CSET Requirement 2.2b: Describe the mechanisms that cause wave action and tides.
WAVES
Waves are the forward movement of the ocean's water due to the oscillation of water particles by the frictional drag of wind over the water's surface.Waves have crests (the peak of the wave) and troughs (the lowest point on the wave). The wavelength, or horizontal size of the wave, is determined by the horizontal distance between two crests or two troughs. The vertical size (height) of the wave is determined by the vertical distance between the two. Waves travel in groups called wave trains.
It is important to note that while it appears that water is moving forward, only a small amount of water is actually moving. Instead, it is the wave’s energy that is moving and since water is a flexible medium for energy transfer, it looks like the water itself is moving. In the open ocean, the friction moving the waves generates energy within the water. This energy is then passed between water molecules in ripples called waves of transition. When the water molecules receive the energy, they move forward slightly and form a circular pattern.
As the water’s energy moves forward toward the shore and the depth decreases, the diameter of these circular patterns also decreases. When the diameter decreases, the patterns become elliptical and the entire wave’s speed slows. Because waves move in groups, they continue arriving behind the first and all of the waves are forced closer together since they are now moving slower. They grow in height and steepness. When the waves become too high relative to the water’s depth, the wave’s stability is undermined and the entire wave topples forming a breaker.
It is important to note that while it appears that water is moving forward, only a small amount of water is actually moving. Instead, it is the wave’s energy that is moving and since water is a flexible medium for energy transfer, it looks like the water itself is moving. In the open ocean, the friction moving the waves generates energy within the water. This energy is then passed between water molecules in ripples called waves of transition. When the water molecules receive the energy, they move forward slightly and form a circular pattern.
As the water’s energy moves forward toward the shore and the depth decreases, the diameter of these circular patterns also decreases. When the diameter decreases, the patterns become elliptical and the entire wave’s speed slows. Because waves move in groups, they continue arriving behind the first and all of the waves are forced closer together since they are now moving slower. They grow in height and steepness. When the waves become too high relative to the water’s depth, the wave’s stability is undermined and the entire wave topples forming a breaker.
Tides
Tides are considered the heartbeat of our planet’s oceans. They are the periodic rise and fall of the earth’s bodies of open water, and are a result of the gravitational pull of the moon and sun on the earth, as well as the perpetual spinning rotation of the earth itself.
By far the largest influence is the gravitational effect of the moon as it pulls the water toward itself, making a bulge on the surface of the ocean at the side of the moon (lunar tide). The ocean is constantly moving from high tide to low tide, and then back to high tide. There is about 12 hours and 25 minutes between the two high tides.
When the sun and moon are aligned, in which the moon is full or new, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. When the sun and moon are not aligned (forming a 90 degree angle), in which the moon is at its first or third quarter, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides.
It interesting to note, and always discussed in classrooms, that the sun also has a part to play with tide formation. But since the sun is about 93 million miles away, its gravitational force is smaller, as compared to the moon, and so the sun's role is greatly decreased. However, when the three are aligned (Earth, Sun and Moon), the gravitational pull of the sun adds to that of the moon causing maximum tides.
We have to consider the fact that the Earth, Moon and the Sun are not static. Earth rotates on it's axis as it revolves around the Sun, and the Moon has its own axial and revolutionary movement. Because Earth rotates on its axis, the Moon completes one orbit in our sky every 25 hours (not to be confused with moon's 27 day orbit around the earth), we get two tidal peaks as well as two tidal troughs. These events are separated by about 12 hours. Since the moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes.
You have to understand how these orbits play out in tide formation. Think about the effect the Moon has on Earth everyday as it creates a drag with all that water that's being displaced at both ends of the globe. As a consequence of tidal interactions with the Moon, the Earth is slowly decreasing its rotational period. The Moon is gradually receding from the Earth into a higher orbit, and calculations suggest that this would continue for about fifty billion years. By that time, the Earth and Moon would become caught up in what is called a "spin–orbit resonance" or "tidal locking" in which the Moon will circle the Earth in about 47 days (currently 27 days), and both Moon and Earth would rotate around their axes in the same time, always facing each other with the same side.
By far the largest influence is the gravitational effect of the moon as it pulls the water toward itself, making a bulge on the surface of the ocean at the side of the moon (lunar tide). The ocean is constantly moving from high tide to low tide, and then back to high tide. There is about 12 hours and 25 minutes between the two high tides.
When the sun and moon are aligned, in which the moon is full or new, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. When the sun and moon are not aligned (forming a 90 degree angle), in which the moon is at its first or third quarter, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides.
It interesting to note, and always discussed in classrooms, that the sun also has a part to play with tide formation. But since the sun is about 93 million miles away, its gravitational force is smaller, as compared to the moon, and so the sun's role is greatly decreased. However, when the three are aligned (Earth, Sun and Moon), the gravitational pull of the sun adds to that of the moon causing maximum tides.
We have to consider the fact that the Earth, Moon and the Sun are not static. Earth rotates on it's axis as it revolves around the Sun, and the Moon has its own axial and revolutionary movement. Because Earth rotates on its axis, the Moon completes one orbit in our sky every 25 hours (not to be confused with moon's 27 day orbit around the earth), we get two tidal peaks as well as two tidal troughs. These events are separated by about 12 hours. Since the moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes.
You have to understand how these orbits play out in tide formation. Think about the effect the Moon has on Earth everyday as it creates a drag with all that water that's being displaced at both ends of the globe. As a consequence of tidal interactions with the Moon, the Earth is slowly decreasing its rotational period. The Moon is gradually receding from the Earth into a higher orbit, and calculations suggest that this would continue for about fifty billion years. By that time, the Earth and Moon would become caught up in what is called a "spin–orbit resonance" or "tidal locking" in which the Moon will circle the Earth in about 47 days (currently 27 days), and both Moon and Earth would rotate around their axes in the same time, always facing each other with the same side.