Tides • Definition: the periodic rise and fall of sea level within a day a. tides are measured relative to points on land b. highest level = high tide c. lowest level = low tide • Tidal Ranges: the difference in feet, or meters, between a high tide and the next low tide • tidal ranges vary due to topography and latitude Examples: • Low Range: Gulf of Mexico tidal range is 1m • High Range: Bay of Fundy (between New Brunswick and Nova Scotia) is as high as 15m
III. Causes of Tides a. Gravitational forces causes the Earth and moon to be pulled towards one another b. The liquid on the side of the Earth closest to the moon is pulled toward the moon, producing a bulge. c. The center of the Earth is also pulled toward the moon. Thus, the water on the opposite side of the earth is ‘left behind’ causing a bulge on the opposite side of the Earth. L d. Because there are two bulges, a point on Earth experiences two high tides and two low tides in one day! H H Bulge L
IV. Tidal Cycle a. The moon rotates around the earth at a rate of 12/day (1 revolution/month) b. The rotation is in the same direction as the earth’s spin 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 is24 hours and 50 minutes! High and Low tides are 50 minutes later every day!
V. The Sun’s Effect on Tides a. Because of it’s size, the sun exerts a gravitational force 180 times stronger than the moon! b. BUT, gravitational attraction decreases as the distance between bodies increases c. The sun’s influence on tides is much smaller than the influence of the moon d. The sun’s pull can either heighten the moon’s effects or counteract them depending on where the moon is in relation to the sun
e. Spring Tides • When the sun, moon and earth are aligned, the sun’s gravitational pull heightens the effects of the moon. • High tides are HIGHER and low tides are LOWER (large tidal ranges) • These tides are calledSPRING TIDES. • Spring tides occur at the full moon and newmoon.
f. Neap Tides • When the sun’s gravitational pull is perpendicular to that of the moon,the sun’s pull counteracts the effects of the moon • The sun pulls water away from the areas of high tide • The result is LOWER high tides and HIGHER low tides (small tidal ranges) • This occurs when the moon is in its first quarter or it’s third quarter