SI Units

• SI Units:

  • There are a seemingly endless number of units in Physics
  • These can all be reduced to six base units from which every other unit can be derived
  • These seven units are referred to as the SI Base Units; this is the only system of measurement that is officially used in almost every country around the world
• SI Base Quantities Table:

  
• These base units are then used to derive other common units

  • These units have special names, for example:
  • Newtons, N [kg m / s2]
  • Joules, J [N m]
  • Pascals, Pa [kg / m s2]
• Common Units Table:

  
• Prefixes:

  • Physical quantities can span a huge range of values
  • For example, the diameter of an atom is about 10–10 m (0.0000000001 m), whereas the width of a galaxy may be about 1021 m (1,000,000,000,000,000,000,000 m)
  • This is a difference of 31 powers of ten
• • Each power of ten is defined by a prefix, these are listed in the table below: