Edtharan

Actually it is Global Climate Change, not Global Warming. It was originally called Global Warming decades ago. The reason they called it global warming back then is that they didn't fully understand the processes involved. They knew that certain gasses (CO2, Methane, the greenhouse gasses) trapped heat in the Earth's atmosphere. At the first level, they though that the atmosphere would just heat up (like in a greenhouse), however, what they now realise is that the Heat, does not have to stay as heat, it can go elsewhere. Not only that, they realised that it does not only have to stay in the atmosphere, they realised it can go into the ocean (and not only as heat). But. The name Global Warming stuck because the Mass Media picked it out, and it sounded like a good catch phrase . If it is scientists moving goal posts, then it is moving goal posts not put there by the scientists, but instead by the mass media (and you know how reliable the mass media is for scientific rigour ). Surprisingly this is a possibility from increasing greenhouse gasses. Or at least in certain localities. If the North Atlantic Current is slowed down or stopped by the addition of a lot of fresh water (less dense than sea water) from the melting of the Arctic and Greenland, then this will stop the influx of warm tropical water form the equator (due to the NAC) and plunge Europe into an ice age. If enough of Europe freezes and for long enough, then the reflection of sunlight from the Earth might be enough to cool the Earth, despite the extra greenhouse gasses and drive the temperature further down (and more of the Earth freezes increasing the reflection more in a positive feedback loop) So yes, an Ice Age could be the result of "Warming" the Earth. The climate systems (atmosphere and oceans) are complex non-linear systems. Small changes in a non-linear system can have dramatic and unexpected results. Just because it was called "Global Warming" decades ago by a handful of people and then that catch phrase was then picked up by the media and then they ran with it, does not mean that the "goal posts" that science actually has placed is the same as that thrust upon us by the media.

Global Warming in not simply an increase in temperatures. Actually the name: Global Warming, is a bit of a misnomer (not well named). GW is all about there being more energy trapped within the Earth's Climate Systems (Atmosphere and Oceans). More energy can lead to increases in temperatures (so we will see them), but not all will necessarily go into heating the atmosphere and oceans. Some will go into changing the weather patterns. This means that atmospheric currents will change. Warmer air from the poles might be shifted more north or south warming the higher latitudes. Or you might get air form the poles moving towards the equator which will create a decrease in temperatures in certain locations (not globally, but locally). It might be due to global warming (without more data and a lot of research we can't say for sure) that NZ is experiencing a cold spell (it could also be due to local climatic conditions, but whether these are influenced by GW - and by how much - I can't actually say).

I agree. I think that there will always be the occasional troll that gets through any system, but the tighter you make the system the more legitimate posters will get discouraged. As a personal opinion, I would be willing to let the occasional troll in so that we can better serve those with legitimate purposes.

In a discussion with a few friends (over a few beers ) about this subject, we thought how governments might control population in a way that is not too hard on the population's rights. My suggestion was to introduce a "Baby Credit". This "Credit" entitled a person to have a child and raise it to reproductive age (legally adult or they/partner become pregnant). This credit could be transferred from person to person (hence why it is a credit instead of just a right) so that people who can't or don't want a child can sell their child credits on an open market (so if you want more children you can buy the right to have them). As an example (numbers are just for example and not a suggested value): If each person was entitled to 0.75 Baby Credit (BC), then a couple would have a total of 1.5BCs. They could then have a child leaving them with just 0.5BCs. If they wanted another, they could buy 0.5BCs in the market to raise their total up to 2. However, if they didn't want to have a second child, then they could sell their 0.5BC (or part there of) to couples that wanted more children. Of course, if the child died before they reached reproductive age, they would be refunded their BCs and be entitled for an other (this way if in the unfortunate event that a child dies, the couple is not denied a child or have to go to great expense to regain their right for a child). In the case of a divorce or other split, the remaining BCs of a couple would be shared equally (a default situation) or they could negotiate it as part of the settlement. It is a bit clinical, but the scenario was for a world where population control was a necessity.

