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Unit Conversion Workbench

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About This MicroSim

Most students convert units by remembering a multiplier. That works right up until they meet a conversion nobody taught them, and then it fails completely.

This workbench shows the cancellation method instead. Every conversion is displayed as the original value multiplied by a fraction that equals one, with the units that cancel struck through in red so you can see which unit survives.

Temperature is handled separately and on purpose. The scaling step and the offset step appear on their own lines, because collapsing them into one formula is exactly where students go wrong. The sim also warns about the difference between converting a temperature and converting a change in temperature - a 5 °C rise is a 9 °F rise, not 41 °F.

The Flip the fraction button is the most important control on the screen. It turns the conversion fraction upside down, nothing cancels, and the answer comes out in units like inHg·inHg/hPa which are not a pressure at all. Watching the method fail is what proves that unit cancellation is a check, not a ritual.

How to Use

  • Pick a quantity tab: Temperature, Pressure, Speed or Length.
  • Type a value, or drag the slider. Choose the From and To units.
  • Show me why toggles the full working. Leave it on until the cancellation is obvious.
  • Flip the fraction inverts the conversion factor. Read what happens to the units.
  • Quiz me hides the working and poses a conversion. Answers within 0.1 percent count as correct. A wrong answer reveals the cancellation chain rather than just the number.
  • On the Temperature tab, tick This is a temperature CHANGE to drop the offset step and see why that matters.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://iowerx.github.io/pi-env-monitor/sims/unit-conversion-workbench/main.html"
        height="562px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

6-12

Duration

15-20 minutes

Bloom's Taxonomy Level

Apply (L3)

Prerequisites

  • Multiplying and dividing decimals
  • Reading a fraction as a division

Activities

  1. Exploration (4 min): Start on Pressure with the default 29.92 inHg. Read the chain aloud: "inches of mercury times hectopascals per inch of mercury leaves hectopascals." Then press Flip the fraction and read it aloud again.
  2. Guided practice (6 min): On the Temperature tab, convert 20 °C to °F with the working shown. Now tick the temperature-change box and convert again. Explain in one sentence why the two answers differ.
  3. Assessment (5 min): Use Quiz me five times on the Speed tab. For each wrong answer, find which step of the revealed chain you got wrong.

Assessment

  • Sets up a conversion fraction the right way up without being told which way it goes.
  • Identifies the surviving unit before computing the number.
  • Distinguishes converting a temperature from converting a temperature difference.

References

  1. NIST Special Publication 811, Appendix B: conversion factors - the authoritative factors used in this sim.
  2. Wikipedia: Conversion of units
  3. Wikipedia: Dimensional analysis - the general form of the cancellation method.
  4. NOAA National Weather Service glossary: pressure units - where hPa, mbar and inHg all show up on the same map.