Units of Measurement Commonly used Units of Measurement Length - - PowerPoint PPT Presentation

Units of Measurement

 Commonly used Units of Measurement  Engineering commonly uses 2 different systems of units

 SI (System Internation) or Metric  US Customary or English

• Length
• Time
• Mass
• Force

Units of Measurement

SI US, English Length m - meters ft – feet Time s – seconds s – seconds Mass kg – kilograms slug Force N - newton lb – pounds

SI – System International

 Force – Newton

A body of mass of 1 kg has a weight of 9.81 N

mg W 

2

81 . 9 1 s m kg 

2

81 . 9 s m kg  N 81 . 9 

2

1 s m kg N 

2

81 . 9 s m g 

By definition:

SI Prefixes

Symbol Prefix Multiplication Factor G giga 1,000,000,000 109 M mega 1,000,000 106 k kilo 1,000 103 m milli 0.001 10-3 µ micro 0.000001 10-6 n nano 0.000000001 10-9

US Customary - English

 Mass – Slug

A body of weight 32.2 lb has a mass of 1 slug

g W m 

2

2 . 32 2 . 32 s ft lb 

ft s lb Slug

2



2

2 . 32 s ft g 

ft s lb

2

1 

By definition:

Slug 1 

Significant Figures

 Generally 3 or 4 appropriate on final answer  Keep intermediate calculations in calculator  Round final answer  Examples:

4.78 47.8 0.478 4780 4.78*103