Demonstrate how to convert miles/hour to cm/s by converting 45 mi/h to cm/s.

The best way to do any kind of conversion, but especially
those which switch between the English system and SI (metric system) is to use
conversion factors.

A conversion factor is a fraction which
is created from a mathematical expression of a definition relating measured quantities.
 The fraction is constructed in such a way as to cause the units we wish to eliminate
 will cancel and the units we wish to have left remain.

To
do this conversion we need to have some expressions that relate the quantities to be
changed.  They would be

1.0 miles = 1.6 km which gives two
conversion factors 1.0 mi/1.6 km and 1.6 km/1.0 mi

1.0 km =
1,000 m = 100,000 cm which gives the conversions 1.0km/100,000cm and
100,000cm/1km

1.0 hour = 3,600 s which gives 1.0h/3,600s
and 3,600s/1.0h

To change 45 mile/hour we need to multiply
by the appropriate fractions

45 mi/h X 1.6 km/1.0 mi = 72
km/h

72 km/h X 100,000cm/km = 7,200,000
cm/h

7,200,000 cm/h X 1.0 h/3,600s = 2,000
cm/s

Or we can do it in one string of
calculations:

45 mi/h X 1.6km/mi X100,000 cm/km X 1.0
hr/3,600 s =

2,000 cm/s