The Cause of Tides

    In recent years, two questions in particular have not been asked at this level. They are:-

1.    Explain the cause of twice-a-day (semi-diurnal) tides, &

2.    Explain the cause of once-a-day (diurnal) tides.

    This omission could be because these questions are not in the OOW syllabus. However as vertical clearances are also not in the OOW syllabus (they are in the First Mate syllabus) but questions on such are frequently asked, then the cause of tides should not be omitted from study.

Twice-a-day Tides

    Throughout recorded history all the main parts of the solar system have stood in equilibrium with one another. Asteroids and other erratics illustrate gradual change. Whilst the whole universe have tidal affects but only three parts effect any sensible affect. Those three parts of the system are the earth, moon and sun. The earth is held between opposing forces: a centripetal or gravitational force toward the central star, the sun; and an outward centrifugal force. Rather then held statically the two bodies orbit around one another, maintaining this so-called equilibrium. Remember: the earth and sun orbit around their common centre of mass. This barycentre is somewhere inside the sun but not actually at its own centre.

to be continued

Once-a-day Tides