This can be explained by better path prediction of Cyclones. Before, they could not predict the path as good as they can now, so they would have to release a general alert whenever a cyclone was in the area. Now they can predict the path far better so that they can be more specific with the alerts. And yes, they do have a cyclone alert system (and it is used), it is just the it is now part of a more general disaster alert system, and because the path prediction is better, they can deploy ground personnel to deal directly with the people instead of just relying on them to be listening to a TV or Radio (which in today's variety of media they can guarantee).

But if that faster runner was in a crowd, they would be effected by those that he runs into. If you were moving faster than light, you would still be effected by the electromagnetic force . Yes, you would leave photons behind, but then you would run into the photons in front of you.

Another way to look at it is what happens to a stationary car that is hit be a wall travelling at 100km/h? /rhetorical question It is the exactly the same as a car travelling at 100km/h and hitting a wall. Or what happens if a car is travelling at 50km/s and is hit by a wall travelling at 50km/s. They are all the same. What you have done here is to not only change reference frames, but change the velocity in all reference frames as well. When we are describing these things, you have to keep track of which frame of reference you are describing it in. In this, you have kept the frame of reference of the wall, and change the velocity of the car compared to that. Lets use 3 frames of reference: The Car, The Wall and a Chase Camera. So, compared to the wall the car is travelling at 100km/h and the Chase Camera is travelling at 90km/h. This is the frame of reference of The Wall Compared to the Car, the wall is travelling at 100km/h and the Chase Camera is travelling at 10km/h. This is the frame of reference of the Car. Compared to the Chase Camera, the Car is moving at 10km/h and the Wall is moving at 90km/h. This is the frame of reference of the Chase Camera. SO, what is the kinetic energy of the Car as compared to the Wall, in the Wall's frame of reference? What is the Kinetic Energy of the Car compared to the Chase Camera's frame of reference?

