Week 1 - SI Units

What does SI Units stand for?

Système International d’unités — the International System of Units.

Why are SI Units important in science?

• They are the official units for scientific measurement

• Every quantity has a corresponding SI Unit

• It’s important to know what they are

Are all metric units SI Units?

No — the SI system is based on the metric system, but not all metric units are SI Units.

What are the 7 SI base quantities?

• Length 

• Mass

• Time 

• Electrical Current

• Thermodynamic Temperature

• Amount of Substance

• Luminous Intensity

What are the 7 SI base units (symbols)?

• Meter (m)

• Kilogram (kg)

• Second (s)

• Ampere (A) 

• Kelvin (K)

• Mole (mol)

• Candela (cd)

What are prefixes used for in SI Units?

Prefixes are used to represent multipliers or subdivisions of units.

What are the prefixes with their symbols? (Multipliers)

• deca  -  da

• hecto  -  h

• kilo  -  k

• mega  -  M

• giga  -  G

• tera  -  T

• peta  -  P

• exa  -  E

what are the factors/multipliers (large units) of the prefixes?

• da - 10

• h - 100

• k - 1,000 (10³)

• M - 1,000,000 (10⁶)

• G - 10⁹

• T - 10¹²

• P - 10¹⁵

• E - 10¹⁸

What are the prefixes with their symbols? (subdivisions)

• deci  -  d

• centi  -  c

• milli  -  m

• micro  -  μ

• nano  -  n

• pico  -  p

• femto  -  f

• atto  -  a

what are the factors/subtractors (smaller units) of the prefixes?

• d  -   0.1

• c  -  0.01

• m  - 0.001

• μ  -  10⁻⁶

• n  -  10⁻⁹

• p  -  10⁻¹²

• f  -  10⁻¹⁵

• a - 10⁻¹⁸

Example Conversions using SI Prefixes:

• 1 kilometre = 1000 metres

• 1 metre = 100 centimetres

• 1 litre = 1000 millilitres

• 1 kilogram = 1,000,000 milligrams

What is a scalar quantity?

A quantity described by magnitude only (e.g. Distance = 3m).

What is a vector quantity?

A quantity described by both magnitude and direction (e.g. Displacement = 3m Northwest).

What are the rules for scalar arithmetic?

• Add/Subtract: Must have same units

  • If not, convert units first

  • If conversion not possible, they can’t be added

• Multiply/Divide: Multiply or divide magnitudes, and apply the same operation to units

How are vector quantities represented?

• With arrows:

  • Length = magnitude

  • Direction = direction of quantity

• Symbolically as:

  • Arrow over symbol: →s

  • Line over/under: s̅ or s̲

  • In bold type

How do you add/subtract vectors graphically?

• Take each vector in turn (order doesn't matter)

• Place start of one at end of the previous

• Draw a new vector from start of the first to end of the last → Resultant

What is a negative vector?

• Vectors on the same line

• Simply add or subtract magnitudes

• Angle remains the same

• Direction is determined by the larger magnitude

What does Topic 1 Review cover?

• Scientific notation

• Arithmetic with scientific notation

• SI Units

• Prefixes

• Scalar & vector quantities

• Scalar arithmetic

• Vector addition and subtraction