Uploaded by Karen McGahee


-When one of these magnificent sea
creatures finds itself on land, it is a
consequence of the tides.
- Whales move towards the shore
when the tides are high and there is
plenty of water, but fail to leave
when the tides recede, leaving
them stranded on beaches.
- There are a few cases where the
whales have been saved, but many
of these ocean giants perish.
Let’s begin by looking at the
difference between a current and
a tide
pattern of
in the
-Tides are created when the gravitational pull of the moon and
sun interacts with the movement of the earth.
-In other words, the sun and moon both pull on the earth.
-How much influence each has depends on whether the surface
of the earth is closer to the moon or the sun at that moment.
-Currents, on the other hand, are influenced by forces in the
earth’s atmosphere, such as the wind, the temperature of the
water, and the amount of salt in the water.
The Moon and Tides
High Tides
-occur when the ocean is highest on the land, are caused by the pull of the moon.
-When the moon is directly above a point on the beach, it pulls the ocean onto the shore.
-High tides also occur on the opposite side of the planet at the same time.
-The gravitational pull of the moon draws water toward it on one side of the globe.
-At the same time, the other side of the globe is shaped by a force called inertia, which is
the tendency of matter to move in a straight line or stay as it is.
-The combination of gravity and inertia creates a similar bulge, or high tide, on the opposite
-Inertia and gravity are always working to push the ocean’s water.
-When the moon is closest, gravity is __________.
-When gravity is weakest, as it is on the side farthest from the moon, ________dominates. Both
forces will create ___________, so there are ____________a day.
Low Tides
-when the equatorial region is experiencing the high tide, the prime meridian is
experiencing low tide.
-Because the rotation of the moon is slightly different from the rotation of the earth,
these tides are usually about 12 hours and 25 minutes apart.
-This cycle takes a little more than half a day, so there will be a day about every 25
days that has only one tide.
-If the earth were perfectly round and evenly covered in water, the tides would be
exactly twelve hours apart.
-It is the variations in the size of land masses and the depth of the ocean that causes
the tides to take a little longer than 12 hours.
Seasons and Tides
think about how other factors, such as the amount of daylight, change
depending on the earth’s position relative to the sun.
Hurricanes are more common in certain seasons, such as fall on the
East Coast, because of warm water temperatures around the equator.
in the United States, flooding is more likely to happen in the fall
because the moon’s pull is strongest then, meaning that tides will be
-Because tides are regulated by the sun and moon, they are predictable.
-In coastal regions, tides are included in weather reports.
-While gravitational forces have the biggest influence on tides, there are
actually about 140 different elements that shape their movement.
-Predictions of high tides are generally accurate to within 1.2 inches, but an
unusual weather event can change that.
-you have probably experienced a day or two that were unexpectedly
warm in the winter or unexpectedly cool in the summer.
-when tides break their usual patterns because of unusual weather, they are
called meteorological tides.
Review Questions
1. The example of a whale beached by the tides illustrates that
tides occur twice a day.
tides impact marine life.
tides are a leading killer of whales.
tides are usually deadly and destructive.
2. Tides are most visible
on shores and coasts.
in the middle of the ocean.
wherever the water temperature is warmest.
in freshwater bodies, such as lakes, rivers, and streams.
3. All of the following influence tides except
the sun
the moon
the air temperature
the rotation of the earth
4. A high tide will occur
usually only once in a 24-hour period.
only in bodies of water close to the moon.
on both sides of the earth at the same time.
when proximity to the sun makes the days longer.
5. Which of the following explains why tides occur every 12 hours and 25
Variations in the land and depth of water make the tides uneven.
It takes 24 hours and 50 minutes for the earth to make a complete rotation.
Early scientists misunderstood how to calculate tides, and their error persists to
this day.
In some seasons, the rotation of the earth is slower than others, requiring
additional time.
6. In the United States, the moon’s pull is strongest during which season?
7. When swimming at the beach, you are most likely to encounter
tidal currents.
meteorological tides.
thermohaline currents.
8. All of the following can influence tides except
heavy rains.
the shoreline.