DoAssignment.ca

A1.5 · Conduct inquiries safely while controlling relevant variables

Learn to conduct inquiries safely while controlling relevant variables through clear examples and targeted practice.

Ontario Grade 12 Physics

Scientific Investigation Skills and Career Exploration

Planning fair investigations and judging the evidence

A physics inquiry uses observations or measurements to answer a question. A useful inquiry must be safe, and its procedure must make clear what is being changed and what is being measured. It must also control relevant variables: factors that could affect the result but are not the focus of the question. This lesson focuses on planning and carrying out inquiries with those priorities. It does not treat a suggested procedure or a predicted outcome as if it were a completed experiment.

What you will learn

1. Set up the question and physical description

Begin with the SPH3U habit of describing motion or an interaction in a clear way. Define the physical system: the object or group of objects being studied. For example, in an inquiry about a cart rolling down a ramp, the cart is the system. State the reference frame, which is the viewpoint used to describe position and motion. A suitable choice is the laboratory floor. Choose a positive direction as well. For the ramp example, positive could point down the ramp. These choices make descriptions of direction consistent.
A scalar has magnitude only, such as time or mass. A vector has magnitude and direction, such as displacement or force. When an inquiry involves a vector, record enough information to preserve its direction. Do not treat a direction-sensitive result as though it were only a number.
Write a focused question before choosing equipment. It should name the factor you plan to change and the result you plan to measure. For instance, a proposed inquiry might ask how ramp angle affects the time for a cart to travel a fixed distance. This is a plan, not evidence that the cart has been tested.

2. Identify and control variables

A variable is a quantity or condition that can take different values. The independent variable is the factor deliberately changed. The dependent variable is the result measured or observed. A controlled variable is a relevant factor kept the same so that the comparison is meaningful. These labels describe the role of a variable in a particular inquiry; the same quantity can play different roles in a different question.
In the ramp question, ramp angle would be the independent variable, and travel time over a fixed distance would be the dependent variable. Distance, the cart, the release method, and the timing method could be relevant controlled variables. If distance changed along with angle, a change in travel time could not be linked clearly to angle alone. Controlling a variable means planning how to keep it consistent and checking that the procedure does so.
Not every possible factor needs to be controlled. Focus on factors that could affect the measured result. State how each important one will be held steady. Use the same equipment when practical, mark the same start and finish positions, and use a consistent release method. If a factor cannot be kept constant, record it and explain how it may affect the comparison. Do not claim perfect control when the procedure cannot support that claim.
A fair comparison changes the intended independent variable while keeping relevant conditions consistent. Repeat observations can help reveal whether results are consistent, but repetition does not fix an unsafe procedure or an uncontrolled change. Record the method and conditions clearly enough that another person can understand what was done.

3. Make safety part of the procedure

A hazard is something that could cause harm. Risk is the chance that harm could occur under the planned conditions. Before starting, inspect the equipment and workspace, identify likely hazards, and decide how to reduce risk. Follow the teacher's instructions and any required safety rules. Do not begin until the procedure and equipment have been approved when approval is required.
Safety steps depend on the inquiry. A moving cart needs a clear path and a way to prevent it from reaching an edge. A circuit inquiry requires checking the intended circuit and power source before connecting it. An inquiry involving a magnet needs care with objects that can be affected by the magnet. These are planning examples, not reports of completed tests. Use only equipment and procedures suitable for the classroom and the specific task.
Keep the workspace orderly. Use equipment as directed, keep attention on the task, and avoid actions that could expose you or others to a hazard. If equipment is damaged, a condition becomes unsafe, or the procedure differs from the approved plan, stop and tell the teacher. Do not improvise a new method to keep an inquiry going.
Safety and variable control support each other. A consistent procedure is easier to check for hazards, and a safer setup can make observations more repeatable. Still, a result is not trustworthy merely because the procedure was safe. The variables and measurements must also suit the question.

4. Record evidence and judge the inquiry

Evidence is information gathered to answer the question. Measured evidence comes from observations or measurements actually collected while carrying out an inquiry. A prediction is an expected result. A proposed procedure describes what someone plans to do. A simulation is a model run using chosen inputs. Keep these categories distinct: a predicted, proposed, or simulated result is not a physical measurement from a classroom investigation.
Before collecting evidence, decide what will be recorded and in what units. Use suitable measuring tools and a consistent method. Record observations honestly, including results that do not match a prediction. Do not invent values or change a record to make a pattern look clearer. If a measurement is difficult or a condition changes, note that limitation.
Afterward, compare the recorded evidence with the question. Ask whether the independent variable changed as planned, whether the dependent variable was measured consistently, and whether relevant controlled variables stayed consistent. Consider whether a safety issue or procedural change affected the observations. A conclusion should be limited to what the evidence supports.
For a proposed or simulated procedure, use future or conditional language. For example, say what would be measured or what a model predicts. Reserve statements about what was measured for an inquiry that was actually carried out. This distinction makes the status of the evidence clear.

