Spencer Bryant, age 10 of Mercer Island, Washington for his question:
What makes the tides go in and out?
Andy says that more people seem to notice the tides during the summer months. But that is only because more people visit the beaches during the summer months: Actually the tides wash up and down the shares twice every twenty. four hours, every week and month, year in and year out. Far the great laws which control the rising and telling tides never stop working.
The earth, the sun and moon are kept in their proper places by the mighty force of gravitation. This great pulling power is present in every object. Every object upon earth pulls, or attracts other objects with its force of gravity: The bigger and nearer the object, the greater its power to pull or attract other objects. And everything upon earth is held there by the far, far greater pulling power of our massive globe.
This same poorer in our earth pulls at the moon. And the moon, being smaller, pulls back with less force. The huge sun pulls at both earth and moon. The little moon has twice as much power to pull at the earth than has the giant sun because it is so much closer. And it uses its gravitation to pull hard enough to wrench parts of the earth out of shape,
As the earth runs, first one side then another is facing the moon. And the moon does its pulling on the part of earth facing it. It pulls up the oceans into vast heaps of water. As the earth runs around, the great heap of beater lags along the side facing the moon. On the opposite side of the earth, the water feels less of the moon’s pull: It falls behind and piles up into a heap of water of its own. These two piles of water on the opposite sides of the globe take away the water from the areas between.
Where the moon has pulled up the watery high tides creep up the beaches. At the same time, high tides are creeping up the beaches on the opposite side of the globe. In between, the water is falling to form low tides. As the earth turns, high tide and low tide follow each other around the beaches.
When the moon is new and when the moon is full then the earth, sun and moon are in a straight line. The pulling power of the sun is added in the same direction as that of the moon. The tides on earth are pulled highest and lowest in what we call the spring tides. In the first and third quarters of the month, the moon and sun are pulling at the earth in opposite directions. In what we call the neap tides the high tides are less high and the law tides less low,
Twice each day, the water on your favorite beach is pulled up in a high tide once soon after it has passed directly under the moon and once when it is directly opposite to the moon. Twice each day the high tide falls away as the water flows to make high tides on other beaches,