Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jccc on 18/01/2015 15:16:35
-
Tides raise and fall, where comes the energy? Why the moon speed not decrease faster?
-
You're right that the energy comes from the Moon-Earth system (at least for the lunar tides). The Moon is slowing down ever so slightly, and moving away from the Earth (to maintain angular momentum). The Earth's rotation is also slowing (day is getting longer). In a few billion years the day will be longer than the month, and the Moon will start falling towards the Earth.
-
You're right that the energy comes from the Moon-Earth system (at least for the lunar tides). The Moon is slowing down ever so slightly, and moving away from the Earth (to maintain angular momentum). The Earth's rotation is also slowing (day is getting longer). In a few billion years the day will be longer than the month, and the Moon will start falling towards the Earth.
Sounds very true. But can you put it in real numbers? Move so much water all the time, few years should be enough to change the orbit a lot.
-
See here for a more in depth explanation:
http://en.wikipedia.org/wiki/Tidal_acceleration
-
Edit--I misspoke in my previous post:
While its angular velocity decreases, the actual orbital velocity of the Moon is increasing. As it does so, the Moon's orbital distance is increasing as well. Both at the expense of the Earth's rotational speed.
-
Let’s get more fundamental.
Simplistically, the moon is orbiting the Earth. It is following a curved trajectory, so it is accelerating. Acceleration requires energy; gravity is the “force” involved. If gravity is constantly providing the energy for the moon’s acceleration, why is gravity not becoming weaker?
-
Sounds very true. But can you put it in real numbers? Move so much water all the time, few years should be enough to change the orbit a lot.
It's unrealistic to expect all physicists and everyone familiar with physics to know how to make those calculations off hand. If you want to read about them then I recommend that you pick up a text on the subject and do the work for yourself. E.g. see
Fundamentals of Geophysics by Lowrie W. page 56
http://bookzz.org/book/1022791/0e1105
-
I suspect solar energy partially transfer into tidal energy. Maybe?
-
Only insofar as the solar energy keeps our oceans liquid, allowing for much greater tidal displacement.
I think you might be think about tides the wrong way--the Moon isn't dragging the water around the Earth--the Moon and Earth are orbiting each other (on a period of about a month). The two tides are on the side closest to the Moon, where the gravity of the Moon is pulling the ocean slightly more than it's pulling the Earth, and on the farthest side of the Earth, where the Moon is pulling the Earth more than the ocean. The tides are essentially stationary from the Moon's perspective, and the Earth is rotating on its axis such that it looks like the ocean is moving, but really its just the Earth moving (just like the Moon, Sun and stars look like they go around the Earth one a day). Does that make sense?
-
Solar energy per-se doesn't impact the tides, but sun's gravity does.
Earth is closest to the sun in the winter (Northern Hemisphere). So, winter days with a full moon (sun and moon on opposite sides of the earth) or a new moon (sun and moon on the same side of the earth) will have the highest and lowest tides.
-
Fish chase warm water, may help a bit on tide.
-
Fish chase warm water, may help a bit on tide.
Caw fart can cause global warming. Right?
-
The tides on earth are a weak form of tidal force. Consider when two gravitational fields intersect and cancel out. This is equivalent to saying that the fields cancel at the centre of a mass. If the point where the fields cancel is below the surface of one of the objects this will accrete any loose matter from the surface and any atmosphere.
-
Look back, science always follow mainstream scientists believes.
Look around, so so so so.
"If you can't explain it to a six year old, you don't understand it yourself." – Albert Einstein
BS
-
Look back, science always follow mainstream scientists believes.
That's an extremely ignorant statement based on a total lack of knowledge of the field of physics. If you followed the advice that I've given you over the months you'd learn why that statement is so wrong.
Look around, so so so so.
Okay. Let's look around and see what we find. Consider the following article
Energy is Not the Ability to Do Work by Robert L. Lehrman, The Physics Teacher, 11, 15, (1973).
Online at http://www.loreto.unican.es/Carpeta2012/TPT(Lehrman)WorkEnergy.pdf
Now look at Wiki
http://en.wikipedia.org/wiki/Energy
Because energy is defined as the ability to do work on objects..
All throughout the literature you'll find physicists disagreeing with each other. Most college general physics textbooks claim that energy is defined as the ability to do work. However famous physicists such as Sheldon Glashow and Richard Feynman state that energy cannot be defined at all.
