Year 9 Revision Variables

Revision: Variables, Means, and Graphs

This guide is essential for all scientific subjects.

Variables

  • Definition: Variables are elements that can change in an experiment.

  • Types of Variables:

    • Independent Variable: The variable that is intentionally changed or manipulated.

    • Dependent Variable: The variable that is being measured or tested in the experiment.

    • Control Variables: These are the factors that must remain constant throughout the experiment to ensure valid results.

Example: Water Rocket Experiment

  • Independent Variable: Angle of the slope (what is changed).

  • Dependent Variable: Distance traveled by the water rocket (what is measured).

  • Control Variable: Amount of water in the rocket (kept the same to avoid affecting the results).

Task 1: Identifying Variables

Decide the type of variable for the following experiments:

  1. Ball Drop Experiment:

    • Independent Variable: Height from which the ball is dropped.

    • Dependent Variable: Height that the ball bounces.

    • Control Variable: Type of ball or surface it bounces on.

  2. Current and Temperature Experiment:

    • Independent Variable: Current flowing in the wire.

    • Dependent Variable: Temperature of the wire.

    • Control Variable: Type of wire used.

  3. Lichen Growth Experiment:

    • Independent Variable: Direction (North, South, East, West).

    • Dependent Variable: Amount of lichen growth.

    • Control Variable: Type of tree or environmental conditions.

  4. Magnesium Oxide Experiment:

    • Independent Variable: Amount of magnesium used.

    • Dependent Variable: Amount of magnesium oxide produced.

    • Control Variable: Temperature or reaction environment.

Choosing the Right Type of Graph

  • Types of Graphs:

    • Line Graph: Used for continuous variables (two sets of numbers).

    • Bar Chart: Used for categoric variables (words and numbers).

  • Graph Requirements:

    • Fully labelled (axes, title).

    • Regular scales should be used for consistency.

Series Circuit Note

  • In a series circuit, the potential difference (p.d.) drops across each component and adds up to the total supply voltage.

Task 2: Graph Requirements for Experiments

Experiment Description

Type of Graph Needed

Why This Graph is Needed

Measuring maximum speed of five different shark species

Line Graph

To show continuous data points over time.

Measuring barnacle numbers on a cliff face

Bar Chart

To compare different categories of locations.

Discovering dates for different metals' discovery

Bar Chart

To categorize data over time.

Speed of a toy car vs. inclination angle

Line Graph

To track the continuous relationship.

Finding a Mean

  • Purpose: Repeating experiments helps verify results' reliability and allows calculation of the mean.

  • Calculation Steps:

    1. Add all results together.

    2. Divide the total by the number of results.

Example: Ruler Bending Experiment

  • Results: 11mm, 12mm, 10mm, 12mm, 10mm.

  • Total = 11 + 12 + 10 + 12 + 10 = 55mm

  • Mean = 55 ÷ 5 = 11mm

  • Note: If one result is significantly different from others, it may be untrustworthy and excluded from the mean calculation.

Task 3: Calculate Means

  1. Radioactive Material in Chernobyl:

    • Results: 10mg, 8mg, 12mg, 12mg, 9mg.

    • Mean = (10+8+12+12+9) ÷ 5 = 10.2 mg

  2. What does mg mean?

    • mg = milligrams (a unit of mass).

  3. Mean Size of Lichens:

    • Results: 4.5cm, 6.2cm, 5.1cm, 6.4cm, 6.4cm, 8.1cm, 8.4cm, 4.9cm, 6.2cm, 7.3cm.

    • Mean = (4.5 + 6.2 + 5.1 + 6.4 + 6.4 + 8.1 + 8.4 + 4.9 + 6.2 + 7.3) ÷ 10 = 6.21 cm

  4. Dissolving Magnesium Strip in Nitric Acid:

    • Results: 45 seconds, 48 seconds, 44 seconds, 5 seconds, 46 seconds.

    • Mean = (45 + 48 + 44 + 5 + 46) ÷ 5 = 37.6 seconds.