To: Teacher2Teacher Public Discussion
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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