Consider the following
In Newtonian Mechanics, A.P. French wrote [3]
Of all the physical concepts, that of energy is perhaps the most far-reaching. Everyone, whether a scientist or not, has an awareness of energy and what it means. Energy is what we have to pay for in order to get things done. The word itself may remain in the background, but we recognize that each gallon of gasoline, each Btu of heating gas, each kilowatt-hour of electricity, each car battery, the wherewithal for doing what we call work. We do not think in terms of paying for force, or acceleration, or momentum. Energy is the universal currency that exists in apparently countless denominations.
The above remarks do not really define energy. No matter. It is worth recalling once more the opinion that H.A. Krammers expressed: “The most important and fruitful concepts are those to which it is impossible to attach a well-defined meaning.” The clue to the immense value of energy as a concept lies in its transformation. It is conserved – that is the point. Although we may not be able to define energy in general, that does not mean that it is only a vague, qualitative idea. We have set up quantitative measures of various specific kinds of energy: gravitational, electrical, magnetic, elastic, kinetic, and so on. And whenever a situation has arisen in which it seemed that energy disappeared, it has always been possible to recognize and define a new form of energy that permits us to save the conservation law. And conservation laws, as we remarked at the beginning of Chapter 9, represent one of the physicist’s most powerful tools for organizing his description of nature.
Regarding its general application in physics, in his text Thermal Physics Daniel V. Schroeder wrote
To further clarify matters, I should really give you a precise definition of energy. Unfortunately, I can't do this. Energy is the most fundamental dynamical concept in all of physics, and for this reason, I can't tell you what it is in terms of something more fundamental. I can, however, list the various forms of energy - kinetic, electrostatic, gravitational, chemical, nuclear - and add the statement that, while energy can often be converted from one form to another, the total amount of energy in the universe never changes. This is the famous law of conservation of energy. I sometimes picture energy as a perfectly indestructible (and unmakable) fluid, which moves about from place to place but whose total never changes. (This image is convenient but wrong - there simply isn't any such fluid).
The journal American Journal of Physics have many examples of physicists attempting to prove long held beliefs to be wrong. Most of them make mistakes due to a missing point which is very hard to find. Those are often disproved in later editions by other physicists.
So your claim that science always follow mainstream scientists believes is total nonsense.
-
If gravity is constantly providing the energy for the moon’s acceleration, why is gravity not becoming weaker?
There is no need to provide energy to keep the moon in orbit.
Conservation of energy ensures that the existing gravitational potential energy of the Moon is exchanged very precisely with the kinetic energy of the Moon as it moves on its elliptical orbit around the Earth, month after month.
The strength of the gravitational force is determined by the masses of the two objects, and their distance. If the mass of Earth and Moon remains constant, as does the average orbital radius, then the gravitational force will remain constant.
[Apologies if I have missed some subtlety in the comment.]
-
Where does the energy come from ? The initial rotational energy was in the gaseous cloud from which the solar system condensed which had a degree of rotation relative to the rest of the universe.
See Mach, Einstein, Newton, ether etc rotational energy is a big puzzle
-
Where does the energy come from ? The initial rotational energy was in the gaseous cloud from which the solar system condensed which had a degree of rotation relative to the rest of the universe.
See Mach, Einstein, Newton, ether etc rotational energy is a big puzzle
Nice response. I wasn't quite sure what he was looking for so I ignored the original question. All systems of objects in the universe have energy which originated elsewhere in he universe. Exactly where cannot be said. For example: the energy of the earth moon system partly came from where the moon originated from.
-
Surely all the energy originated from whatever existed before the big bang. If this was a singularity this implies that black holes can explode. I don't know exactly how that would work. The energy would have evolved from this state with quantum mechanics determining how it developed and where it was directed. This is also where chaos theory comes in.
-
Surely all the energy originated from whatever existed before the big bang.
Not only is that not necessarily so but its not even the current hypothesis of the origin of energy in the universe. The total amount of the universe has been postulated to be zero from the beginning of the universe back to the big bang. This can happen because the total amount of gravitational potential energy is negative while the total amount of rest energy and kinetic energy is positive. The sum is they postulated to be zero. Of course its much more complicated than that since there are many different forms of energy but this gives the general idea.
If this was a singularity this implies that black holes can explode.
Hawking has already theorized that black holes can explode anyway.
-
Before we surely understand why is electron not stick to proton, we are nice talkers.
-
Before we surely understand why is electron not stick to proton, we are nice talkers.
