Notation, Units, and Rounding Numbers

 

Notation:

 

 

Book

By hand

Scalar

a

a

Vector

a (bold faced)

a or

Units:

 

 

 

SI

 

U.S.

 

Mass

M

kilogram

kg

slug

 

Length

L

meter

m

feet

ft

Force

F

Newton

N

pound

lb

Time

T

second

s

second

sec

 

Relation between units is based on the equation F=ma:

1 N = (1 kg) (1 m/s2)

1 lb= (1 slug) (1 ft/sec2 )

 

Example of calculating mass in U.S. system: The mass, m, of a particle which weighs W=10 lb and is in a gravitational field of with an acceleration of gravity g=32.2 ft/sec2 is

 

Unit conversion:

 

l lb

=

4.4482 N

1 slug

=

14.5938 kg

1 ft

=

0.3048 m

1 ft

=

12 in

1 mile

=

5,280 ft

1 kip

=

1,000 lb

1 ton

=

2,000 lb

 

Rounding numbers:

Round your final answers to 3 significant figures

 

Check equations by checking that all terms in an equation have the same dimensions

 

 


Mehrdad Negahban and the University of Nebraska, 1999-2000.

All rights reserved

Copy and distribute freely for personal use only

 

Department of Engineering Mechanics, University of Nebraska, Lincoln, NE 68588-0526