Your assignment is to listen to the recording and read this webpage as you listen. You are also supposed to copy the notes at the end of each recording. When you finish copying the notes, go back over the reading material and study the pictures and charts so that you understand what you have read. You may also want to listen to the recording again.
Although the wind plays a major role in most ocean motion, it is not the predominant cause of tides, the slow, periodic rise and fall of ocean waters.
The water level of the ocean rises and falls throughout the day. Early in the day, ocean water rises and covers part of the beach. Later in the day, the ocean level falls. The beach is exposed. These regular changes in ocean water levels are called tides. A low water level is called low tide. A high water level is called high tide.
A tide is a rise or fall of the ocean’s surface caused mostly by the gravitational pull of the moon. The gravitational pull of the sun also affects a tide, but not as much as that of the moon.
Tides are caused by two factors: the gravitational pull of the Moon and Sun and the inertia of water in the oceans on Earth. The combination of gravity and inertia are responsible for the creation of two major tidal bulges on the Earth. Gravity creates a bulge of water on the side of the Earth facing the Moon and inertia creates a bulge on the side of the Earth facing away from the Moon. The sun also affects the size and position of the two tidal bulges.
The Sun, Moon, and Earth are three extremely large objects separated by very great distances. Despite the large distances between them, each object affects the others. Earth is kept in orbit around the sun by the gravitational forces between them. The Moon is kept in orbit around the Earth by the gravitational forces between them. These forces are mutual, meaning each object attracts and is attracted to the other. However, the gravitational pull of the Sun is almost 200 times greater than the Moon, but since the Moon is almost 400 times closer to the Earth than the Sun, the Moon’s gravitational pull is more than twice that of the Sun.
Click on the link below to see the tides in motion;
Most coastal areas, with some exceptions along the coast of
Four times a month, the Sun’s effect on tides is noticeable. Twice a month, the Sun, Moon, and Earth align to produce very high and very low tides called Spring Tides. The name has nothing to do with the season. Spring is from a Saxon word meaning “to swell”. Spring Tides occur during the New Moon and Full Moon. When the Sun and Moon are at right angles to each other, the gravity of each pulls the ocean water in different directions. In this position, there is little difference between the depth at high and low tide. These tides are called Neap Tides. Neap is from a Saxon word meaning “scarce or lacking”. Neap Tides occur twice a month, during the first and third quarter phases of the Moon. Spring and Neap Tides occur twice every 29.5 days (or twice each month).
1. tides-the regular change in the level of Earth’s oceans.
2. flood tide-the incoming, or rising tide
3. ebb tide-outgoing, or falling tide
4. Moon’s gravity causes most tides.
5. changing tides happen about every 6 hours and 12 minutes.
6. there are about 4 tides every 24 hours and 50 minutes, two high tides and two low tides.
7. Spring tide is an extra high and extra low tide caused by the alignment of the Moon and the Sun.
8. Full Moon and New Moon cause the Spring tides.
9. Neap tide is smaller tidal change than normal caused by the Moon and Sun being at a 90 degree angle, a right angle.
10. 1st quarter Moon and 3rd quarter Moon cause Neap tides.
11. intertidal zone-the land that is exposed (the beach) during low tide but is covered during high tide.
We have talked about tides and waves, but what is a “tidal wave”? Tidal waves are actually seismic sea waves or tsunamis. Students may want to read more about this phenomenon.
Some of the largest
and most destructive ocean waves are not formed by wind. They are caused by
movements of the Earth’s crust, such as earthquakes on the ocean floor.
STOP! Copy your notes.
Your team members should be able to answer the following questions.
1. What are tides?
2. What causes tides?
3. How many tides occur each day?
4. Name four tides that occur, tell when they occur, and
how they occur.
5. Which of these tides causes the greatest intertidal zone?
6. How often do spring tides occur?
Neap tide: The smallest rise and fall in tides that occur when the sun and the moon are at right angles to the Earth.
Spring tide: The greatest rise and fall in tides that occur when the sun and the moon are in line with the Earth.
Tsunami: The Japanese word for seismic sea wave. A series of traveling ocean waves of extremely long length generated by disturbances associated primarily with earthquakes occurring below or near the ocean floor. Underwater volcanic eruptions and landslides can also generate tsunamis.