We as physicists understand it quite well. Laymen such as yourself don't understand it. However its only important for those who use it to understand it. This is again another example of how your choice of not learning physics in a straightforward, i.e. textbook, manner is causing you problems. You're trying to grasp sub atomic/quantum phenomena using macroscopic/Newtonian mechanics. There is no meaning for an electron to "stick" to an electron in quantum mechanics. Read book on math until you know it will enough to learn calculus, differential equations and vector analysis. Then you'd be ready to learn basic physics. After that point pick up a text on quantum mechanics and then you'll be able to learn why. Until then you're going to keep making this mistake of thinking that physicists don't understand it. Frankly, physicists such as myself don't really care if you understand it if you're not willing to make the effort to learn what you need to learn in order to understand it.
-
We have not find +1 charge yet. We have +2/3, -1/3 and -1 charges.
How you explain?
-
Haha, apologies for my good well jokes.
Tidal energy source puzzled me. Twice a day, so much energy used to move sea water, if gravity is the source, moon orbit would be changed FASTER.
Tide seems a perpetual movement. Why can't we build a power plant use gravity like the sea does if gravity causes tide?
-
We have not find +1 charge yet. We have +2/3, -1/3 and -1 charges.
How you explain?
You're not making any sense here. You're assuming that particles with certain values of charge have to exist and if they don't then there must be an explanation for it. Nothing about that is true.
First off you didn't mention above that you're talking about elementary particles, i.e. particles with no substructure. But if you really need an elementary particle with charge +1 then you forgot the positron.
Tell me something. Why is it that you expect everyone here to answer your questions but you're not interested in answering our questions. For example: why don't you pick up a college physics text like Haliday and Resnick?
-
Every time a see the word quantum, I want to run, like now.
-
Every time a see the word quantum, I want to run, like now.
That's only because you have chosen not to study it and learn it. Had you chosen learn it the proper way then things would be much different. But you're not willing to do the work. It takes a lot of work, learning a lot of math, long hours of study and years of learning.
-
Hmmm...
So the tides are pushing the moon (7.3 × 1022 kg) away by about 3.8cm a year.
That seems like quite a bit to me.
Say the area of the oceans are about (510,066,000 sq km)
What is the average height of the tides, maybe 2 meters, although perhaps one should think of half of it being raised, and half lowered. Are polar tides less?
So, for moving: 5.1 × 108 km2 x (1m depth) x (1000m/km)2 x 1000 dm3/m3 = 5.1 × 1017 kg of water moved by the tides twice a day.
So, 5.1 × 1017 kg * 365 * 2 = 3.7 × 1020 kg of water raised by about 1m per year.
So...
The moon weighs about 100x the annual tides.
And the orbit is pushed out by about 1/100 the depth of the tides.
There are probably many different ways to do the calculation. Perhaps it would be better to calculate velocity and momentum changes of the moon equivalent to the 3.8 cm change in the orbit. But, my quick estimate for the amount of water in the tides came quite close to the orbital change.
Did you do any calculations to indicate it isn't possible, or did you just conclude that there is a lot of water sloshing around in the oceans?
-
Why can't we build a power plant use gravity like the sea does if gravity causes tide?
We can. http://en.wikipedia.org/wiki/Rance_Tidal_Power_Station
-
You cannot do anything in the UK that impacts on wild life we would rather get our electricity from coal burning plants than have some sand eels or wading birds inconvenienced.
-
You cannot do anything in the UK that impacts on wild life we would rather get our electricity from coal burning plants than have some sand eels or wading birds inconvenienced.
So you decry the notion that biodiversity is important. Is this related to your apparent attraction for false dichotomies?
-
Hmmm...
So the tides are pushing the moon (7.3 × 1022 kg) away by about 3.8cm a year.
That seems like quite a bit to me.
Say the area of the oceans are about (510,066,000 sq km)
What is the average height of the tides, maybe 2 meters, although perhaps one should think of half of it being raised, and half lowered. Are polar tides less?
So, for moving: 5.1 × 108 km2 x (1m depth) x (1000m/km)2 x 1000 dm3/m3 = 5.1 × 1017 kg of water moved by the tides twice a day.
So, 5.1 × 1017 kg * 365 * 2 = 3.7 × 1020 kg of water raised by about 1m per year.
So...
The moon weighs about 100x the annual tides.
And the orbit is pushed out by about 1/100 the depth of the tides.
There are probably many different ways to do the calculation. Perhaps it would be better to calculate velocity and momentum changes of the moon equivalent to the 3.8 cm change in the orbit. But, my quick estimate for the amount of water in the tides came quite close to the orbital change.
