Introduc)on To Tides Bay of Fundy Nova Sco/a, Canada The Worlds Lowest and Highest Tides Tides I. Defini)on: the periodic rise and fall of sea level A. measured rela)ve to points on land B. highest level = high )de C. lowest level = low )de II. Occurrence: there are 2 high )des and 2 low )des each day. Tides (cont.) III. Tidal Range: the difference in feet, or meters, between a high /de and the next low /de •  /dal ranges vary due to topography and la/tude •  EX: low range: Gulf of Mexico /dal range is 1m •  high range: Bay of Fundy in Canada is as high as 15m IV. Cause of /des A. Tides are caused by gravita/onal forces from the moon and the sun B.  Gravity is a func/on of mass and distance C.  The moon, which is much closer to the earth than the sun, exerts a stronger gravita/onal force on the oceans Ques/on: How does one moon cause two /des? Here’s how… IV. Causes of /des, cont. D.  The force of gravity decreases with distance, so the moon exerts a stronger gravita/onal pull on the near side of earth, and a weaker gravita/onal pull on the far side. E.  The oceans near the moon are pulled up towards the moon crea/ng one /dal bulge. F.  On the far side of the planet, the earth is pulled towards the moon resul/ng in the water on the far side being effec/vely leW behind in a /dal bulge. IV. Tidal Cycle
a. The moon revolves around the earth at a rate
of 12!/day (1 revolution/month)
b. The revolution is in the same direction as the
earth’s rotation
c. By the time the earth has completed one
rotation, the moon has shifted 12 !. So, it takes
an extra 50 minutes for the moon to be in the
same position relative to a point on earth.
d. A tidal cycle is 24 hours and 50 minutes
Link to anima/on High and Low /des are 50 minutes later every day! V. The Sun’s Effect on Tides •  Because of its size, the sun exerts a gravita/onal force 180 /mes stronger than the moon! •  But, gravita/onal a\rac/on decreases as the distance between bodies increases •  The sun’s influence on /des is much smaller than the influence of the moon •  The sun’s pull can either heighten the moon’s effect or counteract it depending on where the moon is in rela/onship to the sun. V. The Sun’s Effect on Tides •  When the sun, moon and earth are aligned, the sun’s gravita/onal effect heightens that of the moon. •  High /des are higher and low /des are lower (large /dal ranges) •  These /des are called spring /des •  Spring /des occur at the new moon and full moon. V. The Sun’s Effect on Tides •  When the sun’s gravita/onal effect is perpendicular to that of the moon, the sun’s gravity counteracts the effects of the moon •  The result is lower high /des and higher low /des (small /dal ranges) •  This occurs when the moon is in its first quarter and it’s third quarter •  These are called neap /des Link to anima/on New Moon 10/8 1st Quarter 10/14 Full Moon 10/23 3rd Quarter 10/30 The
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