1. Moon & Tides By Diana L. Duckworth Rustburg High School Campbell County, VA

2. Cause of Tides Gravitational attraction of Sun & Moon for Earth & its water Sun is larger but is farther away than Moon F= Gm 1 m 2 /r 2 indicates that distance has a greater impact on gravity Moon affects tides to greater extent than Sun

3. Equilibrium tides on water covered Earth Mass of Moon pulls water toward moon & pulls Earth away from water on opposite side Creates two tidal bulges –Direct high tide under moon –Indirect high tide away from moon Low tides are in between Direct high tide Indirect high tide Low tide Earth rotates through 2 high and 2 low tides a day! Moon NP

4. Timing of Tides Moon is at highest point 50 minutes later each day High tides come when moon is overhead & 12 hours & 25 minutes later Tides come 50 minutes later each day –24 hrs &50 minutes between successive direct tides –12 hrs & 25 minutes between high tide & next high tide –6 hrs &12.5 minutes from high tide to low tide

5. Tidal Cycle

6. Another cycle

7. Kinds of tides On a water covered earth two high & two low tides would occur each day - semidiurnal tides as on U.S. East Coast Continents get in way, so two other kinds of tides –Diurnal - one high & one low tide each day Gulf of Mexico –Mixed - mostly semidiurnal but diurnal occasionally as on U.S. West Coast

8. Tides Correlated with Moon Phases Spring tides - 2 weeks apart Largest tidal range of month Occur when Sun & Moon both pull on the high tides –Largest range during New Moon –Next largest range during Full Moon Full Moon New Moon Sun Earth

9. Tides Correlate with Moon Phases Neap Tides Two weeks apart Low tidal ranges Sun pulls on low tides Moon pulls on high tides Occur during 1st & Last Quarter Moons Sun First Quarter Last Quarter Low High Low

10. Other factors affecting tides Because distance is factor in gravity, height of tides affected by apogee & perigee of moon also by aphelion & perihelion of Earth Greatest tidal range would occur when Earth is in perihelion & Moon is at perigee during New Moon Phase!