Chapter 9

# Chapter 9 - Intro to Oceanography Chapter 9 Tides periodic...

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Intro to Oceanography : Chapter 9 Tides – periodic raising and lowering of average sea level that occurs throughout the oceans of the world Tides are fundamentally very long and regular shallow-water waves Gravitational attraction of the Sun and Moon generates ocean tides I. What Causes the Tides? a. Tides are generated by forces imposed on Earth that are generated by a combination of gravity and motion among Earth, the Moon, and the Sun. b. Tide-Generating Forces i. The Moon and the Earth rotate around a common center of mass called the barycenter, which is located 1600 km beneath Earth’s surface ii. They are held together by gravity and motion, which prevents the Moon and the Earth from colliding iii. Gravity also tugs every particle of water on Earth toward the Moon and the Sun, thus creating tides on Earth iv. Gravitational and Centripetal Forces in the Earth-Moon System 1. Gravitational force is derived from Newton’s law of universal gravitation, which state that every particle of mass in the universe attracts every other particle of mass 2. If mass increases, then gravitational force increases 3. If distance increases, then gravitational force greatly decreases 4. Greatest at zenith (Z) – point closest to the Moon 5. Weakest at nadir (N) – point farthest from the Moon 6. Centripetal force “tethers” an orbiting body to its parent, pulling the object inward toward the parent, “seeking the center” of its orbit 7. The Earth and the Moon are tethered by gravity (centripetal force) v. Resultant Forces 1. Resultant forces – the mathematical difference between the supplied gravitational (G) forces and the required centripetal (C) forces 2. Centripetal is a force that is required the keep the particles in a perfectly circular path 3. Gravity is the force actually provided for this purpose vi. Tide-Generating Forces 1. The zenith and nadir have vertical resultant force having no tide-generating effects 2.

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