Practicing Scientific Processes
Handbook : Practicing Scientific Processes
Scientists use an orderly approach to learn new information and to solve problems.
The methods scientists may use include observing to form a hypothesis, designing
an experiment to test a hypothesis, separating and controlling variables, and
Operational definitions define an object by showing how it functions, works, or
behaves. Such definitions are written in terms of how an object works or how it
can be used; that is, what its job or purpose is. Some operational definitions
explain how an object, such as the car in Figure 15, can be used.
- A car
is a vehicle that can move things from one place to another. Or such a definition
may explain how an object works.
- A car
is a vehicle that can move from place to place.
A hypothesis is a prediction, based on observation, that can be tested. Hypotheses
are often stated as if-and-then statements. A hypothesis needs to be testable.
a scientist has observed in Figure 16 that plants that are fertilized grow
taller than plants that are not. A scientist may form a hypothesis that says:
If plants are fertilized, then they will grow taller. This hypothesis can be tested
by an experiment.
an Experiment to Test a Hypothesis
procedural steps. Once you have stated a hypothesis, you probably want
to find out whether or not it explains an event or observation. In order to test
a hypothesis, you must perform an experiment. When conducting an experiment, it
is best to begin by writing out a procedure. A procedure is the plan that you
follow in your experiment. A procedure tells you what materials to use and how
to use them. After following the procedure, data are obtained. From this data,
you can then draw a conclusion and make a statement about your results.
conclusion you draw from the data supports your hypothesis, then you can say that
your hypothesis is reliable. Reliable means that you can trust your conclusion.
If it did not support your hypothesis, then you would have to make new observations
and state a new hypothesis-just make sure that it is one that you can test.
Suppose you hypothesize that a houseplant will grow better if watered with bottled
water than with tap water.
out how to conduct an experiment to test the hypothesis: If a plant is watered
with bottled water, then it will grow better and look healthier. An example procedure
is seen in Figure 17. The data generated from this procedure are shown
in Figure 18. The data show that the plant grew the same amount each month
regardless of the type of water used. This conclusion does not support the original
Separating and Controlling Variables
In any experiment, it is important to keep everything the same except for the
item you are testing. The one factor that you change is called the independent
variable. The independent variable in the experiment on the previous page was
the type of water. The factor that changes as a result of the independent variable
is called the dependent variable. The dependent variable in the experiment was
the plant height. Always make sure that there is only one independent variable.
If you have more than one, you will not know what caused the changes you observe
in the independent variable. Many experiments have a control. A control is a treatment
or an experiment that you can compare with the results of your test groups.
experiment with the plants, you made everything the same except the type of water
being used. The soil, the amount of water given, the amount of light, and the
temperature of the room should remain the same throughout the entire experiment.
By doing so, you made sure that at the end of the experiment, any differences
were the result of the type of water being used bottled or tap. The type
of water was the independent factor, and the height of the plant was the dependent
The word interpret means "to explain the meaning of something." Look at the problem
being explored in the plant experiment. and find out what the data show. When
you looked at the data you collected, you were checking to see if the variable
had an effect. You were looking for an explanation. If there are differences in
the data, the variable being tested may have had an effect. If there is no difference
between the control and the test groups, the variable being tested apparently
has had no effect.
at Figure 18, which shows the results of this experiment. In this example,
the use of tap water to water the plant was the control, while watering the plant
with bottled water was the test. Data showed no difference in the amount of plant
growth over a one-month period.
In the experiment described on these pages, measurements were taken so that at
the end of the experiment, you had concrete numbers to interpret. Not every experiment
that you do will give you data in the form of numbers. Sometimes data will be
in the form of a description. At the end of a chemistry experiment, you might
have noted that one solution turned yellow when and another remained treated with
a particular chemical, clear when treated with the same chemical. Data, therefore,
are stated in different forms for different types of scientific experiments. Are
all experiments alike? Keep in mind as you perform experiments in science that
not every experiment makes use of all of the parts that have been described on
these pages. For some situations, it may be difficult to design an experiment
that will always have a control. Other experiments are complex enough that it
may be hard to have only one dependent variable. Scientists use many variations
in their methods of performing experiments. The skills in this handbook are here
for you to use and practice. In real situations, their uses will vary.