Just a guess but maybe day and night
Days and years.
The repeating phenomena referred to as "day" and "night".
The variation of pressure in liquids and gases in everyday phenomena is referred to in Pascal's Principal and produced by gravity and the Earth's rotation.
What is the earths rotation about
What is the earths rotation about
rotation
the Earths rotation
24 hours rotation
Days & Years.
Days and years.
the presence of day and night proved its rotation
That's "rotation".