What fraction of an hour is a second?

To express a second as a fraction of an hour, let's look at standard time conversions:
* $1\text{hour}=60\text{minutes}$
* $1\text{minute}=60\text{seconds}$

Multiplying these gives total seconds in one hour:

$$1\text{hour}=60\times 60\text{seconds}=3600\text{seconds}$$

Therefore, $1\text{second}=\frac{1}{3600}\text{of an hour}$.