Worked example

Planning a ramp inquiry

A student proposes asking whether ramp angle affects the time a cart takes to travel a marked distance. Identify the system and frame, the variables, and two controls. State one safety step. No measurements have been collected.
  1. Describe the system
    The cart is the physical system. Use the laboratory floor as the reference frame. Choose down the ramp as the positive direction for describing the cart's motion.
  2. Sort the variables
    The ramp angle is the factor to change, so it is independent. The travel time is the result to measure, so it is dependent. Keep the marked travel distance and the cart the same for each planned comparison.
  3. Plan the safety step
    Keep the cart's path clear and arrange the setup so the cart cannot roll off an edge. This is a proposed procedure, not a report of a test already performed.
Answer: System: cart. Frame: laboratory floor. Positive direction: down the ramp. Independent variable: ramp angle. Dependent variable: travel time. Two controls: distance and cart. Safety step: provide a clear path and prevent the cart from reaching an edge.
Check: No travel-time evidence exists until the procedure is actually carried out and observations are recorded.

Worked example

Finding a control problem

A proposed inquiry changes the ramp angle and also changes the cart's start-to-finish distance. The measured result is travel time. Explain why this design cannot isolate the effect of angle and suggest a correction.
  1. Identify the intended comparison
    The question is about the effect of angle, so angle is the independent variable and should be the factor deliberately changed.
  2. Identify the confounding change
    Distance can also affect travel time. Because both distance and angle change, a difference in time cannot be attributed clearly to angle alone.
  3. Revise the plan
    Mark one fixed start-to-finish distance and use it for every angle. Keep other relevant conditions, such as the cart and release method, consistent as well.
Answer: Keep the travel distance fixed while changing angle. Then measure travel time using the same method.
Check: The correction changes the intended factor while controlling a relevant alternative influence.

Worked example

Reporting the status of evidence

A group writes, “The cart took a shorter time at the steeper angle.” The group has only written a plan and has not used a cart. Rewrite the statement accurately and name evidence that would be needed to support the original claim.
  1. Distinguish plan from result
    The group has no measured evidence. It should not report a travel time or describe an observed comparison.
  2. Use proposal language
    State what the group plans to investigate and what it would measure. This makes clear that the procedure has not yet been carried out.
  3. Name needed evidence
    To support the original claim, the group would need recorded travel times at the compared angles, collected with the same distance and a consistent method.
Answer: Accurate wording: “We propose to investigate whether travel time changes with ramp angle by measuring the time over a fixed distance.” The original claim would require actual recorded times from the inquiry.
Check: The revised statement reports a plan, not an invented observation.

Common mistakes and how to avoid them

Calling every quantity that is not measured a controlled variable.
Correction: A controlled variable is a relevant factor that could affect the result and is deliberately kept consistent.
Changing more than one important factor and attributing the result to only one.
Correction: Change the intended independent variable and control other relevant factors where possible.
Writing a predicted or simulated result as if it were measured in a physical inquiry.
Correction: Label predictions, proposals, simulations, and collected measurements accurately.
Continuing when the setup is unsafe or differs from the approved procedure.
Correction: Stop, make the area safe if possible without added risk, and inform the teacher.

Lesson summary

Check your understanding

Question 1

In a proposed inquiry that changes wire length and measures current, which quantity is the dependent variable?
  1. Wire length
  2. Current
  3. The reference frame
  4. The safety procedure
Show answer and explanation
Current
Current is the dependent variable because it is the result being measured. Wire length is the factor deliberately changed.

Question 2

A group predicts that a cart will move faster on a steeper ramp but has not tested the setup. What may it report?
  1. That it measured a higher speed
  2. That the prediction is a measured result
  3. That it predicts a change and proposes a way to test it
  4. That the inquiry proves the prediction
Show answer and explanation
That it predicts a change and proposes a way to test it
A prediction can be reported as a prediction. It is not measured evidence unless the inquiry is carried out and observations are recorded.

Question 3

During an inquiry, a support becomes loose. What is the best response?
  1. Continue but omit the affected observations
  2. Hold the support while another person continues
  3. Stop and inform the teacher
  4. Change the procedure without telling anyone
Show answer and explanation
Stop and inform the teacher
A loose support may create a hazard and means the setup no longer matches the plan. Stop and tell the teacher rather than improvising.

Key terms

Physical system
The object or group of objects being studied.
Reference frame
The viewpoint used to describe position and motion.
Scalar
A quantity with magnitude only.
Vector
A quantity with magnitude and direction.
Independent variable
The factor deliberately changed in an inquiry.
Dependent variable
The result measured or observed in an inquiry.
Controlled variable
A relevant factor kept consistent during a comparison.
Hazard
Something that could cause harm.

Continue through SPH4U

View the complete SPH4U Ontario Grade 12 Physics curriculum and lessons

About this lesson and its review

Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 12 Physics (SPH4U), expectation A1.5. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

Official curriculum reference

Report a correction or ask a question