13
Sketch: Not needed
Data: Δ v =20 m/s – 0 m/s = 20 m/sec, t = 10 s, wanted: a?
Working equation:
a
a
Substitute:
v
t
v f vi
t
20 m / s 0m / sec
2m / s2
10 s
1.8 Unit Conversion
To a scientist or a student studying science, unit conversion is extremely important. Therefore, the
students must be able to convert back and forth between metric (SI) units.
Unit conversion is based on the availability of conversion factors. Table (1.3) shows a few common
conversion factors.
Table (1.3) some useful conversion factors
1 km = 103 m
1m = 10-3 km
1 m = 102 cm
1 cm = 10-2 m
1 cm = 10 mm
1 mm = 10-1 cm
1 kg = 103 g
1g = 10-3 kg
1 day = 24 hr
1 cm3= 10-6 m3
1 min = 60 sec
1 y = 365 d
The process of unit conversion is based on replacing an unwanted unit by a wanted unit; it can be
summarized as follows
Write down the given number with its unwanted unit
Multiply this by a ratio of 1. The ratio is written from a given conversion factor and it
consists of two units, the unwanted unit and the wanted unit. Remember that you need to
cancel the unwanted unit