Waves
Q: What
causes waves?
A:
The wind. When the wind blows over the ocean's surface it
creates waves. The size of the wave depends
upon how far, how fast and how long the wind
blows. A gentle breeze will form ripples on the
surface but
strong, steady winds over long distances create large waves.
Even on a day when there is no wind at all, there
may still be large waves crashing on the beach. These
waves were probably created by a distant storm out at
sea and the wave energy traveled for days before it arrived.
Q: Why
doesn't a wave push a boat across the ocean?
A:
Because waves travel through water but do not take the water
with them. Let me try to explain: As a
wave arrives, it lifts water particles.
These particles travel forward, then down and back so that each
particle
completes a rolling circle and
ends up back where it began. This is
why a boat will "bob" in the waves but
not travel with the wave. The boat
moves forward at the height of the
wave but then as the wave falls, the
boat will move back to approximately
the same place it was before the wave arrived. This
circling movement of water particles near the surface sets
off smaller circling movements below them and the wave energy
also begins the next group of water particles to
begin the circular movement thus continuing the wave until it
reaches the shore.
Q. Don't
waves cause the tides, or the tides cause the waves?
A.
The tides are a result of the
effects of gravity between the Earth, the Sun and the Moon and
have nothing
to do with waves.
All
the surfaces of the Earth are pulled toward the sun and the
moon. This force has little effect on the land
but it does have a very great and obvious effect on the waters
of the Earth's oceans. Twice each month, the
tidal range reaches a maximum and these large tides are called
"Spring Tides." Halfway through the monthly
cycle, the range is much smaller. These very weak tides are
called "Neap Tides."
As the moon
rotates around the Earth, it pulls the water on the nearest side
of the Earth outward into a bulge. A similar bulge, on the
opposite side of the
Earth is also caused by the water being thrown outward by the
planet's spin.
These two bulges travel around the globe, producing two high
tides each day.
Twice each month, during the times of the new moon and a full
moon, the sun
and moon are in a straight line and their gravitational pull
combine and produce
what is called Spring Tides. During Spring Tides, the high
tides are very high and
the low tides are very low.
When
the sun and moon are at right angles from the Earth, during the
quarter
phases of the moon, the gravitational pull on the oceans is much
less, producing
a smaller difference between high and low tide. This is known
as a Neap Tide.
