Converting the masses

We needed to work on this with GCSE resit groups:

20130415 - pic1

Dry, dry topic. Maybe, but here’s what I did, and then what I’m gonna do next time.

Step 1
Throw this up:

20130415 - C Pool Metric Imperial_2

Step 2
Give them random shhhtuff to measure


Step 3
Collect results:
20130415 - C Pool Metric Imperial_3

Step 4
Graph it in Desmos:

20130415 - pic3

Step 5
Make an estimate of the conversion factor

20130415 - pic4

Step 6
Ask Google if we were right
20130415 - pic2

Step 7
Repeat for other data

Step 8
Try some conversions using the correct ratios.

Two (large) issues occurred

  • Students can’t measure in inches
  • Students mis-scaled their axes

So, the second is worrying; axis starting at one (or two!?) and axes with inconsistent spacing make it all but impossible to predict from the graph and gave some students the conversion that 1″ is negative cm or other such nonsense. I think that this realisation MAY have have had an impact, as the next batch of graphs they drew, I saw no similar issues. However; there students should be able to draw correctly scaled axes. Starter perhaps for tomorrow’s lesson?

The first is less worrying for the exam content (they will never be asked to measure in inches) but more worrying in terms of LIFE. I see the start of next lesson also including reading scales…

So what will I do differently next time?

    • Start the lesson off with scale reading
    • Give them the axes – ideally they’d use graphic calcs and lin reg it and such, but that’s waaay beyond what these students need and several lessons to get them to use the calculators!
    • Give them more opportunity to measure. I’m thinking scales in the classroom and maybe Google Earth to measure distances? – I feel stations coming on…

Next year…

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4 Responses to Converting the masses

  1. Fawn Nguyen says:

    Really really good, Nik. You use inches too where you live? 🙂 Graphing the relationship using Desmos is a total winner. That said, do they need to graph this by hand at all? Might be a good opportunity to reinforce graphing skills, but maybe that’s not the focus of this lesson?

    I love that the kids start with measuring random stuff though, so not sure if you’d want to change that to “scale reading.” (And I don’t know yet what you have in mind for this.) Good to know our American kids aren’t the only ones who mis-scale the axes! Step 7 is blocked out here at my school desktop.

    I’d replicate what you have here for measuring drying weights and liquids also. Fantastic lesson, Nik, I have to save it for next year. (Speaking of bookmarking and saving lessons from online, another monumental task for this summer.)

    • nik_d_maths says:

      😀 We don’t use inches for anything really – but we have to teach the conversions. I guess the only thing you regularly see inches used for is screen dimensions [quick thought – inch measurement vs. square cm area??]. It was tough finding enough rulers with both units on!

      I think you’re right about not diluting the hook – I think maybe it would have been better to just pull the whole class up on it when a couple made that error.

      I would love to get them to do the graphing themselves in Desmos, BUT right now I’m the only person who can… (Only one with Chrome… the graphing, it is mine!). Drawing the lines in Desmos has the advantage of making them think more about gradients, vs. plotting odd points on often poorly thought out scales. Hmmmm.

      Step 7 is not that exciting, just a sheet of data to graph.

      Mass measurements, volumes and Google Earth distances and areas are totally something I want to do next year.

      Thanks Fawn!

  2. Fawn Nguyen says:

    I forgot to say THANK YOU!!!!!!!! So, thank you, Nik.

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