Distribution Graphs…

When 8R & 8L have done their power experiment, we can plot a distribution curve showing how much variation there is in power between members of Y8.

Normal distribution describes the range of outcomes when collecting data during experiments. Some of the numbers will be larger than the average and some will be below average but most will fit into a region around the average answer. If enough data is plotted, you get a distribution curve shaped like this.

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For example, a couple of years ago I combined all the data from our ‘Who Is The Most Powerful’ practical and plotted the ranges for all the boys from 2005 to 2007. Some produced exceptionally high values, a few very low ones but most boys were close to the average for the year. In total there were 112 results, which I thought was enough to give a reasonable distribution. I broke the results up into ranges and then counted how many boys fitted into each range. Then I plotted them as a bar graph.

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The data matches a normal distribution fairly closely.

For many years DCP and CS used to do a practical counting and comparing the prickles on the two varieties of holly trees that grow at Summer Fields – plain & variegated. The boys then plotted the data on a graph like the one below.

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Although neither of these graphs is an exact fit for the ideal curve shown at the top, they do indicate the trend and may help to explain the idea. This sort of distribution is what you would expect when measuring most natural phenomena. If you collect more data you would produce a graph that is more normal. This is why large sample sizes and good experimental technique are so important – it is easy to skew your results with poor or insufficient data.

Questions…

1. What form or energy were you generating as you ran up the stairs?
2. What is the SI unit of energy?
3. How did we calculate how much energy you produced?
4. How do you calculate power?
5. When we did the power practical, what was the most significant factor that determined how much power you generated?
6. Why do holly leaves have prickles?
7. Which kind of holly has the most prickles on average?
8. What does variegated mean?