CECsci.186


TITLE:    LOOKING AT VARIABLES

AUTHOR:   Gary L. Wiggins, Cascade Elementary
          East Wenatchee, Washington

GRADE LEVEL:   4 - 6

OVERVIEW:  This lesson, using sugar cubes and water,
exposes students to the variables
(manipulated/independent, responding/dependent) found
in scientific experimentation.  Students will use
controls to be sure they are testing only certain
independent variables.  Students will be using good
experimental design as they test each of their guesses
(hypotheses).

PURPOSE:  The purpose of the lesson is to show students
that, when doing experiments, scientists must be sure
that the experiments are reliable and the results are
valid.  They must eliminate or test all variables that
can effect the results of an experiment?

OBJECTIVE(s):
1    Students should be able to understand the
     following terms:  reliable, valid, hypothesis,
     independent variable, dependent variable, control.
2    The students should be able to use experimental
     design--Predict, Test, Observe, Hypothesize.
3    Students should become critical observers of other
     experiments in terms of what is necessary for an
     experiment to be reliable and the results to be
     valid.

RESOURCES/MATERIALS:  Lots of sugar cubes, hammer for
smashing cubes, 4 plastic party glasses for each group,
paper towels or sponges, variety of spoon sizes,
thermometers, rulers, stopwatches, etc.

ACTIVITIES AND PROCEDURES:
     First, each group of three should be given 4 sugar
cubes, 4 clear plastic party glasses, and 2 spoons.
Explain that each group will dissolve each cube of
sugar in the glasses.  In one glass there will be a
cube and water, one will have a cube, spoon (stirred),
and water, another will have a smashed cube and water,
and the last will have a smashed cube, spoon
(stirring), and water.  "Students predict which
container will have the fastest rate of dissolving."
Students need to be reminded to have a way to start all
stations together or time each (stopwatch)
individually.  Let them at it!!
     Secondly, now that a mess has been made, and
everyone is wondering if anything can possibly be
learned from this activity, clean up and prepare for
processing, instruction, and brainstorming.  Talk about
predictions (it's okay to have wrong
predictions--happens all the time), graph the results
of the experiments.  Are there different results?  Were
all the methods of experimentation the same?  Can we
hypothesize using our data?  Was every group's water
the same temperature (even within the group)?  Did
everyone stir at the same rate?  Was there equal
amounts of water in each glass?  Could any of this make
a difference?
     Now is the time for instruction regarding
reliability, validity, independent and dependent
variables, and controls.
     Brainstorm a number of manipulated/independent
variables that could have had an effect upon the
results of our experiment (the rate of dissolution).
Put suggestions on a chart and have the groups test
each variable against a control to see if it has any
effect on the rate of dissolving.  This may take more
that one day.  Teacher's job is to make sure supplies
are available.  The chart may look like this:

Independent  |Prediction  |Exp. Notes   |Observation
 Variable
-------------|------------|--------------|----------
spoon size   |            |              |
-------------|------------|--------------|----------
  amount of  |            |              |
    water    |            |              |
-------------|------------|--------------|----------
  stirring   |            |              |
   speed     |            |              |
-------------|------------|--------------|----------
    water    |            |              |
 temperature |            |              |
-------------|------------|--------------|----------
placement of |            |              |
  spoon      |            |              |
-------------|------------|--------------|----------
   extra     |            |              |
 agitation   |            |              |
-------------|------------|--------------|----------
 old vs.     |            |              |
new cubes    |            |              |
-------------|------------|--------------|----------
different    |            |              |
solvents     |            |              |
-------------|------------|--------------|----------
             |            |              |
-------------|------------|--------------|----------
             |            |              |
-------------|------------|--------------|----------

After the experiments have been completed, data may be
compiled from the groups.  If there is a question of
validity, go back and re-test.  Again, process the
activity using the important vocabulary words.

TYING IT ALL TOGETHER:  Again, alert the students to
the sometimes enormous amount of variables that can
have an effect upon the many experiments which
scientists perform.  We must strive for "pure"
experiments for reliability and validity. Using the
data from the preceding experiments, have the groups
develop the "ultimate (fastest) sugar dissolving
system.