significant figures

In our discussions yesterday, one of the things that cropped up was that we need to revise the material covered before the summer holidays.  I thought I would make a start on this by looking at significant figures.  

You might have heard me referring to “calculator vomit” in class.  This is an expression I use whenever people simply write down the answer provided by their calculator, without thinking about whether or not the number of decimal places reported is appropriate.  In Physics, we can avoid “calculator vomit” by using significant figures.  I’ve provided some links below to direct you to sites that explain what significant figures are and how to use them.


If you’ve read through some of those pages and feel that you are ready for a test, you can try your luck at

Note: these links might also be useful for AH pupils analysing their investigation data.

0 thoughts on “significant figures

  1. A little activity to remind them might be to measure the three dimensions of, say, a table. Write these three lengths down with the correct measurement uncertainty. Now calculate the volume of the box which would exactly fit the table.

    They should see, physically, what a reasonable statement of the volume should be.

    Example: using a metre stick marked in mm, a table is 1.250 ± 0.005m by 0.621 ± 0.005m by 1.402 ± 0.005m. On my calculator, that’s 1.0883025 cubic metres.

    What volume is represented by the 5? the 2? What difference in the answer if the last measurement was 1.403 ± 0.005m? I get a volume of 1.0890787500000001 cubic metres this time.

    You can abstract from there but hopefully they will consider the physical implication of the numbers they write down.

    I always say that the calculator is never to be trusted: every answer it produces always requires an interpretation.

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