Hey guys!! I hope everyone is doing great…
Let me give a quick introduction to what we are looking at in this post.
The occurrence of tides in our oceans is shrouded in mystery. And just like any educated man would do, we rely on the experts in this particular field to provide some answers. These experts measure the different quantities associated with the tides, and they come up with a theory, an explanation for why the measurements are such. The problem is, we only have different theories about tides as of now. And none of these is actually accepted as the best explanation or any such thing.
But we did accept some theories and made them popular. One such theory that was popular long ago turns out to be famous and incorrect. Of course as other experts comment against it, its fame decays. But that didn’t stop it from coming up as the first search result when I googled “Why do tides occur”. Till now, I have found three different explanations for tides on different websites which I have mentioned in references. I need to study them properly before making any comment obviously. So I’ll leave these for the next post.
Today, however, I’ll clarify on the old, incorrect and yet popping-up-first-on-google explanation.
Also, I noticed that the flat earthers are quite happy that we don’t have the right explanation, so they are promoting their own theories for the occurrence of tides, lol. I am hurt that I fell into reading one of their articles. I was desperate to seek a proper explanation for tides you see. I was on quora and I also had to read some dude giving a wrong explanation in an apparently fake science journal. I can’t let this be the talk of the day, so I’ll restrict them to links that you can check out.
Let’s begin…
First, allow me to tell you that this blog series is a little bit more personal than recent ones. This topic will require a lot of explaining... So this has to be a series. It’s like a mini-series inside a big series actually, since we are discussing ocean energy.
I discussed ocean tides briefly in earlier posts, but I want this post to help with clarity for new comers, and also the flat earthers. So I'll tell you about it, right from the beginning. And I'll provide references for every point I make. This series might take two to three posts. And if you are wondering how come flat earthers succeeded in wasting my time. I'll tell you the details later. For starters, they can't tolerate the idea of a spherical earth rotating around it's own axis, which turns out to be crucial for tides to occur.
Introduction to Tides:
Definition:
An ocean tide refers to the cyclic rise and fall of seawater. Tides are caused by slight variations in gravitational attraction between the Earth and the moon and the Sun in geometric relationship with locations on the Earth's surface. Tides are periodic primarily because of the cyclical influence of the Earth's rotation.
Source
Almost all the kinds of renewable energy sources are quite randomly available. For example the wind blows slower and faster on it's own. Waves in ocean are available quite randomly, thanks to the wind. Such small changes are not regular, and they can't actually be predicted. We calculate their availability by taking average over a period of time. But that isn't really necessary with sunlight. I mean we do take average availability of sunlight to check for economics and efficiency but that's not the case here. I'm saying that we know exactly when the sun will be on our side of earth, when will it be day, and when it will be night. that's regular, right? And we can easily guess the availability throughout the seasons. As in we know that summers will always be hot and bright, winters will always be cold and foggy, and so on. These things are predictable. Tides are one such form of energy.
One very important feature of tides is that they are a regular, and predictable change. You can even say they are as regular as day and night. We'll talk about the flat earthers and fake science articles later. That will take more than one post, lol.
So, let's see what factors are responsible for the occurrence of tides. There are two simple factors that cause them.
- The Rotation of earth around it's axis.
- The Gravitational Forces between earth, moon, and sun. The force between earth and moon being most dominant.
Let's discuss these in a bit detail first.
1. The Rotation of earth
Most places "measure" two high tides and two low tides per day. Well, that's because earth rotates around it's own axis. Dear flat earthers, yes, it really does. Nope, it doesn't matter what you or I think, because it does rotate. Earth spinning around it's own axis is what really causes day and night, and also the tides.
2. Gravitational pull from The Moon and The Sun
It's not like the theory of relativity can't explain this phenomenon, but it would make this post quite complicated. Newtonian mechanics is easy, and even kids understand it very well. So let's go with it.
Whereas the rotation of earth determines the timing of tides, the gravitational pull from the moon and the sun determines how big or small the tidal bulges on each side of earth are. Of course we can't go where the bulge has occurred to measure it (the wind and waves can easily mess with such measurements), but we can stay at shore and measure how much water level has dropped and raised during the tide's occurrence. This is called the tidal range. It is the difference between the water levels during a high tide, and a low tide.
The earth, moon and sun system being in a straight line results in more gravitational pull, and hence results in a bigger tidal range. Tides that occur during this period is called the spring tides.
If earth moon and sun are located such that, the lines drawn from earth to moon and earth to sun make kind of a right angle with each other, the effect of moon's gravitational pull is diminished, and we have a smaller tidal range. Tides that occur during this period are called the neap tides.
That's all, now let's get a clear idea about how this phenomenon really happens. I am stressing on clarity because there are some misconceptions about this in the science community as well, not just the flat earth society or fake science journals. Let's discuss those of the science community first, because they are reasonable, lol. The first time I read about the occurrence of tides, I was provided with this old explanation (misconception) as well.
There are two categories of explanations, I'll simply call them as the old explanation and the new ones. I don't really know who gave these and when. I can only give you the links to some educational websites. And the old explanation is real popular, and it is very slightly wrong (compared to a flat earth theory, lol).
