Thinking Like a Physicist: Components of Experimental Design
Vocabulary and insights related to experimental design and the nature of scientific knowledge.
The goal of physics: To describe and explain patterns order in the natural world.
Trend: A predictable change in one or more quantities.
Relationship: A mathematical rule describing a connection between two quantities.
Variable: Quantity that might change during an experiment.
Independent variable: The variable whose value is changed by the experimenter.
Dependent variable: The variable that might be affected by changing the independent variable.
Control variables: Variables whose values are purposely kept constant during an experiment, to avoid possible influences on the dependent variable.
Statement of problem: A description of the possible relationship or trend to be investigated, including the relevant variables, often stated in the form of a question.
Example: How are engine power and vehicle weight related to the acceleration of an automobile?
Claim: A testable prediction of a possible relationship or trend present in a specific situation, never stated in the form of a question.
Example: For automobiles, engine power is directly related to acceleration if other variables are held constant.
Claims must be specific. To say that all objects fall down is not a claim, but to say that all objects near the Earth’s surface accelerate at the same rate is a claim.
Hypothesis: A claim used in scientific inquiry (in an experiment or in research).
The outcome of an experiment will tend to confirm the hypothesis, or to refute it, or the results will be inconclusive. All of these outcomes are useful.
Explanation: A specific statement addressing why something that is observed occurs, possibly including a cause-and-effect relationship or mechanism of change.
Example: Fast moving particles have enough kinetic energy to break free from the surface of a liquid.
Theory: A combination of many related explanations, all shown to be reliable, into a general statement or model.
Example: Atomic theory, our model for the structure of the atom that includes protons, neutrons and electrons, unifies many individual explanations of atomic behavior in chemistry and physics.
Theories are well tested and highly reliable, however, they may be incomplete or require modification over time. Theories are never “proved” or shown to be absolutely true, since doing so would require that every possible related experiment be conceived of and run.
Law: A description of observed events that combines many individual observations into a general rule.
Laws are NOT well-proven theories. Laws are different from theories.