Planning an investigation Knowledge-Based Study
Physics topic explanations on Planning an investigation.
Study notes
Every scientific inquiry begins with a clear, testable question about a physical phenomenon. In physics, an effective research question focuses on how changing one physical quantity influences another.
Developing a Scientific Question
A well-defined question avoids vague descriptions and instead identifies observable or measurable properties. For example, rather than asking "How does a parachute work?", a scientist asks: "How does the surface area of a parachute affect its terminal velocity?"
Constructing a Hypothesis
A hypothesis is a proposed, testable explanation or prediction based on existing scientific understanding. It is often framed in a conditional structure:
- Prediction: Stating the expected relationship (for example, if the surface area increases, then the terminal velocity will decrease).
- Scientific Reasoning: Explaining why this outcome is anticipated (greater surface area displaces more air, increasing aerodynamic drag).
To establish a clear cause-and-effect relationship, an experimental investigation must carefully manage all relevant physical parameters, known as variables.
The Three Categories of Variables
- Independent Variable: The physical quantity intentionally altered or set by the experimenter. An experiment should test only one independent variable at a time.
- Dependent Variable: The physical quantity that responds to changes in the independent variable. This is the property being measured or observed.
- Controlled Variables: All other physical factors that could influence the dependent variable. These must be kept constant throughout the investigation to isolate the effect of the independent variable.
Failing to keep controlled variables constant introduces confounding factors, making it impossible to determine whether changes in the dependent variable were truly caused by the independent variable.
A fair test is an experimental procedure where only the independent variable affects the dependent variable, while all other conditions remain strictly controlled.
Selecting Appropriate Equipment
Planning requires selecting instruments with suitable precision, resolution, and range:
- Resolution: The smallest change an instrument can detect (for example, a millimeter ruler versus a vernier caliper).
- Range: The minimum and maximum values the instrument can measure without exceeding its operational limits.
Determining Sample Ranges and Intervals
When planning, specify a realistic range of values for the independent variable. As a standard practice in introductory physics, at least five distinct values with regular intervals should be tested to identify trends reliably (such as linear, inverse, or quadratic relationships).
A robust investigation plan addresses potential sources of error and prioritizes experimental integrity and safety.
Validity and Reliability
- Validity: The degree to which the experiment actually measures what it intends to measure. High validity requires an appropriate experimental design that eliminates systematic bias and properly controls extraneous variables.
- Reliability: The consistency of the results when measurements are repeated under identical conditions. Repeating trials (typically at least three times for each set value of the independent variable) and calculating the mean reduces the impact of random errors and anomalies.
Risk Assessment
Before conducting the experiment, potential physical hazards (such as hot surfaces, suspended masses, sharp edges, or electrical currents) must be identified along with practical precautions to minimize risk to the experimenter and equipment.