People in the united states know that water boils at 212°f. in europe,
people know that water boils at 100°c. is the water in the u. s. different
than the water in europe? what explains the two different temperatures?

They are not two different temperatures.  They are two different
descriptions of the same temperature, using different-size degrees
and different scales.  A lot like "60 miles per hour" and "96.6 kilometers
per hour" ... the same speed. 

In the case of the temperatures, the tags " °F " and " °C " show that the
units are different.  And even though it's not obvious from the descriptions,
they also start counting at different temperatures.

The duration of a photographic flash is related to an rc time constantly