Why do we have high and low tides?

Answer 1

Tides are caused primarily by our moon's gravity. While the moon takes a whole month to orbit the earth, the earth turns on its axis once per day. So the earth moves through the tidal bulges of water produced by the moon's gravity.

Answer 2

First, recall Kepler's Third Law of Orbital Motion, or else work out the orbital speed of an object in a circular orbit by setting centripetal force equal to gravitational force and solving for velocity. Either way, you discover the that velocity of a small object in orbit has to be faster in close to the object it is orbiting, and slower further away. So now think about a large object (i.e. one with an appreciable diameter) in a circular orbit. The whole thing moves at orbital speed for the distance that its centre of mass is at. But some parts of it are appreciably closer to the central object, and some are appreciably further away. That means that the bits that are closer are moving slower than circular-orbit speed for the distance they are at. Gravity is stronger than what would keep them in the orbit they are in and tends to curve their path more, so they tend to fall towards the centre as though they were at the apapsis (high point) of a slower, elliptical orbit. On the other side you find bits of the large body that are further away from the centre than the centre of mass, moving slightly faster than circular-orbit speed at their actual distance. For them, gravity is slightly weaker than what would give them a circular path at their current distance and speed and tends to curve their path less. They tend to rise away from the centre as though at the periapsis (low point) of a faster, elliptical orbit. The result is that one bulge of material rises towards the body that this body is orbiting, on the face towards it, and another rises on the opposite face, away from the body that the body is orbiting. These are the two tidal bulges. The rise to the point where either elastic forces in the orbiting body or the gravitational disequilibrium of its distorted surface provide an equal countervailing force.

It doesn't matter if the orbit is not circular: any extended object moving through a gravitational field feels gravity more strongly on the side nearer to the gravitating body than at its centre of mass, and less strongly at the side further from the gravitating body, so its near parts tend to curve more towards the gravitating body, and its further parts less, than its trajectory producing tidal strain.

Now, Earth can be considered to be orbiting in the Sun's gravity, and also in the Moon's gravity (never mind the the centre of that orbit is not at the Moon, it doesn't matter). So Earth tends to get a tidal bulge pointing towards the Moon and one pointing away from the Moon, and a smaller one (1/3 the height) pointing towards the Sun and another one pointing away from the Sun. These get displaced from their positions by Earth's rotation, but that's a bit of a tangent. The important thing is that both the ocean and the solid material of the Earth feel the tidal strain, but the oceans respond to it much faster. If Earth were non-rotating the material of the mantle would conform to the tidal bulges, but at Earth's current rotation rate it doesn't get time to. So the tides in the ground are smaller than the tides in the ocean, and not quite in phase with them.

Any particular point on the Earth rotates into and back out of the tidal bulges. and the ocean raises and falls, but the land doesn't get time to rise or fall as much. Thus the oceans tend to rise and fall with respect to the land. The atmosphere does too, as you can see if you look at a graph of frequent measurements of the atmospheric pressure.

Now, it turns out that the range of the lunar tide on Earth is only about four feet, and the solar tide is a third of that. What gives us the much larger tidal ranges that we actually see in a lot of places is that the solar and lunar tides act as a periodical driver, pushing and pulling water on a regular schedule. In places where the period of these tides corresponds to the natural resonant frequency for waves in a "basin" constrained by the landform, a sort of tidal slosh builds up by resonance. And that gives you the high tides and low tides.

Answer 3

Tides are caused primarily by our moon's gravity. While the moon takes a whole month to orbit the earth, the earth turns on its axis once per day. So the earth moves through the tidal bulges of water produced by the moon's gravity.

Answer 4

First, recall Kepler's Third Law of Orbital Motion, or else work out the orbital speed of an object in a circular orbit by setting centripetal force equal to gravitational force and solving for velocity. Either way, you discover the that velocity of a small object in orbit has to be faster in close to the object it is orbiting, and slower further away. So now think about a large object (i.e. one with an appreciable diameter) in a circular orbit. The whole thing moves at orbital speed for the distance that its centre of mass is at. But some parts of it are appreciably closer to the central object, and some are appreciably further away. That means that the bits that are closer are moving slower than circular-orbit speed for the distance they are at. Gravity is stronger than what would keep them in the orbit they are in and tends to curve their path more, so they tend to fall towards the centre as though they were at the apapsis (high point) of a slower, elliptical orbit. On the other side you find bits of the large body that are further away from the centre than the centre of mass, moving slightly faster than circular-orbit speed at their actual distance. For them, gravity is slightly weaker than what would give them a circular path at their current distance and speed and tends to curve their path less. They tend to rise away from the centre as though at the periapsis (low point) of a faster, elliptical orbit. The result is that one bulge of material rises towards the body that this body is orbiting, on the face towards it, and another rises on the opposite face, away from the body that the body is orbiting. These are the two tidal bulges. The rise to the point where either elastic forces in the orbiting body or the gravitational disequilibrium of its distorted surface provide an equal countervailing force.

It doesn't matter if the orbit is not circular: any extended object moving through a gravitational field feels gravity more strongly on the side nearer to the gravitating body than at its centre of mass, and less strongly at the side further from the gravitating body, so its near parts tend to curve more towards the gravitating body, and its further parts less, than its trajectory producing tidal strain.

Now, Earth can be considered to be orbiting in the Sun's gravity, and also in the Moon's gravity (never mind the the centre of that orbit is not at the Moon, it doesn't matter). So Earth tends to get a tidal bulge pointing towards the Moon and one pointing away from the Moon, and a smaller one (1/3 the height) pointing towards the Sun and another one pointing away from the Sun. These get displaced from their positions by Earth's rotation, but that's a bit of a tangent. The important thing is that both the ocean and the solid material of the Earth feel the tidal strain, but the oceans respond to it much faster. If Earth were non-rotating the material of the mantle would conform to the tidal bulges, but at Earth's current rotation rate it doesn't get time to. So the tides in the ground are smaller than the tides in the ocean, and not quite in phase with them.

Any particular point on the Earth rotates into and back out of the tidal bulges. and the ocean raises and falls, but the land doesn't get time to rise or fall as much. Thus the oceans tend to rise and fall with respect to the land. The atmosphere does too, as you can see if you look at a graph of frequent measurements of the atmospheric pressure.

Now, it turns out that the range of the lunar tide on Earth is only about four feet, and the solar tide is a third of that. What gives us the much larger tidal ranges that we actually see in a lot of places is that the solar and lunar tides act as a periodical driver, pushing and pulling water on a regular schedule. In places where the period of these tides corresponds to the natural resonant frequency for waves in a "basin" constrained by the landform, a sort of tidal slosh builds up by resonance. And that gives you the high tides and low tides.

Answer 5

well, the heights fluctuate overtime due to the 24 hour and 50 minute movement of the moon around the earth in a series of time