How the Tides Work
The Earth >
Have you ever been to the beach and noticed a newly arrived group of friends set up their towels a little too close to the water line? As the hours go byand the friends bask in the sun, the ocean waters seem to sneak up on them, almost imperceptibly. At just the right time when just the right wave comes in, they are suddenly deluged in a mini-flood of seawater that soaks towels, CD players, and sunburned bodies.
They have experienced the dreaded rise of the ocean’s tide. Here’s how it works.
Most of us talk as if the tide is “coming in” or “going out,” and from our point of view that’s correct. But on the global scale, we on the Earth’s crust are actually spinning into, then out of, high waters.
Enter the Moon.
The Moon, being a massive heavenly body with gravity, pulls on us just as we pull on it. And the part of Earth closest to the Moon is pulled with greater force precisely because it is closer. In fact, the crust of our planet that is closest to the Moon actually bulges out towards it by a few centimeters. But the ocean’s waters are much more easily shaped than the rigid crust and they bulge upward on average more than a meter.
Meanwhile, Earth just keeps spinning on its axis. It is when we spin into this great pile up of water that the ocean seems to rise and the tide “comes in.” As we pass through and by this watery bulge, the tide “goes out.”
Now
on the opposite side of the Earth, a similar high tide scenario is being
played out. But here the Moon is pulling harder on the planet and less
on the far side oceans, so those waters are being “left behind.”
Picture it like this: Imagine tying a water-soaked sponge to a string and swinging it around your head. The water starts flinging off the sponge and onto curious, and now annoyed, onlookers.
The ocean waters on the opposite side of the Earth are sort of being flung like this – but thankfully only about a meter or so. Nevertheless, the net effect is a rising of the waters on the other side of the Earth than the Moon resulting in a second high tide for the day.
Now even though the Moon plays the big major role in our Tidal Play, the Sun has a supporting role. It is plenty massive and has plenty of gravity but it is plenty far away, too. So it pulls on the water with only half the force.
But imagine what happens when the Moon and Sun work together; one plenty big tide, that’s what. When the Sun and Moon are on the same side of our planet (New Moon) or on the opposite side (Full Moon), together they can raise that water under them to the highest heights of the month. This is called a spring tide, from the German “springen” – to spring up.
When the Sun and Moon are at odds with each other - at first and last quarter phases - they pull the waters in different directions and nearly cancel each other out. This wimpy high tide is called the neap tide.
Tides are a great thing; they help churn the waters, they erode the coastline, they allow the survival of multitudes of tidal species, and their friction has helped slow this planet to a comfortable 24–hour day.
When you go to the beach this season, beware the tide, but be thankful, too.
Posted by Administrator at 2001.05.13 08:32 AM | Comments (0)