The Old Explanation:
This is actually a very easy one. And being easy, also makes it easy for us to imagine.
If we ignore the sun for a while, our entire process of tide formation can be explained in three simple steps:
- The moon pulls water on earth surface towards it due to it's gravitational pull.
- The earth being much heavier than the moon, shifts very slightly towards the moon.
- The water on the other side of earth is too much farther from the moon to be pulled towards it, and hence looks like a bulge beacause the earth has slightly shifted towards the moon.
Search it, and you'll find this explanation all over the internet. Here are some such links.2,3,
We need to consider three important factors if we want to correct this old explanation that we just discussed.
- frequency of tides.
- rotation of earth around it's own axis.
- rotation of moon around earth.
Now let's talk about each of these one by one.
Frequency of tides
Most places on earth experience two high tides, and two low tides per day. Such tides are called semi-diurnal tides. And this is what I meant when I said tides are a regular and predictable change. Some places have just two tides per day (called diurnal tides).
This regularity can be "measured" (not just theorized), every 24 hours and 50 mins, which is what we call a Lunar day, or more simply, (in our reference frame) time taken by the moon to return to the same position in sky. And that's what makes tides predictable.
The Spin of The Earth and The Revolution of The Moon...
Nope, I won't argue that the earth spins anymore, lol.
Now, let's understand some facts.
The moon takes 27.32 days to make one revolution around the earth (say one full moon to the next). And this means, 1 lunar day (takes time period of 24 hours and 50 minutes), doesn't mean that the moon has revolved the earth. It only means that the earth has rotated around it's own axis once ( which takes 24 hours) and bit more (which accounts for the additional 50 minutes in the lunar day).
If earth was stationary, and never revolved around itself - instead of having tides twice daily, we would have them twice every 27.32 days. The earth's spin, causes the moon to face a huge mass of water, twice. And that causes two high and low tides per day in most places (near the equator).
But also, according to the old explanation, the earth get pulled towards the moon, so that the bulge appears on the other side of earth as well, right? I guess now I have a good question. I also have the answer for you, so just relax and enjoy reading.
Since the high and low tides occur at most twice a day, as per our old explanation, I have to assume that the earth gets pulled towards the moon, very slightly, twice a day. I really hope you get this part clearly, scroll up if you have any doubts.
Now, As per our knowledge of gravity, we know that masses can only attract each other, and not repel, right? So what our old explanation is actually saying is, the earth gets pulled towards the moon twice a day!!
Can this distance by which our earth moves closer to moon, be recovered? Gravity only attracts, it never repels. Can the distance between earth and moon be increased again, in order to keep it constant? And because tides happen everyday, this "shifting towards the moon" has to go on and on without any means of recovery at all. The question is open to all physicists. See if you can support the old explanation yourself.
Well, for a moment let's assume this happens, the change in distance between earth and moon should have been noticed by now. I searched the web again, to see if this distance changes over any period of time, ever. And I found that it does, but the reasons are entirely different. I know this is a bit confusing for you, I'm sorry. But you can always ask any questions in the comments. Or you can read and understand this point by point later, when ever you find time. For now, please allow me to bust a wrong theory.
- The earth and moon rotate as a system of two masses. It does appear that the moon rotates around the earth, but that's not precisely the case. For those of you new to this, imagine anything that rotates, and observe the one point around which this happens. That's the center of mass of that body. Our Earth as well as the moon actually rotate around the center of mass of the system, which lies inside the earth. And that is why it just appears that only the moon is rotating around the center of mass. The fact is earth rotates around this center of mass as well. But this won't do as an explanation for changing distance between earth and moon.
The distance of bodies from the center of mass of the system is always constant, so how can we say earth gets pulled towards the moon? We can't.
- The moon orbits around the earth is a slightly elliptical orbit. So we can say the distance between earth and moon changes over a 27.32 days. But still, we just can't say earth gets close to the moon every day, can we?
So my conclusion on this topic is as follows:
the slight change in distance between earth and moon seems entirely irrelevant to the process of tide formation.
The rotation of earth around the center of mass of the earth moon system takes a lot of time (more than 27 days). Also the moon having an elliptical orbit doesn't help since it takes almost a month to complete. So this can't be seen as a reason for distance between earth and moon decreasing twice every day.
And that, my dear readers, is my explanation that the old explanation isn't a very correct explanation, lol. Anyways, the rest of the story will be in the next post, I really wished I could keep this short, but I wanted things to be as easy and clear as possible for you. Thank you very much for your time. And please ask any questions you have, irrespective of what shape and size of earth you prefer to believe in, lol.
See you real soon. Take Care, and have fun.
References:
Some important material I read to prepare this article: 4, 5, 6, 7,
The new ways of explaining the occurrence tides: 8, 9, 10
Note: The gifs, no matter how crappy, they are still mine. My animation using the easiest animation software synfig is still crappy, I know. I just started learning it. lol.
Links to Earlier Posts in the series on Ocean Energy:
1. Basics of Ocean Energy
2. Energy from the Ocean waves - Part 1
3. Energy from Ocean Waves - Part 2: Wave Energy Devices
4. Energy from Ocean Waves - Part 3: Wave Energy Devices continued and a simple introduction to Ocean Tides