Caption: Unit conversion.
Unit conversions often seem difficult, but they are simple with the general approach of using factors of unity (i.e., conversion factors) which are factors that have value 1. The key point is that multiplication by a factor of unity does NOT change the value of thing it multiplies because the factor of unity has value 1.
One does unit conversions by multiplying numbers by factors of unity and treating units as algebraic symbols (or algebraic variables) which is correct since units are algebraic symbols among other things.
For example, say you wanted to convert 10 km into meters. Well 1 km = 10**3 m. Therefore, the appropriate factors of unity is 1 = (10**3 m/1 km). Thus
