###### Matt Jones

M.Ed., George Washington University
Dept. chair at a high school

Matt is currently the department chair at a high school in San Francisco. In his spare time, Matt enjoys spending time outdoors with his wife and two kids.

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# Tides

Matt Jones
###### Matt Jones

M.Ed., George Washington University
Dept. chair at a high school

Matt is currently the department chair at a high school in San Francisco. In his spare time, Matt enjoys spending time outdoors with his wife and two kids.

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Ocean tides are the rising and falling of the sea due to variations in the gravitational pull of the moon on opposite sides of the Earth. Tides are a type of wave with regular frequencies and periods which echo the motion of the moon.

You're probably aware that the ocean rises and falls twice a day and when it rises completely we call it high tide and when it's down at its lowest level we call that low tide. You're probably also aware that this tide is due to the force of gravity and in this case it's the force of the largest object close to us which is the moon pulling on the side of the earth that the moon is closest to so let's look at how that works so here's the moon, here's the earth and the earth again is round but the gravitational force of the moon is going to pull on the earth. Now the, the earth is mostly rock its outer crust but it does have a lot of liquid around it like the oceans and the oceans are flexible, malleable and they're actually going to be bulging out in this direction towards the moon and it turns out they're actually bulging out on the opposite side of the moon to create this funny bulge so the earth is actually not completely spherical it's actually a little bit of an oval shaped due to the gravitational force of the moon.

Now the moon is not the only large object around, that has that influences our tides, there's another large object called the sun right? And let's say the sun is over here, now the sun is much farther away from the moon so the gravitational force the sun applies on to earth is much weaker than the moon but if we have the sun pulling and the moon pulling that's going to create stronger gravitational force and we're going to see larger tides, tides rising higher, we call that a spring tide. Now spring tide obviously means that it occurs in spring well no it doesn't, has nothing to do with the seasons but it has to do with the cycle of the moon, any time the moon is completely behind the earth in terms of a new moon or over here, this would be a full moon, this remember this side would be dark so we wouldn't see the moon at all okay? These are examples of spring tides where during the lunar cycle the sun and the moon are aligned and they strengthen the gravitational force by acting together to make very high tides and very low, low tides okay.

There's another time when the moon is perpendicular to the sun, now what if we looked at the moon, sun would be shinning on this side of the moon I'm sorry that side is dark, sun is shinning over here and this side is dark and we see a half moon so half way to the lunar cycle, this is called a neap tide. And these are going to be the lowest of the high tides and the least of the low tides going down the least amount because in this case we have the sun and the moon pulling at 90 degree angles to each other so they are not acting together they're acting a little bit in opposition and the tides are reduced. Since the moon is still the stronger of the two forces, the moon will still cause the high tides in these areas but the sun is not helping the moon with those tides it's actually working against it, so these are examples of different types of tides that we get and it helps explain the moon and the sun and how they influence our tides.