Difference between 'Uhr' and 'Stunde'

What is the difference between Uhr and Stunde?

1. is used when telling the time, indicating a point in time, for example:

Es ist jetzt 12 Uhr.

2. a watch or clock, for example:

Die Uhr ist kaputt.

1. means a time period of 60 minutes, for example:

Sechzig Minuten sind eine Stunde.

2. means a school lesson, for example:

In der ersten Stunde haben wir Mathe.

See words in context to better understand their meaning and use.