0.2 · Preface · Measurement
Can it be measured?
Physical quantities, ratings, scalars and vectors.
SL+HLEasier12 minFree
Hook
How much does a mosquito bite hurt? Ask five friends, get five numbers. Ask five friends the mass of one book, get one. Why?
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Which is a physical quantity?
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"20 m s⁻¹" is…
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What must every physical quantity have?
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A friend says "the concert was 9 out of 10". Is that a physical quantity? Explain.
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Remember earlier lessons
From lesson 0.1
Which unit belongs to energy?
From lesson 0.1
In E = mc², which quantity is squared?
Summary card
Key points
- • Physical quantity: measurable, independent of the person.
- • It needs a number and a unit.
- • Direction is optional: with it, a vector; without, a scalar.
- • Ratings and indices are not physical quantities.
Key terms
- Scalar :
- size and unit only
- Vector :
- size, unit and direction
- Rating / index :
- a personal score
Common errors
- • Saying a scalar has a direction.
- • Writing a number without a unit.
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