Chapter 21 Section 3 Chapter 21 Section 3 Review Page 534Review Page 534

1. Describe how the 1. Describe how the moon causes tides.moon causes tides.

• As the moon revolves around As the moon revolves around Earth it’s gravity pulls on Earth’s Earth it’s gravity pulls on Earth’s waters. This creates two high waters. This creates two high tide bulges on opposite sides of tide bulges on opposite sides of Earth and two low tides in Earth and two low tides in between.between.

Moon Creates TidesMoon Creates Tides

2. Explain how the sun 2. Explain how the sun can influence the moon’s can influence the moon’s effect on tides.effect on tides.

• The sun can pull in the same The sun can pull in the same direction as the moon’s gravity direction as the moon’s gravity and increase the size of tides. It and increase the size of tides. It can pull at right angles to can pull at right angles to decrease the size of tides.decrease the size of tides.

3. Compare spring tides 3. Compare spring tides and neap tides.and neap tides.

• Spring tides happen when the Spring tides happen when the sun and moon pull together to sun and moon pull together to increase tide size. Neap tides increase tide size. Neap tides happen when sun and moon pull happen when sun and moon pull at right angle to each other and at right angle to each other and lower the tide size.lower the tide size.

Moon and Sun Create TidesMoon and Sun Create Tides

Spring Tides and Neap TidesSpring Tides and Neap Tides

4. Describe how ocean 4. Describe how ocean basins affect tidal basins affect tidal patterns.patterns.

• Differences in the size, shape, Differences in the size, shape, depth, and location of the depth, and location of the landmasses around an ocean landmasses around an ocean affect the number and size of the affect the number and size of the tides.tides.

Arrival Times of TidesArrival Times of Tides

5. Compare the movement 5. Compare the movement of ocean water in the of ocean water in the open ocean with the open ocean with the movement of ocean movement of ocean water in narrow bays.water in narrow bays.

• Tidal currents in open oceans are Tidal currents in open oceans are much smaller than those at the much smaller than those at the coasts. In narrow bays, tidal coasts. In narrow bays, tidal oscillations increase the effects oscillations increase the effects of tidal bulges, producing larger of tidal bulges, producing larger tidal ranges.tidal ranges.

Ocean Tide in a Narrow BayOcean Tide in a Narrow Bay

6. Describe how a tidal 6. Describe how a tidal bore forms.bore forms.

• Where a river enters an ocean Where a river enters an ocean through a long, narrow bay a through a long, narrow bay a surge of tidal water may flow surge of tidal water may flow upstream in a wave called a tidal upstream in a wave called a tidal bore.bore.

Tidal BoreTidal Bore

The EndThe End