The Scientific Method*
Merriam-Webster’s Dictionary defines science in terms of the scientific method,
stating that it is the “knowledge or a system of knowledge … obtained and tested
through scientific method.” Most science textbooks define the scientific method
as a technique in which the researcher defines a problem, makes observations,
generates a hypothesis, designs an experiment, and uses the results to draw
conclusions. The scientific method is often presented in outline form:
1) Research Question: Define the question to be answered
2) Observations: Make observations related to this question
3) Hypothesis: Offer a possible explanation
4) Experiment: Design an experiment to test the validity of the hypothesis
5) Conclusions: Evaluate the hypothesis based on the results
Although many science textbooks imply that there is but one scientific method, in
reality there is no single procedure that scientists follow. Science is a creative
endeavor and scientists are not restricted to a cookbook methodology. Nonethe-less, the scientific method (as commonly presented) is a good tool, but like
any tool, it is best understood through its use.
Key terminology related to "the scientific method"
variable: Something that is capable of changing or varying.
independent variable: A variable that is independent of others, meaning that it
does not change because of dependent variables. In most graphs it is plotted on
the x-axis.
dependent variable: A variable that depends on others (independent variables).
A change in the independent variable may cause a change in the dependent
variable.
quantitative variable: A variable with numerical values (e.g. height, age,
temperature, velocity, distance). Quantitative data are displayed in scatter plots
or histograms.
qualitative variables: A qualitative variables are descriptive, such as color,
category, or population. Qualitative data are best displayed in bar graphs or pie
charts.
control: A subject or object in an experiment that is not involved in the
procedures affecting the rest of the experiment, thus acting as a standard against
which experimental results can be compared.
Herr, Norman. The Sourcebook for Teaching Science. John Wiley Publishers, 2007.
constants: Factors that are held constant during an experiment. To determine
the effect of an independent variable on a dependent variable, all other potential
factors must be held constant.
Observations vs. Inference
Many people confuse observations with inferences. Observations is a record
resulting from the study of an event or object, whereas an inference is a
conclusion that is drawn from evidence based upon observations. Note that
observations do not need to be necessarily visual! We often rely on detection
mechanisms and indirect records, for example in the study of atoms Ernest
Rutherford shot particles through thin foils and detected that some bounced
back. He made an inference using this observation about the structure of atoms
which we use until this day.
Models in Physics
Since the physical world is very complex, physicists often use models. A model
is simplified depiction of reality that is used to isolate a particular feature about a
phenomena. From simple models complexity can be added to explain the more
detailed features, it is the job of a physicists (and engineers and scientists) to
decide what parts are relevant and which can be disregarded or approximated.
This has led to various jokes, including the phrase “consider a spherical cow” to
show how physicists simplify the real world. OK, it's not a great joke, it is the sort
of joke that is only funny to physics students since a common feature of physics
problems is to begin by listing assumptions which are often unrealistic. In reality
a spherical cow would not be such a bad approximation if you want to obtain the
volume occupied by a herb, for example.
The Best Models Make Predictions
There are many models that can explain physical phenomena, but the best
models make predictions. Ptolemy was able to explain the motion of planets
using an Earth-centered model that was incredibly accurate and it stood
unchallenged for more than a thousand years, yet it was an incorrect depiction of
reality! The best models make predictions, Einstein’s General Theory of
Relativity for example, was not widely accepted until one of its predictions was
verified. It predicted that light from a star close to the line of sight of the Sun
would bend due to the Sun’s gravity, this was confirmed during a solar eclipse in
1919.
Herr, Norman. The Sourcebook for Teaching Science. John Wiley Publishers, 2007.