These bulges represent high tides. If the moon's gravity is pulling the oceans toward it, how can the ocean also bulge on the side of Earth away from the moon? It does seem a little weird. It's all because the tidal force is a differential force—meaning that it comes from differences in gravity over Earth's surface. Here's how it works:.
On the side of Earth that is directly facing the moon, the moon's gravitational pull is the strongest. The water on that side is pulled strongly in the direction of the moon. On the side of Earth farthest from the moon, the moon's gravitational pull is at its weakest. At the center of Earth is approximately the average of the moon's gravitational pull on the whole planet.
Arrows represent the force of the moon's gravitational pull on Earth. To get the tidal force—the force that causes the tides—we subtract this average gravitational pull on Earth from the gravitational pull at each location on Earth. The result of the tidal force is a stretching and squashing of Earth.
This is what causes the two tidal bulges. Arrows represent the tidal force. It's what's left over after removing the moon's average gravitational pull on the whole planet from the moon's specific gravitational pull at each location on Earth.
An even smaller amount can be used as drinking water. Along coasts, the water slowly rises up over the shore and then slowly falls back again. The gravitational pull of the moon and the rotational force of the Earth cause tides to rise and fall across the planet. The species living in coastal areas most affected by changing tides have unique ways of surviving.
Encyclopedic entry. Every now and then, a planet or moves into the shadow of another one. We call this an eclipse.
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Interactives Any interactives on this page can only be played while you are visiting our website. Now it is low tide in that area. As the Earth keeps rotating, another high tide occurs in the same area when it is on the side of the Earth opposite the moon low high tide. The Earth continues spinning, the tide ebbs, another low tide occurs, and the cycle 24 hours long begins again.
The vertical difference between high and low tide is called the tidal range. Although the sun is almost times farther away from the Earth than is the moon, its high mass still affects the tides. The shape of a seacoast and the shape of the ocean floor both make a difference in the range and frequency of the tides.
Along a smooth, wide beach, the water can spread over a large area. The tidal range may be a few centimeters. In a confined area, such as a narrow, rocky inlet or bay , the tidal range could be many meters. The lowest tides are found in enclosed sea s like the Mediterranean or the Baltic. They rise about 30 centimeters about a foot. The largest tidal range is found in the Bay of Fundy, Canada. There, the tides rise and fall almost 17 meters 56 feet.
Twice each month, the moon lines up with the Earth and sun. These are called the new moon and the full moon. This is the new moon. When the Earth is between the sun and moon, the moon reflects sunlight. This is the full moon. The combined pull can cause the highest and lowest tides, called spring tide s. Spring tides happen whenever there is a new moon or a full moon and have nothing to do with the season of spring.
When this happens, the pull of the sun and the moon are weak. This causes tides that are lower than usual. These tides are known as neap tide s.
Tidal Features Tides produce some interesting features in the ocean. Tides are also associated with features that have nothing to do with them. A tidal bore occurs along a coast where a river empties into the ocean or sea.
The tidal bore is a strong tide that pushes up the river, against the river's current. This is a true tidal wave. The huge tidal bore of the Amazon River is called the pororoca. The pororoca is a wave up to 4 meters 13 feet tall, traveling at speeds of 15 kilometers 9 miles per hour. The pororoca travels 10 kilometers 6 miles up the Amazon.
While a tidal bore is a tidal wave, a tsunami is not. Tsunamis are associated with tides because their reach surpass es the tidal range of an area. A red tide is another term for an algal bloom. Algae are microscopic sea creatures. Finally, rip tide s are not a tidal feature. Rip tides are strong ocean current s running along the surface of the water.
A rip tide runs from the shore back to the open ocean. Rip tides can be helpful to surfers, who use them to avoid having to paddle out to sea.
Rip tides can also be very dangerous to swimmers, who can be swept out to sea. Intertidal Life The land in the tidal range is called the intertidal zone. The intertidal zone is often marked by tide pool s. Tide pools are areas that are completely underwater at high tide but remain as pockets of seawater when the tide ebbs.
The intertidal zone can be hard-bottomed or soft-bottomed. A zone with a hard bottom is rocky. A zone with a soft bottom has silt or sand. Wetland s and marsh es are often soft-bottomed intertidal zones.
Different creatures have adapt ed to different types of intertidal zones. Hard-bottom zones often have barnacles and seaweed s, while soft-bottom zones have more sea plants and slow-moving creatures like ray s. Intertidal zones are marked by vertical zonation. Different organisms live in different zones in the tidal range, depending on how much water reaches them. This zonation can often be seen vertically, with dry plants near the top of the tidal zone and seaweeds near the bottom.
The intertidal zone can be broken into four major mini-zones. Thus, its tide-generating force is reduced by 3 , or about 59 million times less than the moon. The relationship between the masses of the Earth, moon and sun and their distances to each other play a critical role in affecting the Earth's tides.
Although the sun is 27 million times more massive than the moon, it is times further away from the Earth than the moon. Tidal generating forces vary inversely as the cube of the distance from the tide-generating object.
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