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Units, prefixes and vectors
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Physics answers only make sense with the right units. Prefixes and vectors come up in almost every topic.
SI units
Base units include the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K) and mole (mol).
Other units are built from these. Speed is m/s and force is the newton (N).
Other units are built from these. Speed is m/s and force is the newton (N).
Prefixes
Prefixes multiply a unit.
Scalars and vectors
A scalar has size only: distance, speed, mass, energy, time.
A vector has size and direction: displacement, velocity, acceleration, force, momentum.
A vector has size and direction: displacement, velocity, acceleration, force, momentum.
Convert 350 mA into amps.
- milli means × 10-3, so divide by 1000.
- 350 ÷ 1000 = 0.35
Answer: 0.35 A
Use SI units in equations. Kilo is 1000, milli is one thousandth, micro is one millionth. Vectors have direction; scalars do not.
The interactive lesson includes the diagrams for this topic.
Check you have got it
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