ความคิดเห็นที่ 11
 
อืมใช่ๆ มันเป็นเรื่อง tidal force จริงด้วยแฮะ
ลองดูที่นี่นะครับ
http://en.wikipedia.org/wiki/Tide
ผมไม่แปลดีกว่าเกรงว่าจะเพี้ยน :-D
Tidal forces can also be analyzed in the following way: each point of the Earth experiences the Moon's radially decreasing gravity differently; they are subject to the tidal forces of Figure 6, which dominate. Finally, most importantly, only the horizontal components of the tidal forces actually contribute tidal acceleration to the water particles since there is small resistance. The actual tidal force on a particle is only about a ten millionth of the force caused by the Earth's gravity.
The ocean's surface is closely approximated by an equipotential surface, (ignoring ocean currents) which is commonly referred to as the geoid. Since the gravitational force is equal to the gradient of the potential, there are no tangential forces on such a surface, and the ocean surface is thus in gravitational equilibrium. Now consider the effect of external, massive bodies such as the Moon and Sun. These bodies have strong gravitational fields that diminish with distance in space and which act to alter the shape of an equipotential surface on the Earth. Gravitational forces follow an inverse-square law (force is inversely proportional to the square of the distance), but tidal forces are inversely proportional to the cube of the distance. The ocean surface moves to adjust to changing tidal equipotential, tending to rise when the tidal potential is high, the part of the Earth nearest the Moon, and the farthest part. When the tidal equipotential changes, the ocean surface is no longer aligned with it, so that the apparent direction of the vertical shifts. The surface then experiences a down slope, in the direction that the equipotential has risen.
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eera  
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4 มิ.ย. 52 22:52:17
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