Did you do any calculations to indicate it isn't possible, or did you just conclude that there is a lot of water sloshing around in the oceans?
F=ma, V=at. The moon pushed away by tidal force for so long, it should be away way faster by now.
-
F=ma, V=at. The moon pushed away by tidal force for so long, it should be away way faster by now.
F = dp/dt = d(mv)/dt = mdv/dt = ma is correct but you didn't mention what V is supposed to stand for. Assuming its velocity then what is in the velocity of? It's show below that V = at.
Note: The relationship between V and a is a = dV/dt or dV = adt. Let us integrate both sides dV = adt to obtain V = at < c.
-
S=vt, t=5 billion years, how far away should be the moon now? If tidal force came from gravity.
-
S=vt, t=5 billion years, how far away should be the moon now? If tidal force came from gravity.
Your equations are all wrong. That expression only works if the moon isn't orbiting earth and when the earth and moon are modeled as a point particles.
-
In the UK there is an ideal site for a tidal hydro system the estuary of the river Severn and its development has been discussed for at least a hundred years during that time there has been innumerable deaths and loss of habitat due to coal burning that would have been reduced somewhat if this site had been utilised
-
If the moon is receding at about 3.8 cm / year for 4 billion years.
At a constant rate of change, that equals (.038 m * 4,000,000,000 y/1000 m/km) =152,000 km
The moon is currently orbiting at about 384,000 km
Geosynchronous orbit is about 36,000 km, and the moon would have to have formed above that to be in a receding orbit.
The actual calculations would be much more complicated taking into account the difference of gravity over time, the orbital/rotational speed differential between the Earth and moon, velocity, momentum, and perhaps changing depth of the oceans, and even the continental drift and glaciation of Antarctica.
However, a quick ballpark estimate puts the moon about where it is.
-
The a is always there, the v is increasing with t and not constant. Your ballpark is huge.
-
Ignorance is nothing to be ashamed of, unless it is a lifestyle choice.
-
The a is always there, the v is increasing with t and not constant. Your ballpark is huge.
The orbital velocity decreases with time.
Leave it to the physicists to write a program calculating where the moon was every day of its existence.
Suffice it to say that a few cm a year of receding from Earth isn't enough to fling the moon off towards Jupiter, at least not yet.
-
The a is always there, the v is increasing with t and not constant. Your ballpark is huge.
The orbital velocity decreases with time.
Leave it to the physicists to write a program calculating where the moon was every day of its existence.
Suffice it to say that a few cm a year of receding from Earth isn't enough to fling the moon off towards Jupiter, at least not yet.
Let our immortal minds wait and see, story is always getting better. Nature has wonder beyond minds.
-
The a is always there, the v is increasing with t and not constant. Your ballpark is huge.
The orbital velocity decreases with time.
Leave it to the physicists to write a program calculating where the moon was every day of its existence.
Suffice it to say that a few cm a year of receding from Earth isn't enough to fling the moon off towards Jupiter, at least not yet.
No, the Moon's orbital velocity is increasing, not decreasing. The orbital period is increasing. It's somewhat of an oversimplification, but I would say the energy comes mostly from Earth's rotation. We spin about once every 24 hours, while the Moon orbits about once every 27 days--that the tides move are a result of this difference--through the action of the tides (one can think of them as friction) the Earth's rotation is slowing down and the Moon's orbit (velocity) is speeding up.
-
Most of the kinetic energy in the Earth-Moon system is from Earth's rotation, which has measurably slowed ... http://www.lawrencehallofscience.org/pass/passv07/v7SlowingEarthRotation.html
This kinetic energy is the source of the energy in tides.
Theoretically Earth's rotation will slow until there is a double tidal lock (http://en.wikipedia.org/wiki/Tidal_locking) : no more tides, or tidal power, on Earth.
However by that stage the point is moot, as the expanding sun will have boiled Earth dry.
-
Jcc, as I read you you're asking 'what do you mean by saying 'energy'?
And that is a very good question to my mind. You can see it (probably:) several ways. One is the one in where we have a commonly agreed on universe, that we exist in. That one controlled by 'conservation laws', in where 'gravity' is one coin of exchange. The other one is a local definition, well, at least to me.
both definitions though, agree on that when we find something to be true locally experimented (tested) over time and space, we call it a constant.
In the first case what we call a universe is 'energy'. In the second case it's more problematic.
-
or simpler :)
Is a vacuum 'energy', how will you prove it?