Why are the spring tides the highest each month?

Question

and i never understood how the moon and sun cause tides

Answer 1

if you had a VERY accurate spring scale, you'd see that your weight changed through a day.

however, since you eat, and ..... well .... maybe we ought to use a rock instead.

and over the course of a day, the weight of a rock will change, ever so slightly.

the rock, and you are attracted to the center of the earth.

that's the reason you have weight.

but the moon has some attraction also, and you are attracted to it as well.

when the moon is directly over your head, it attracts you, and the rock, and makes each weight less.

of course, you have to use a spring scale.

if you use a balance scale, the weights on the other side are also attracted, and there will not be a discernible difference.

on the other hand, if you see the moon low in the horizon, you're attracted slightly in that direction.  but that's harder to measure, and completely unnoticeable by our senses.

water does the same thing.

when the moon is overhead, it's attracted toward it.

the difference is that water can move.

and it does.

just as the moon exhibits attraction, so does the sun.

when the moon and sun are lined up, then the effect is slightly stronger, and it's called a spring tide.

(not to be confused with April, may, and June.)

when the sun and moon are at right angles, and we can see a semicircle, then the forces are fighting each other, the tides are lower, and it's called a neap tide.

OK, you might ask, but what about the other tides -- the ones when the moon is on the other side of the earth?

glad you asked.

perceptive of you.

you've always been told that the moon goes around the earth.

wrong.

well, very slightly wrong.

the moon and the earth orbit about a point that is the center of mass of the earth and moon.

consider, if you had 2 balls with a string between them.

you could twirl them around over your head.

however, suppose one ball was heavier than the other.

they'd still twirl, but the light ball would move in a large circle, and the heavy ball would move in a small circle.

that's what happens between the earth and moon.

gravity is the string.

the moon moves in a large circle, and the earth moves in a small circle.

have you ever heard of, seen, or tried, spinning a bucket of water over your head?

it really does work.

of course, you have to do it fairly fast.

and it slops, so you don't want a really full bucket.

BUT, for this discussion, the water tends to flow to the outside of the circle in which the bucket is traveling.

likewise, water piles up on the outside of the small circle that is the earth.

Answer 2

Below is an answer I gave to a similar problem:

Tides are caused by the gravitational attraction of the earth to the moon and to the sun.  Although the moon is a lot smaller than the sun, it is a lot closer to the earth; so the moon's gravitational effect on the tides is about three times that of the sun.

The highest tides ocur when the sun, the earth and the moon are all in line, and the gravitational attraction of the sun and the moon is aligned. These are called 'spring tides', and they happen during new moon (when the sun and the moon are on the same side of the Earth), and full moon (when the sun and the moon are opposite each other).  When the sun and the moon are at right angles, relative to the earth (during half moon), the tides are at their weakest, called 'neap tides'.  Also, during its orbit around the sun, the earth is closer to the sun at times; and during these times, the spring tides are at their highest; called 'king tides', ot technically 'perogee syzygy' tides - meaning 'closest in line'.

It is easy to understand why there are spring tides when the sun and the moom are on the same side and 'pull together'; but spring tide when the sun and the moon are pulling 'against each other' during full moon seems counter-intuitive:

Ignoring the effect of the sun for the time being; we discover that high tides ocurr on opposite sides of the earth at the same time.  This is also difficult to understand; surely if the tide is caused by the gravitational attraction of the moon, it is obvoius that the seas on the side closer to the moon would bulge out towards the moon. Why then, would there be a high tide on the opposite side? - You would think that on the side furthest away from the moon, the effect would be that the tide there should be lower, because of the bulge on the side nearest the moon.

The reason has to do with the fact that gravitational attraction  towards the moon is weaker on the side of the earth facing away from the moon.  In effect,  the seas closer to the moon are attracted towards it, but at the same time, the gravitational centre of the earth is attracted towards the moon MORE than the seas on the furthest side; and so the earth is 'pulled' away from those seas.

The net effect is that the seas closest to the moon are subject to a net pull TOWARDS the moon (relative to the earth), and the seas on the opposite side are subject to a net pull AWAY from the moon (relative to the earth).

Now bringing the sun into the equation, we can see why tides are highest at full moon:  Then, the seas facing away from the moon are pulled AWAY from the moon relaive the the earth; but at the same time are pulled TOWARDS the sun, relative to the earth.  The effect is reversed on the side facing the moon: net attraction TOWARDS the moon and AWAY from the sun.

Now it can be seen why tides are highest at full moon.

The effect is called tidal stretching, and is caused by the fact that gravitational attraction between two bodies decreases with the square of the distance between them. This has startling effects near very strong gravitational objects (the most powerful being a black hole) An object falling into a black hole would be infinitely stretched, because of the tidal effect.

Answer 3

Gravity keeps the moon in orbit around the earth and the earth around the sun.  In addition to orbiting, gravity pulls the water of the oceans toward the sun/moon.  When the moon is between the earth and sun, in a line, or very near a line, the added pulls of the sun and moon cause a spring tide

Answer 4

Spring tides are highest twice a month because twice a month the moon and the sun's combined gravitational pull on the earth is larger than any other time.

Spring tides occur when the earth, moon and sun are in a straight line.  That occurs during both the new and full moon phases.  Since every month has one full moon and one new moon (sometimes there are two full or new moons in one month), there are two spring tides each month.

The moon's gravity and to a lesser extent the sun's gravity cause tides.

There are also neap tides which also occur twice each month.  These are lower than normal tides.  They occur during the first and last quarter phases of the moon.

That is when the sun and moon are at right angles to the earth.

To see a good diagram of this, go to:

http://www.cartage.org.lb/en/themes/scie...