies a variable to change or compare, a measurable outcome and a feasible system or population.

Step 2 - apply it to this evidence: The revision operationalises exposure, outcome and time.

Result: How does daily light duration affect mean seedling height over 14 days?

The evidence-to-mechanism link is: The revision operationalises exposure, outcome and time. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • Are plants good? — It conflicts with the stated mechanism or evidence: The revision operationalises exposure, outcome and time.
  • Does light exist? — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • Why are leaves green forever? — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Example 1.3

Why is 'Does music make everyone smarter?' poorly scoped?

Step 1 - identify the governing idea: An investigable question identifies a variable to change or compare, a measurable outcome and a feasible system or population.

Step 2 - apply it to this evidence: Key variables and feasible boundaries are missing.

Result: The population, exposure and measurable meaning of smarter are undefined

The evidence-to-mechanism link is: Key variables and feasible boundaries are missing. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • It contains a question mark — It conflicts with the stated mechanism or evidence: Key variables and feasible boundaries are missing.
  • Music cannot be studied — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • All people are identical — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Write a reasoned hypothesis

A hypothesis predicts the direction of a relationship and explains why using relevant scientific knowledge. This relationship must be selected from the quantities and conditions in the problem, then checked against the context.

A dependable reasoning routine

  1. Define the system or phenomenon and identify the change being explained.
  2. Trace the mechanism for write a reasoned hypothesis in causal order rather than listing disconnected terms.
  3. Link each claim to an observation, measurement, model or accepted scientific relationship.
  4. State the boundary of the conclusion: what was tested, what remains uncertain and what evidence would strengthen it.

Repair: Use if/when, then and because to connect variables with a testable mechanism.

The repair matters because the shortcut may appear to work in one familiar example while failing when the system boundary, causal mechanism, variable or evidence limit changes. Use the routine above to make the reasoning visible enough for another learner to verify.

Example 2.1

Best hypothesis for dissolving and temperature?

Step 1 - identify the governing idea: A hypothesis predicts the direction of a relationship and explains why using relevant scientific knowledge.

Step 2 - apply it to this evidence: It gives direction and mechanism.

Result: If water temperature increases, dissolving time will decrease because faster particle motion increases collisions

The evidence-to-mechanism link is: It gives direction and mechanism. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • Hot water is better — It conflicts with the stated mechanism or evidence: It gives direction and mechanism.
  • Sugar will dissolve — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • Temperature changes things — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Example 2.2

A student predicts more ramp height gives more toy-car speed. What completes the rationale?

Step 1 - identify the governing idea: A hypothesis predicts the direction of a relationship and explains why using relevant scientific knowledge.

Step 2 - apply it to this evidence: The energy model explains the predicted direction.

Result: More gravitational potential energy can transform to kinetic energy

The evidence-to-mechanism link is: The energy model explains the predicted direction. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • Tall ramps look faster — It conflicts with the stated mechanism or evidence: The energy model explains the predicted direction.
  • Cars always speed up forever — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • Height creates mass — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Example 2.3

Can a hypothesis be unsupported by results?

Step 1 - identify the governing idea: A hypothesis predicts the direction of a relationship and explains why using relevant scientific knowledge.

Step 2 - apply it to this evidence: A hypothesis is testable, not guaranteed.

Result: Yes; evidence may not support it, and the explanation should then be evaluated

The evidence-to-mechanism link is: A hypothesis is testable, not guaranteed. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • No; it becomes true when written — It conflicts with the stated mechanism or evidence: A hypothesis is testable, not guaranteed.
  • No; results must be changed — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • Yes; therefore evidence is useless — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Operationalise variables

Variables must be defined by exactly how they will be changed, measured or held constant. This relationship must be selected from the quantities and conditions in the problem, then checked against the context.

A dependable reasoning routine

  1. Define the system or phenomenon and identify the change being explained.
  2. Trace the mechanism for operationalise variables in causal order rather than listing disconnected terms.
  3. Link each claim to an observation, measurement, model or accepted scientific relationship.
  4. State the boundary of the conclusion: what was tested, what remains uncertain and what evidence would strengthen it.

Repair: Specify an observable measure, unit, timing and consistent method.

The repair matters because the shortcut may appear to work in one familiar example while failing when the system boundary, causal mechanism, variable or evidence limit changes. Use the routine above to make the reasoning visible enough for another learner to verify.

Example 3.1

Best operational definition of plant growth?

Step 1 - identify the governing idea: Variables must be defined by exactly how they will be changed, measured or held constant.

Step 2 - apply it to this evidence: The definition is observable, quantified and repeatable.

Result: Change in stem height in millimetres measured every two days

The evidence-to-mechanism link is: The definition is observable, quantified and repeatable. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • How healthy it looks — It conflicts with the stated mechanism or evidence: The definition is observable, quantified and repeatable.
  • Whether it is nice — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • Its final colour only — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Example 3.2

In a ramp test, why specify release without pushing?

Step 1 - identify the governing idea: Variables must be defined by exactly how they will be changed, measured or held constant.

Step 2 - apply it to this evidence: A consistent release isolates ramp height more effectively.

Result: It controls variation in initial force and speed

The evidence-to-mechanism link is: A consistent release isolates ramp height more effectively. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • It changes the dependent variable name — It conflicts with the stated mechanism or evidence: A consistent release isolates ramp height more effectively.
  • It makes repeats unethical — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • It measures mass — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Example 3.3

How could 'light intensity' be operationalised?

Step 1 - identify the governing idea: Variables must be defined by exactly how they will be changed, measured or held constant.

Step 2 - apply it to this evidence: The procedure defines the quantity and measurement conditions.

Result: Lux measured at leaf height with the same light meter position

The evidence-to-mechanism link is: The procedure defines the quantity and measurement conditions. Notice that the conclusion does not extend beyond the stated system or evidence. A scientific explanation must trace cause and effect, not only name the relevant vocabulary.

Why the alternatives fail:

  • Bright or dark by opinion — It conflicts with the stated mechanism or evidence: The procedure defines the quantity and measurement conditions.
  • Lamp colour only — It changes the system boundary or claims a cause that the supplied observations do not establish.
  • Time of lunch — It extends the conclusion beyond the evidence. A valid answer must preserve the variables, sequence and uncertainty in the prompt.

Retrieval check

Try these without looking back at the examples.

  1. Improve 'Do plants like light?'
  2. A student predicts more ramp height gives more toy-car speed. What completes the rationale?
  3. In a ramp test, why specify release without pushing?

Answers

  1. How does daily light duration affect mean seedling height over 14 days? — The revision operationalises exposure, outcome and time.
  2. More gravitational potential energy can transform to kinetic energy — The energy model explains the predicted direction.
  3. It controls variation in initial force and speed — A consistent release isolates ramp height more effectively.

Transfer task

Find an unfamiliar example from school, daily life, a credible news source or another subject. Explain which of the three evidence checks applies. Complete the task, then audit your own response: identify the evidence used, the relationship applied, one plausible misconception and the final reasonableness check. If a peer could not reproduce your reasoning, add the missing step.

Sources