1 / 31

# Units Conversions - PowerPoint PPT Presentation

Units Conversions. Chapter 14. It is absolutely essential to report units with the number answers. Unit History. inch width of your thumb foot originally the length of your foot, now greater yard three feet, from nose to middle finger. Unit History. fathom 6 feet, arm span mile

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about 'Units Conversions' - rafer

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

### Units Conversions

Chapter 14

It is absolutely essential to report units with the number answers.

• inch

• foot

• originally the length of your foot, now greater

• yard

• three feet, from nose to middle finger

• fathom

• 6 feet, arm span

• mile

• 1000 paces, 5280 feet

• furlong

• 220 yards

Example:

T = 77 K

• the quantity of matter in an object

• the measurement of the inertia

• measured in kilograms (kg)

• the force upon an object due to gravity

• Weight = Mass  Acceleration of gravity

Fg = mg

• measured in Newtons (N) in the metric system or pounds (lb) in the British system

• Pound-Mass

• lbm

• One pound-mass weighs 1 pound.

• 1 slug = 32.2 lbm

• Pound-Force

• lbf

• It is the same as a pound (lb).

• 1 lbf = 1 lb

1 lbf = 32.2 lbm ft/s2

Symbol

Length

Mass

time

force

electric current

absolute temperature

luminous intensity

[L]

[M]

[T]

[F]

[A]

[q]

[/]

Dimensions

Fundamental Dimension

time

electric current

absolute temperature

luminous intensity

amount of substance

second (s)

ampere (A)

kelvin (K)

candela (cd)

mole (mol)

Base Units

Base Unit

length [L]

mass [M]

time [T]

electric current [A]

absolute temperature [q]

luminous intensity [l]

amount of substance [n]

meter (m)

kilogram (kg)

second (s)

ampere (A)

kelvin (K)

candela (cd)

mole (mol)

The International System of Units (SI)

What are these things?

• See fundamentalSI.ppt for information about these 'things'

Prefix

Symbol

nano

micro

milli

centi

deci

deka

hecto

kilo

mega

giga

10-9

10-6

10-3

10-2

10-1

10+1

10+2

10+3

10+6

10+9

n

m

m

c

d

da

h

k

M

G

SI Prefixes

Supplementary Dimension

Base Unit

plane angle

solid angle

Base Unit

length [L]

force [F]

time [T]

foot (ft)

pound (lb)

second (sec)

U.S. Customary System of Units (USCS)

Derived Dimension

Unit

Definition

lbf sec2/ft

mass [FT2/L]

slug

F = ma

W = mg

Base Unit

length

mass

force

time

electric charge [Q]

absolute temperature

luminous intensity

amount of substance

foot (ft)

pound (lbm)

pound (lbf)

second (sec)

coulomb (C)

degree Rankine (oR)

candela (cd)

mole (mol)

American Engineering System of Units (AES)

• To convert from foot to meter, multiply by

3.048* E-01

• To convert from meter to foot, multiply by

(3.048* E-01)-1

• Concerning the previous slide, which of the following is true?

a. There are exactly 0.3048 m/ft.

b. There are exactly 0.3048 ft/m.

c. Neither a not b.

• Note, there is a problem when we use the same unit(“pound”, meaning lbf and lbm) to describe two different dimensions.

• Newton's Second Law: F = ma

 1 lbf = 1 lbm ft/s2 ??? NO!!!

• Must have conservation of units.

• Principle of conservation of units:

• units on the left side of an equation must be the same as those on the right side of an equation

• dimensional homogeneity

• Must maintain dimensional homogeneity:

• Now we have lbf = lbf

• See gcderived.ppt for the derivation of gc

• Use a different pairing...

• The force of wind acting on a body can be computed by the formula:

F = 0.00256 Cd V2 A

where: F = wind force in lbf , Cd= drag coefficient (no units), V = wind velocity in miles per hour and A = projected area in ft2

• Is this dimensionally homogeneous?

• What are the dimensions of 0.00256?

Mars Lander (ABC news)

Mars Lander (NASA)

Reality Check...

• You take water from the faucet (80 oF) and bring it to a boil on the stove.

• What is the temperature change in oC?

• What is the initial temperature in oC?

• For the temperature change, the best solution process is to use degree equivalents

• For the temperature value we use temperature conversion:

oC = (5/9)*(80 - 32) = 26.7 oC