Review for Science Test: Variables and Observations

Experimental Variables in Scientific Investigation

  • Fundamental Principle of a Fair Test:

    • In a scientific investigation, only one factor is changed at a time.
    • Changing only a single condition ensures that any observed effects or outcomes are directly caused by the manipulated factor and not by extraneous variables.

  • Independent Variable:

    • Definition: What is changed in an experiment by the investigator.
    • Easy Way to Remember: "Independent = I change it" (associating the letter "I" with the person actively altering the variable).

  • Dependent Variable:

    • Definition: What is measured in an experiment to assess the outcome.
    • Easy Way to Remember: "Dependent = measure it" (focusing on the measurement of data that depends on the experimental conditions).

  • Controlled Variables:

    • Definition: What is kept the same throughout an experiment to ensure a fair test.
    • Easy Way to Remember: "Controlled = keep it the same".
    • Examples of Controlled Variables:
    • The type of liquid used (such as the specific liquid used to rinse or treat materials).
    • The amount of water used across different test conditions.
    • The specific type of test conducted.

Qualitative Versus Quantitative Observations

  • Qualitative Observations:

    • Definition: Observations that describe qualities or characteristics using descriptive words.
    • Key Characteristics: Involves no numbers; focuses on sensory details such as colour, smell, and texture.
    • Example: Describing clothing as "blue and shiny".

  • Quantitative Observations:

    • Definition: Observations that describe characteristics using numbers or measurements.
    • Key Characteristics: Involves measurable, numerical values and standard scientific units.
    • Examples:
    • Stating that ethanol has a boiling point of 78.3 ∘C78.3\,^{\circ}\text{C}.
    • Stating that an item has a mass of 25 g25\,\text{g} heavy.

  • Mnemonic for Distinguishing Observation Types:

    • Quantitative: Contains the letter "N", which stands for "Number" (data expressed through numerical figures).
    • Qualitative: Associated with "qualities" or words rather than numbers.