The gravitational force of the moon is one ten-millionth that of earth, but when you combine
other forces such as the earth's centrifugal force created by its spin, you get tides.
The sun's gravitational force on the earth is only 46 percent that of the moon. Making the moon the
single most important factor for the creation of tides.
The sun's gravity also produces tides. But since the forces are smaller, as compared to the
moon, the effects are greatly decreased.
Tides are not caused by the direct pull of the moon's gravity. The moon is pulling upwards on the water
while the earth is pulling downward. Slight advantage to the moon and thus we have tides.
Whenever the Moon, Earth and Sun are aligned, the gravitational pull of the sun adds to that of the moon
causing maximum tides.
Spring tides happen when the sun and moon are on the same side of the earth (New Moon) or when the
sun and moon are on opposite sides of the earth (Full Moon).
When the Moon is at first quarter or last quarter phase (meaning that it is located at right angles
to the Earth-Sun line), the Sun and Moon interfere with each other in producing tidal bulges and
tides are generally weaker; these are called neap tides.
Spring tides and neap tide levels are about 20% higher or lower than average.
Offshore, in the deep ocean, the difference in tides is usually less than 1.6 feet
The surf grows when it approaches a beach, and the tide increases. In bays and estuaries,
this effect is amplified. (In the Bay of Fundy, tides have a range of 44.6 ft.)
The highest tides in the world are at the Bay of Fundy in Nova Scotia, Canada.
Because the earth rotates on its axis the moon completes one orbit in our sky every 25 hours (Not to be confused with
moon's 27 day orbit around the earth), we get two tidal peaks as well as
two tidal troughs. These events are separated by about 12 hours.
Since the moon moves around the Earth, it is not always in the same place at the same time each day.
So, each day, the times for high and low tides change by 50 minutes.
The type of gravitational force that causes tides is know as "Tractive" force.