“There are no failed experiments, only failed unimaginative responses to unexpected
occurrences.”
INTRODUCTION:
—B. Shakashiri
The scientific method is a process of investigation designed to acquire new knowledge and construct
theories for explaining and predicting physical phenomena. Systematic observations are used to
formulate hypotheses--proposed ideas meant to tentatively explain phenomena. A sound hypothesis
need not be correct, but it must be testable by experiment. Hypotheses are tested by controlled
experiments and revised when necessary to be consistent with new observations from experiments.
An experiment typically contains at least two variables, quantities that can have more than one value. A
well-designed experiment must be controlled; this means that it measures the effect of one variable
(called the independent variable) on another variable (called the dependent variable) while keeping all
other variables constant (these are the control variables). The independent variable is the quantity in
the experiment that the scientist controls or manipulates; the experimenter then observes the effects
on the dependent variable. If more than one variable changes at a time, it can be difficult to make
conclusions about which variable is influencing the outcome of the experiment. This is the role of
control variables—to eliminate the effects from other quantities so the relationship between
independent and dependent variables can be clearly observed without interference.
The results of experiments must be repeatable to be meaningful. Scientific work is not fully accepted
until it has been verified by other scientists. If reproducible data support a hypothesis, after repeated
experiments a model can be developed to explain the observed phenomenon. As experiments and
observations accumulate over years, decades or even centuries, the model is continually refined and
improved reaching the point of an accepted scientific theory. In this context, a theory is not a hunch or
suspicion. A scientific theory is our best model that serves as a logical framework for representing
reality. It is consistent with generations of experimental observations and is capable of predicting
related phenomena, but must be refined whenever conflicting data appears.
BACKGROUND & BRAINSTORMING:
The basis of this lab starts with a proposed question: "Will ice cubes melt faster when placed in pure
water or in salt water?" To address this question and generate a testable hypothesis, you and your
partner should think about factors that influence the melting of an ice cube. Use your everyday
experiences and knowledge of the world to brainstorm different factors that would affect the rate at
which an ice cube melts. A major part of the scientific method involves asking the right kind of questions
to understand how variables influence each other. You may want to consider the questions below as a
starting point for addressing the larger question above.
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How would you speed up the melting of ice? How would you slow down the melting of ice?
What factors influence melting (pressure, environment, containers, etc.)?
What do you know about the physical properties (like density, buoyancy, boiling point, etc) of
salt water, ice and pure water? How do they differ? How might these physical properties
influence the melting of ice?
Are you aware of any conditions under which salt alone can affect the melting of ice?
LAB INSTRUCTIONS:
During this lab period, the focus will be on the design and execution of experiments to investigate the
proposed question: ”Will ice cubes melt faster when placed in pure water or in salt water?" The goal,
after testing each hypothesis & recording experimental observations, is to establish a model or theory
for explaining the natural phenomena under study. Remember, it is just as valuable to reject an
incorrect hypothesis as it is to confirm a correct hypothesis. Pay careful attention to the variables
involved in each experiment.
1. In the space provided on a scientific record sheet, formulate a hypothesis with your partner to
tentatively explain why ice would melt faster in one liquid or the other. Keep in mind your
hypothesis is not just an expected outcome, but also an explanation for the observed phenomena.
It does not have to be correct initially, but it must be testable and falsifiable, meaning it is capable
of being proved wrong by experiment.
Can you think of multiple, competing scenarios to explain why ice might melt faster in one liquid or another?
Consider Occam’s razor as an initial guide for developing a testable hypothesis.
Occam’s razor: when deciding between multiple hypotheses, the one with the fewest assumptions is usually
the best one to start with. In other words, while a more complicated solution may ultimately prove correct,
in the absence of certainty, the less complicated and fewer the assumptions in a hypothesis, the better.
2. Next you’ll need to come up with a simple experiment to test your hypothesis. You have access to all
of the equipment and supplies available in the laboratory. Before performing the experiment,
describe how you plan to carry out the experiment under Experimental Procedure on the scientific
record sheet.
 Be sure to list the independent variable, the dependent variable & any important control
variables for the experiment, as well. Remember, control variables are factors that are
purposely fixed and unchanging to test how the independent variable affects or influences the
dependent variable without introducing additional complications that would affect the results.
3. Now perform the experiment and record any qualitative observations or quantitative measurements
you collect. It’s always good to have a keen eye for subtle details. Descriptive observations and
comprehensive data collection can only help when trying to interpret the results of an experiment
and reach conclusions.
 For example, pay close attention to the surface of the containers used in the experiment. It may
also be helpful to draw the shapes of the ice cubes as the experiment progresses. If you record
the temperature of the water, where is the temperature recorded? The top of the container?
The bottom? Be specific, consistent & deliberate.
4. Were the results from your first experiment consistent with your hypothesis, or was the hypothesis
proven wrong?
5. A carefully designed experiment should provide new information about the phenomena under
study. Experimental learning in this way provides a tool for refining our understanding of the world.
If necessary, revise your first hypothesis to be consistent with the observations from your first
experiment. Record this update on a new scientific record sheet as Hypothesis #2.
6. Are there any elements or assumptions of your hypothesis that are unsupported? If so, what
experiment could be performed to test these assumptions?
7. Perform additional experiments as needed until you arrive at a working model for explaining the
phenomena of ice melting in pure water versus salt water. The model should be able to explain all of
the details and observations collected from your experiments.
8. A good theory is capable of predicting the outcomes of future experiments. Once you’re confident in
the model you’ve established, ask the instructor to provide you with a new scenario to test its
validity.
a. Write down what you predict as the outcome for this new, but related scenario.
b. Now perform an experiment to verify or refute this expected result. Record the details on
another scientific report sheet. Was the outcome successfully predicted based on your
established theory? If not, what modifications are necessary to make your model consistent
with the latest experiment?