Tides

Gravity Earth’s gravity holds water to the surface. With no moon, sea level would be the same everywhere. The Moon’s gravity pulls Earth and its oceans. Moon Earth Moon’s gravity

Tidal Gravity The Moon’s gravity is strongest at the closest point. –Near face ocean pulled most –Far face ocean pulled least –Sides pulled slightly in Moon Earth Moon’s gravity

Ocean Tides From Earth a person doesn’t sense the Moon’s pull. –Near and far faces of the ocean bulge away –Sides are pulled slightly in Tides occur twice a day as Earth rotates. Moon Earth Moon’s tidal pull

Spring and Neap Tides The Sun also creates a tide, but it is weaker than the Moon. –Spring tide with Moon in line with the Sun –Neap tide with Moon at right angle to the Sun moon earth sun moon earth sun spring tide neap tide

Tidal Friction Tides from the Moon cause the ocean to drag against the crust. –Liquid outer core also drags This will slow Earth’s rotation over time.

The Changing Day The day becomes seconds longer each century. 500,000,000 years ago there were –22 hours in a day –400 days in a year The moon recedes from the earth by 4 cm each year. –Angular momentum When the Moon formed it was –22,500 km from Earth, –now 375,000 km

The Changing Month Billions of years in the future there will be 1 “day” = 47 present days 1 “month” = 1 “day” The Earth-Moon system will be locked facing each other. The Moon will be farther and appear much smaller. Moon side Earth far side Moon