The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. What causes the tides? Why does tidal range vary? (D)

Tides are caused by the gravitational pull of the moon and the sun on Earth's oceans. The gravitational force of the moon is stronger than that of the sun because it is much closer to Earth. This force creates a bulge in the water on the side of Earth facing the moon and another bulge on the opposite side (due to the centrifugal force). As Earth rotates, the ocean water moves into and out of these bulges, causing the water level to rise and fall, which are known as tides.

Tidal range is the difference in height between consecutive high tides and low tides. Tidal range varies due to the relative positions of Earth, the moon, and the sun, as well as the specific geographic location of a coastline. When the sun, the moon, and Earth are aligned (during full moon or new moon), their combined gravitational pull creates higher high tides and lower low tides, resulting in a larger tidal range, known as spring tides. When the sun, the moon, and Earth form a right angle (during the first and third quarter moon), their gravitational pull partially cancels each other out, causing lower high tides and higher low tides, resulting in a smaller tidal range, known as neap tides.

In addition to the relative positions of Earth, the moon, and the sun, tidal range can be affected by the shape of the coastline, seafloor topography, and other local conditions. For example, narrow bays and estuaries can cause water to funnel into a smaller area, amplifying the tidal range, while large, open coastlines may experience smaller tidal ranges. Seafloor topography can influence the flow of ocean currents and tidal waves, which can also affect the tidal range. Local conditions such as wind and atmospheric pressure can have a short-term impact on tides. In summary, tides are caused by the gravitational pull of the moon and the sun on Earth's oceans, with the moon having a stronger influence due to its closer proximity. Tidal range, or the difference in height between high tides and low tides, varies based on the relative positions of Earth, the moon, and the sun, as well as local factors such as coastline shape, seafloor topography, and other conditions.