GED Science Practice Test: Tides

Another interaction between the moon, earth, and sun are the tides.  Tides are the cyclical raising and lowering of water levels, due to the gravitational pull of the sun and the moon on earth’s water.  First, let’s consider how the moon affects tides on earth.  The liquid water on earth is gravitationally attracted to the moon.  Where the earth and moon face each other, water experiences high tide.  Interestingly, due to the inertia of the water, high tide is also experienced on the opposite side of earth.  Observe these relationships in the diagram below:

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However, the moon is not the only space object that pulls on the water on earth.  The sun has a similar effect on the earth’s water and the tides.  When the sun, moon, and earth are lined up, the water experiences a very high tide, called a spring tide.  A spring tide is pictured in the diagram below:

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Sometimes, the sun, moon, and earth are not aligned.  This results in the sun pulling on the earth’s water in one direction, and the moon pulling on earth’s water in a different direction.  When the sun and moon are pulling on earth’s water at 90 degree angles to each other, this is called a neap tide.  The following diagram shows the positions of the sun, moon, and earth necessary to create spring and neap tides:

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