Experiment Variables and Methods

Variables in Experiments

  • In an experiment, you might measure variables such as a, b, c, d, and e.
  • Typically, you'll consider two relationships out of a possible five.

Types of Variables

  • Independent Variable (IV):
    • The variable you deliberately change (e.g., level one, level two, this year, last year).
    • Usually plotted on the x-axis.
  • Dependent Variable (DV):
    • The variable that changes because you changed the independent variable.
Example Scenario: Ball Rolling Down a Ramp
  • IV: Height/angle/slope of the ramp.
  • DV: How fast the ball rolls.
Advanced Considerations
  • In later studies (Year 12/13), you might encounter multiple independent variables.

Controlled Variables (CV) / Fixed Variables

  • Things you keep the same to ensure a fair test.
  • Kept constant so they don't affect the results.
Example: Ramp Experiment Revisited
  • Problem: Using a golf ball on one ramp and a tennis ball on another introduces an uncontrolled variable.
  • Problem: Having a wood surface on one ramp and a covered surface on another introduces an uncontrolled variable.

Method

  • A step-by-step account of what you do in the experiment.
  • The goal is to enable someone unfamiliar with the experiment to replicate it.
  • Provide enough detail so that a "non-complete stranger" can understand and reproduce the experiment.

Importance of Detail

  • Avoid vague instructions like "grab the gear."
  • Specify what gear to grab and how to set it up.
  • Include diagrams if necessary.
  • Review the method as if you were someone else to ensure clarity.

Instrumentation and Measurement

  • In science, it's essential to record data.
  • "The difference between messing around and science is in science, you write things down."
  • Use instruments to measure things.
  • Start with your eyes, then use instruments.

Tools for Measurement

  • Examples: Rulers, stopwatches, etc.
Using a Ruler Properly
  • Start measurements from zero.
  • Example: Measuring a marker and finding it to be roughly 12.6 cm.
Zero Error
  • Definition: An error caused by the instrument not starting at zero.
  • Example: Stopwatch not reset to zero before timing.
  • Example: Bathroom scale needs to be at zero before use, press tare to get to 0.
Avoiding Zero Error
  • Reset the instrument to zero before use.
  • If you cannot avoid it, measure the error and subtract it from your results.
Parallax Error
  • Occurs when reading measurements from an angle rather than straight on.
  • Example: Reading a meniscus in a cylinder.
    • Don't read from below or above; read at eye level.

Measuring with a Ruler

  • Keep eye level. Do not measure at an angle.
  • Make sure to read at a 90 degree angle to the device.

Errors in Measurement

  • Zero Error: Reset the measuring device.
  • Parallax: View the measuring device at 90 degrees.

Placement

  • Watch the finish line closely, to avoid parallax error.

Human Error

  • Unavoidable but should be minimized.
  • Example: Reaction time when using a stopwatch.
    • Delay between brain processing and hand movement.
    • The device may be perfect, but the human using it introduces error.

Experiment: Pendulum Period

  • Objective: Measure the period (time for one complete swing) of a pendulum.
  • Consider the swing is from one position back to the same position.

Variables

  • IV: Length of the pendulum string.
  • DV: Period of the pendulum.

Accuracy

  • One swing might be too small to measure accurately.
  • Instead: Time 10 swings and divide by 10 to improve accuracy.

Using the Stopwatch

  • Right button: Start/Stop
  • Middle button: Reset
Understanding the Display
  • Left number: Minutes
  • Middle number: Centiseconds
  • Right number: Seconds

Pendulum Setup

  • Need to use the longer one not shorter.
Creating an Even Swing
  • Tie the string so that the pendulum can swing evenly on both sides.

Planning the Experiment

  • Determine the range of the independent variable (length).
  • Consider the number of values you'll test, balancing it with time constraints.

Repeats

  • Don't just time one set of swings one time.
  • Do repeats.
  • Aim for at least three repeats to ensure reliable results.
  • (9=3).(\sqrt{9} = 3).