What Causes The Tides To Occur?

January 6, 2012 DO NOW: Update T.O.C. Take out H.W. Take out yesterday’s tidal lab. Turn to a partner and discuss what patterns you noticed after graphing daily tides data. Be prepared to discuss your observations as a class

Tides Lab Follow instructions on your lab sheet. Use the table and graph provided to complete the lab activity. Class discussion of results.

Tides Tides occur due to the gravitational pull of the Moon & Sun on the Earth’s oceans. Predict: Which has more effect on Earth’s tides: Sun or Moon? There are 2 high and low tides that occur every day. The sun's gravitational force on the earth is only 46 percent that of the moon. Making the moon the single most important factor for the creation of tides. The sun's gravity also produces tides. But since the forces are smaller, as compared to the moon, the effects are greatly decreased.

Spring Tides & Neap Tides Occur when the moon is in the full or new phases. (Straight line) When high tides are at their highest and low tides are at their lowest (largest range between high & low tide) these are known as spring tides. Neap tides Occur when the moon is in the first or last quarter phases. (Right angles) When the range between high and low tide is at it’s smallest, these are known as neap tides. Spring Tides When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon. Neap Tides During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons. Whenever the Moon, Earth and Sun are aligned, the gravitational pull of the sun adds to that of the moon causing maximum tides. When the Moon is at first quarter or last quarter phase (meaning that it is located at right angles to the Earth-Sun line), the Sun and Moon interfere with each other in producing tidal bulges and tides are generally weaker; these are called neap tides. Spring tides and neap tide levels are about 20% higher or lower than average.

Spring & Neap Tide Animation

How do ocean tides affect humans? Fishing Fish change movement & migration patterns based on the flow of tides. Vessel Movements Movement of ships Construction of docs Availability of certain docs based on tide Flooding & Erosion Power Generation Hydroelectric dams Power buoys Charting and following fish movement patterns is crucial for the fishing industry & provides us a major source of protein. Flooding of low-lying areas especially those below sea-level is a huge problem. Erosion of coastlines happens at different intervals based on location and how the landmass is built up from the ocean floor.

In closing… Describe spring & neap tides. Describe the phase & position of the moon during spring & neap tides.