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Numbers & Ratios — Teacher Instructional Notes
Dimensional Analysis
Teaching focus
- Also known as "Unit Factor Method" or "Factor-Label Method".
- Core Logic: Multiplying by 1 doesn't change the value, only the unit.
- Structure: (Given Unit) × (Desired Unit / Given Unit) = Desired Unit.
- Essential for Stoichiometry in Unit B.
Demonstrations and analogies
Measurement Train Tracks:
- Start with something fun: "How many seconds old are you?"
- Draw horizontal "train tracks". Place 16 years.
- Next block: 365 days / 1 year. Years cancel.
- Next block: 24 hours / 1 day. Days cancel.
- Keep going until seconds. It visually shows units cancelling like numbers.
Common misconceptions
- Setting up the ratio upside down (units don't cancel).
- Trying to do it all in their head (works for simple stuff, fails for moles).
- Forgetting that some conversions are squared/cubed (e.g., cm² to m²).
Teacher Action
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