1. Unit Conversion

2. Matching Units Conversion between units must be of the same type.
Length conversion:
1 in = 2.54 cm
Time conversion:
1 hr = 3.6 x 103 s
No conversion between different types of units.
1 in is not equivalent to some seconds

3. Conversion Factors
A value is converted by applying the ratio of the conversion factors.
How many inches in 50. cm?
50. cm (1 in / 2.54 cm) = (50. / 2.54) in = 20. in
Many conversion factors use scientific notation.
How many seconds in a year?
1 yr (365 d/yr) (24 hr/d) (3.6 x 103 s/hr) = x 103 s = 3.15 x 107 s

4. Orders of Magnitude What is bigger? A) DeKalb compared to you.
B) The earth compared to DeKalb.
C) Our galaxy compared to the solar system.
D) Universe compared to our galaxy.

5. Human Lengths You Lecture Hall Faraday West NIU
5’9” = 1.75 m = 2 x 100 m
14 m = 1.4 x 101 m
80 m = 0.8 x 102 m
2000 m = 2.0 x 103 m = 2.0 km

6. Map Lengths
Huskie Stadium
DeKalb City
DeKalb County
Illinois
United States
100 m = 102 m
5000 m = 5 km = 5 x 103 m
30,000 m = 30 km = 3 x 104 m
400 km = 4 x 105 m
5000 km = 5 x 106 m = 5 Mm
mapquest uses scaling factors, about two steps per order of magnitude

7. Planetary Lengths Earth Earth and Moon Earth to the Sun
13,000 km = 1.3 x 107 m
384,000 km = 4 x 108 m
150,000,000 km = 1.5 x 1011 m
This is 1 Astronomical Unit (1 AU)

8. Solar-system Lengths Earth to the Sun Solar System 1 AU = 1.5 x 1011 m
8 light-minutes
500 AU = 0.8 x 1014 m
3 light-days

9. Galactic Lengths Nearest Star Milky Way Universe
300,000 AU = 4 x 1016 m
4.3 light-years = 4.3 ly
100,000 ly = 1021 m
15,000,000,000 ly = 1.5 x 1026 m

10. How Big? A) DeKalb compared to you. (103)
B) The earth compared to DeKalb. (103)
C) Our galaxy compared to the solar system. (107)
D) Universe compared to our galaxy. (105)
next