Why do we have 2 high tides and 2 low tides a day?

Whereas semidiurnal tides are observed at the equator at all times, most locations north or south of the equator experiencetwo unequal high tides and twounequal low tides per tidal day; this is called a mixed tide and the difference in height between successive high (or low) tides iscalled the diurnal inequality.