Another example of Units, with conversions

•1 light-year
= c ´ t (where c is
the speed of light and t is one year)

= 3.0 ´ 108 m/s ´ 365 days

= 1.1 ´ 1011 (m ´ days /s)

= 3.0 ´ 108 m/s ´ 365 days

= 1.1 ´ 1011 (m ´ days /s)

•but we know light-years is a distance and must have
“dimensions” of distance. We should have units of just meters. The fact that we have this extra (days/s) means we have left something out.

•If we multiply by
(24 hr/day ´ 60 min/hr ´ 60 sec/min) the
units will work out right and so
will the numerical answer

•

= 1.1 ´ 1011 ´ 24 ´ 60 ´ 60 m

= 9.5 ´ 1015 m

= 9.5 ´ 1012 km

= 1.1 ´ 1011 ´ 24 ´ 60 ´ 60 m

= 9.5 ´ 1015 m

= 9.5 ´ 1012 km