Scientific Variables and Laboratory Planning

Vocabulary flashcards covering the definitions of independent, dependent, and controlled variables, along with measurement principles, error types, and labeling conventions for Sec 1 and Sec 2 Science.

Independent variable ($IV$)

The one factor that is deliberately changed between trials to observe an effect; characterized by the question: "What am I changing?"

Dependent variable ($DV$)

The factor that is measured or recorded as a result of changing the $IV$; characterized by the question: "What am I recording?"

Controlled variables ($CVs$)

Every other factor that could affect the $DV$ but is held constant throughout all trials to ensure a fair test.

The Variable Naming Rule

Variables must be named as a measurable property of an object rather than just the object itself (e.g., "$\text{length of ruler overhanging the desk edge / cm}$ " instead of "ruler").

Independent Variable ($IV$) for a Simple Pendulum

$\text{length of string / cm}$ (measured from the pivot to the centre of the bob).

Dependent Variable ($DV$) for a Simple Pendulum

$\text{time for 10 complete oscillations / s}$ (or the vibration period).

Independent Variable ($IV$) for Osmosis Experiment

$\text{concentration of sucrose solution / mol\,dm}^{-3}$.

Dependent Variable ($DV$) for Osmosis Experiment

$\text{percentage change in mass of potato cylinder / \%}$.

Independent Variable ($IV$) for a Bouncing Ball

$\text{drop height / cm}$ (measured from the bottom of the ball to the floor).

Dependent Variable ($DV$) for a Bouncing Ball

$\text{bounce height / cm}$ (measured from the floor to the highest point of the ball after the first bounce).

Temperature Control Method

Conduct all trials at room temperature on the same day in the same room, or use a water bath set to the same temperature.

Volume Control Method

Measure with the same measuring cylinder and use the same volume (e.g., $200\,cm^{3}$) for every trial.

Mass Control Method

Weigh each specimen on the same electronic balance (e.g., to $0.01\,g$) and trim to the same dimensions before the trial.

"The effect of X on Y" Phrasing

A sentence structure where X represents the $IV$ and Y represents the $DV$.

"Repeat with…" Phrasing

A method description where the values listed (e.g., $10, 20, 30, 40\,cm$) identify the factor being varied as the $IV$.

Stirring Rate Control

Use a magnetic stirrer at the same setting, or stir manually with the same number of strokes per minute.

Controlled-variable Sentence Checkpoint

A complete answer that includes the name of the measurable $CV$, the exact value or method of fixing it, and a link to how changing it would affect the $DV$.

Random Error

An error that differs in magnitude and direction from one trial to the next, such as reaction time delay on a stopwatch, which can be reduced by repeating and averaging.

Systematic Error

An error that shifts all readings by the same amount in the same direction, such as parallax error when reading a ruler from the wrong eye level.

Parallax Error

A systematic error caused by the student's eye not being level with the measurement point on a scale, shifting the result away from the true value.

Fair Test Principle

The requirement to change only one variable ($IV$) while keeping all other potential factors ($CVs$) constant.

Confusing $DV$ with Method Of Measurement

A common mistake where the student names the instrument (e.g., "using a balance") rather than the actual measurable quantity (e.g., "$\text{percentage change in mass / \%}$ ").