of the Tides p.2
Think About This!
Stop the world, stop the moon too, and there will still be tides.
To understand the basic
reason for the tides, stop the moon in its orbit and let it begin
to fall to earth. While were stopping things, stop the earth
from spinning, too. The earths gravitational pull accelerates
the moon toward the earth. At the same time, the gravitational pull
of the moon accelerates the earth toward the moon. Take a snapshot
of these falling bodies and examine whats happening on the
are created by the moon's gravity pulling the earth. Water flows
more easily than solid ground and so responds
more to the pull of tidal forces. High tide would be occuring
on the sides of this globe that are in the "lunar bulge."
Its about 13,000
kilometers from one side of the earth to the othera considerable
distance. Because the gravitational pull of the moon decreases with
distance, a chunk of earth closest to the moon feels a stronger
gravitational attraction by the moon than a chunk at the center
of the earth, and both feel a larger force than a chunk on the far
side of the earth. If it were free of the earth, the chunk nearest
the moon would accelerate faster and be pulled away from the center
of the earth by the greater attractive force, while the chunk on
the far side of the earth would be left behind by the rest of the
Because of the
earths gravity, which pulls things toward the center of the
earth, the various chunks arent free to fall separately toward
the moon. Instead, the gravitational attraction of the moon creates
tidal bulges. There are bulges in the solid rock of the earth, although
they are small and difficult to notice. But most of the earths
surface is covered by water, which can move about more easily than
rock. The water on the side of the earth nearest the moon is pulled
up by the moons gravity about half a meter, creating a tidal
bulge or a high tide, with the surrounding water pulled toward the
bulge. The water on the opposite side of the earth is "left
behind," creating a second high tide.
do the tides get later each day?
See how the sun creates tides, too!