Vocabulary Tide- The periodic rise and fall of the level of water in the ocean Spring tide-The tide with the greatest difference between consecutive low and high tides. Neap tide-The tide with the least difference between consecutive low and high tides.
My Planet Diary pg. 196 A River In Reverse If you were visiting New Brunswick in Canada, you might see the Saint John River flowing into the ocean. But six hours later, you might find that the river changed direction while you were gone! How could this happen? The Saint John River really does reverse course twice a day. At low tide, it empties into the Bay of Fundy, shown below. At high tide, the Bay of Fundy’s tide pushes into the river, forcing the river to run in the opposite direction. The Bay of Fundy’s tides are among the highest in the world. 1.Why does the Saint John River change direction? _______________________ 2. Have you ever seen a Natural event that surprised You? Why was it surprising? _______________________ ________________________
What Causes Tides? Pg. 197 The force of gravity pulls the moon and Earth (including the water on Earth’s surface) toward each other. Tides are caused mainly by differences in how much gravity from the moon and the sun pulls on different parts of Earth. At any one time on Earth, there are two places with high tides and two places with low tides. As Earth rotates, one high tide occurs on the side of Earth that faces the moon. The second high tide occurs on the opposite side of Earth. Halfway between the high tides, water flows toward the high tides, causing low tides.
Tide Cycle Tides are caused mainly by differences in how much gravity from the moon and the sun pulls on different parts of Earth. You can think of Earth as a ball surrounded by a layer of water, as shown in the first picture. The layer is really much thinner than this, but is drawn thicker so It is easy to see. The Near Side: The moon’s gravity pulls a little more strongly on the water on the side closest to the moon than on Earth as a whole. This difference causes a bulge of water on the side of Earth closest to the moon. This bulge causes high tide. The Far Side: The moon’s gravity pulls more weakly on the water on the far side of Earth as a whole. Since Earth is pulled more strongly, the water is “left behind.” Water flows toward the far side, causing high tide. Halfway between the high tides, water flows toward the high tides, causing low tide. Interpret Diagrams : Write an H where high tides occur and an L where low tides occur.
The Sun’s Role pg. 198 The sun is so massive that, even though it is about 150 million kilometers from Earth, its gravity also affects the tides. The sun pulls the water on Earth’s surface toward it. Changes in the positions of Earth, the moon, and the sun affect the heights of the tides during a month.
Spring Tide The sun, the moon, and Earth are nearly in a line during a new moon. The gravity of the sun and moon pull in the same direction. Their combined forces produce a tide with the greatest difference between consecutive low and high tides, called a spring tide.
Neap Tide During the moon’s first-quarter phase, the line between Earth and the sun is at right angles to the line between Earth and the moon. The sun’s pull is at right angles to the moon’s pull. This arrangement produces a neap tide, a tide with the least difference between consecutive low and high tides. Neap tides occur twice a month.
The Sun’s Role Changes in the positions of Earth, the moon, and the sun affect the heights of the tides during a month. What is the position of the moon and where are the tide bulges at third quarter? Infer: Draw the position of the moon and the tide bulges at third quarter. What kind of tide occurs? ___________________
Apply it! High and Low Tides The table shows high and low tides at four times in May 2008, in St. John, New Brunswick. St John is on the Bay of Fundy. 1.Interpret Data- Spring tides occurred At two of the times shown. Which two? How do you know? ________________ ________________________________ 2. Identify- Which measure of central Tendency- mean, median, or mode Represents the average high tide? ________________________________ 3. Calculate- Solve for the average high Tide and low tide. ________________________________ 4. Summarize On which date are the high And low tides closest to the average high And low tides? ____________________
Assess Your Understanding pg. 199 1a. Most coastal areas have _______high tides and _______low tides each day. b. How do the relative positions of the moon and Earth impact tides? ____________________________________________ ___________________________________________________ c. Look at the diagrams on page 198. What is the angle formed by the sun, Earth, and the moon during a neap tide? A spring tide? _____________________________________________ _________________________________________________ I get it! Now I know that tides are caused by ________________ ___________________________________________________