Units

 

Why units are important

 

Why are units important?

 

It is important to attach units to a number because without units numbers have no physical meaning.
It is important to attach units to a number to avoid unit mismatch.
It is important to attach units to a number to give the reader a sense of scale.

 

 

 

 

Units of measure

 

A unit of measure is used to define the physical quantity or magnitude of something. There are many measurement systems, but the ones that we are most familiar with are

• SI system
• Metric system
• US customary system

 

The units of measure relevant to dynamics are given in the following table.

 

Metric unit	Symbol	US unit	Symbol	What it measures
Meters	m	Feet	ft	Distance
Kilogram	kg	Slug	slug	Mass
Second	s	Second	s	Time
Newton	N	Pound	lb	Force
Joule	J	British Thermal Unit	BTU	Energy
Watt	W	Horse power	hp	Power

 

SI units

 

All measurement systems, metric and non-metric, are linked through a network of international agreement supporting the International System of Units (SI).