How does moon control tides

However, the presence of land masses stopping the flow of water, the friction in the oceans and between oceans and the ocean floors, the rotation of Earth, the wind, the variable depth of the ocean, and other factors all complicate the picture.

This is why, in the real world, some places have very small tides while in other places huge tides become tourist attractions. The rubbing of water over the face of Earth involves an enormous amount of energy. Over long periods of time, the friction of the tides is slowing down the rotation of Earth. Our day gets longer by about 0. That seems very small, but such tiny changes can add up over millions and billions of years. Figure 5. Thus, some other spin motion must speed up to take the extra angular momentum.

The details of what happens were worked out over a century ago by George Darwin , the son of naturalist Charles Darwin. George Darwin see Figure 5 had a strong interest in science but studied law for six years and was admitted to the bar.

However, he never practiced law, returning to science instead and eventually becoming a professor at Cambridge University. He specialized in making detailed and difficult mathematical calculations of how orbits and motions change over geologic time.

What Darwin calculated for the Earth-Moon system was that the Moon will slowly spiral outward, away from Earth. This variation creates the differential forces or tidal forces that in turn cause tides. The tidal forces of the Moon are much stronger than the Sun's because it is so much closer to our planet , causing a much greater variation in the gravitational force from one location to another.

The Sun's gravitational force, on the other hand, varies much less because the Sun is so far away. However, the variation between high and low tide is very different from place to place. It can range from almost no difference to over 16 meters over 50 feet.

This is because the water in the oceans is constrained by the shape and distance between the continents as well as varying ocean depths. As a result, the tides behave more like water sloshing around in an oddly shaped bathtub than in a smooth and even basin.

In some places, the water flows freely and quickly, while in other areas, where the water has to pass through narrow channels, it moves more slowly. Tides are one of the most reliable phenomena in the world, and we know that they move in and out around twice a day, but not exactly.

So, why is that? A day on Earth is the time it takes our planet to spin once around its own axis in relation to the Sun. This is known as a solar day, and it lasts around 24 hours.

However, the time it takes Earth to reach the same position in relation to the Moon is, on average, 24 hours and 50 minutes, known as a lunar day. Because the tidal force of the Moon is more than twice as strong as the Sun's, the tides follow the lunar day, not the solar day. It takes half a lunar day, on average 12 hours and 25 minutes, from one high tide to the next, so we have high and low tides nearly twice a day. According to the National Ocean Service , there are some exceptions to the main rule of two tides every lunar day.

Along the coastline of the Gulf of Mexico, there is only one tide per day due to the local shoreline topography, among other things. This tidal cycle is called a diurnal cycle, as opposed to the normal semidiurnal cycle, where diurnal means daily and semi means half.

While in theory, the tidal bulges follow the Moon's position on its orbit around the Earth, the depth and shape of the ocean and the distance between continents are also important in determining when the tide rolls in and out. In much of the rest of the world, the variation is only a few feet up and down with each high and low tide. Ellie Webb How does the moon affect the tides?

Grant Petty. 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.

These two bulges explain why in one day there are two high tides and two low tides, as the Earth's surface rotates through each of the bulges once a day. The Sun causes tides just like the moon does, although they are somewhat smaller. When the earth, moon, and Sun line up—which happens at times of full moon or new moon—the lunar and solar tides reinforce each other, leading to more extreme tides, called spring tides.

When lunar and solar tides act against each other, the result is unusually small tides, called neap tides. There is a new moon or a full moon about every two weeks, so that's how often we see large spring tides. When the gravitational pull of the Sun and moon are combined, you get more extreme high and low tides. This explains high and low tides that happen about every two weeks.

Note: this figure is not to scale. The Sun is much bigger and farther away. Wind and weather patterns also can affect water level. Strong offshore winds can move water away from coastlines, exaggerating low tides.

Onshore winds can push water onto the shore, making low tides much less noticeable.