0.5 · Preface · Tools: derived units
Derived units
Area, speed, acceleration, force and pressure, all built from base units.
SL+HLMedium12 minFree
Hook
A ruler gives metres. How do you measure how big a tabletop is, or how fast a car goes? No new unit needed: just combine the ones you have.
The idea
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The SI unit of area is…
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An object accelerates at 5 m s⁻². This means…
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The newton in base units is…
Apply
A 3 kg trolley accelerates at 4 m s⁻². Find the force on it and give the unit in two ways.
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Remember earlier lessons
From lesson 0.4
kilo means…
From lesson 0.3
Which is NOT a base unit?
Summary card
Key points
- • Derived units combine base units.
- • Area m², volume m³, speed m s⁻¹, acceleration m s⁻².
- • Force: N = kg m s⁻². Pressure: Pa = N m⁻².
Formulas
- F = ma
- p = F / A
Key terms
- Newton (N) :
- the unit of force, kg m s⁻²
- Pascal (Pa) :
- the unit of pressure, N m⁻²
Common errors
- • Writing m for an area.
- • Confusing the newton (kg m s⁻²) with the joule (kg m² s⁻²).
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