From: Di <diane.canavan@ozemail.com.au>
To: Teacher2Teacher Public Discussion
Date: 2006100610:18:16
Subject: Re: Graphing

Judy, you didn't state the context of the activity.  Was it a science
activity to investigate speed or momentum, or a maths activity to
build up graphing skills?  Either way, it makes no difference to your
basic question about discrete vs continuous data, but may make a
difference to whether a bar graph is the best option.
In doing this experiment, your children are investigating the effect
of the speed of the marble on the movement of the cup.  To create
different speeds the marble is released from different heights on the
ramp.  The distance up the ramp determines the speed.  In the activity
distances of 10, 15, 20 were chosen for data collection.  You could
have chosen any distances at all along the ramp to investigate the
relationship.  You would expect the value for 12 to fall between the
values for 10 and 15.  You could have measured from  12.5 and found
the value to fall between that for 12 and 13.  In other words, there
is a direct relationship between the distance along the ramp and how
far the cup moves.  The data is therefore continuous.  I would draw a
dot plot and line of best fit (connect the dots as well as you can
with a smooth line/curve).  
If the primary purpose of the activity was to learn to investigate,
measure, record and predict, I would accept the bar graph.  If you
wanted to teach the conventions of graphing, the bar graph is not the
best choice.

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