A wise Jedi once said: "You must unlearn what you have learned." Actually jokes aside, You have grown up and existed in a world where the effects of relativity are so small that we don't notice them. What we call "classical mechanics" (and what you have learned) is actually only an approximation that exist when you don't have extreme environments (like near light speeds and intensely strong gravity). So what you have learned is actually wrong (and that has been proven by experiment). You have to unlearn this incorrect knowledge. First up, you seem to be having a great difficulty with scalars and vectors. I did try to explain, but may be it was not explained from first principles. Remember, forget everything you have learned, or think you have learned about these subjects,as they are likely to be wrong (which is likely why you are having so much trouble with them). First up, Scalars: You are probably familiar with numbers like 1, 2 or 100. These are scalars. They can be of something, like apples. You can have 10 apples. With scalars there is only a single component that describes the number. That is the number itself. Now there are other types of scalar, and they are usually used for a measurement. So you can have 10 degrees Celsius, or 10 metres, or 15 seconds, or 90 degrees of rotation. However, notice that none of these contain a direction. Even that rotation does not have a direction. Is it clockwise, or anticlockwise? Neither, it is not stated and therefore does not have a direction. Now ther eis a type of number that has a direction, and it is called a vector. A vector is made up of at least 2 scalars (see you need to know what a scalar is to understand vectors). An examples of a vector is 20m to the East. In this East is a compass bearing and defined as 90 degrees of rotation clockwise from the direction indicated by a compass as being north and 20m is defined as 20 time the length of the standard (well get to standards in a bit) meter object. Notice that you need both numbers to make sense of the vector. Although people sometimes us the term "Direction" when talking about a compass bearing, this is not strictly correct (for those of a linguistic pedantry nature). The correct term is "Orientation". However, in most conversations, including technical ones, you can get away with the direction because it is understood that if you didn't then give the other part of the vector then you were only talking about the orientation scalar. The reason that we can get away with things like this is because we assume that we are talking to a human that has a mastery of language and can understand the content of a communication despite inconsistencies, short cuts and other techniques. A computer on the other hand can't do this (yet). But this is not a post about communication and computer/human failings. So to summarise, scalars are single numbers that describe a quantity or magnitude. You are familiar with this as in 10 apples describes the quantity of apples. Vectors are made up of two or more numbers (which can be scalars or vectors). One which describes a magnitude (size of the vector) and the other the orientation (direction) of the scalar's value. Let me give an example: Take the vector 20m/s east. Break it up a bit: 20m 1s East There are 3 scalars here. 20m is a scalar of length 1s is a scalar of time East is a scalar compass bearing. Now a vector is a 2 or more scalars. So 20m east give a compass bearing and a distance. This is a vector. It is called a Displacment Vector as it is a vector that indicates the distance and direction that something is displaced. But there is another scalar that is being used: 1 Second. We include this 3rd scalar into the vector and we get 20m east for every second. This is called Velocity. We can also combine the distance (20m) scalar with the time scalar and get 20m/s. Now we get into Dimensions. A dimension is describes as: a direction of measurement perpendicular to all other dimensions. You will be familiar with the first 3: Up/Down, Left/Right and Forwards/Backwards. Up/Down is a single dimension (down is not another dimension, but a direction along the dimension as up is one direction along it). Left/Right is another dimension as it lies perpendicular (at right angles to) Up/Down. You might be familiar with the term 2 dimensional? What this means is that that any point within that space can be described using just 2 numbers (the up/down number and the left/right number). Lastly we have the Forwards/Backwards dimension. This is a dimension as it is perpendicular to both the Up/Down and Left/Right dimensions. You are familiar with 3 dimensional space as this is the space we live in. Any point within 3 Dimensional space can be plotted using a set of 3 numbers. Now, in the descriptions above, I have used familiar directions (up/down, left/right and forwards/backwards), but they don't have to be those exact directions. In fact the directions can change. As an example, what dimension is "Up/Down" for you when on the equator is different for a person at the north pole. Your "Up/Down" could be their "Left/Right", "Forwards/Backwards" or even somewhere in between them. Now onto standards: A standard is a commonly agreed upon object that determines the agreed upon unit. So, a Metre is actually a specific object (kept under very tight security) that all other measuring devices that use the Metre unit must match. A Standard is no way fundamental to the universe at all. It is a human construct, nothing more. However, you can compare one standard with another and work out a conversion factor. This means that we can compare an Inch with a Meter and work out a value that allows us to compare one with the other. But, for this conversion factor to be arrived at, both objects must be in the same frame of reference. That is, they must be stationary with one another and they must also be in the same strength of gravitational field. With the crude methods of measuring that we use and the fact that we don't commonly experience strong relativistic effects, it means that all we really need to do is to place one along side the other to make the comparison. This is where you will have to unlearn things. A standard is not a Chunk of the universe that is somehow separated form it, but it is an object that resides within the universe and is subject to all the laws that govern objects within the universe. This has been proven with clocks. Atomic clocks (the most accurate standard we have for time) will only be out around 0.00000001 of a second each day. They stuck one atomic clock at the bottom of a hill and the other at the top. They left them for a year and compared how far out they were. They were expected to be out by 0.00000365 due only to their error rate, but relativity indicated that they should be out a lot more. What they found was that the clocks were out the exact amount that relativity stated it should. This means that the atomic clocks must have had a different rate of time depending how far up the hill it was. The physics of an atomic clock means it can not be slowed or sped up (if its operating environment is kept stable - as it was). It relies on a specific frequency of microwaves in its operation. These can be checked to make sure that the correct frequency is being used and the atoms them selves can only absorb/radiate that particular frequency in the environment that the clock is put in (temperature). The only conclusion is that time really does run slower if you are closer to a gravitating body than not. This means that a "Standard Second" can only be calibrated when the two "standard objects" are in the same frame of reference. If you change the frame of reference, then that standard is also changed (but only while in that different frame of reference). They have also done this experiment with atomic clocks and planes. they have flown an atomic clock on a plane around the world while leaving another one at the airport. The one that was flying in the plane ran slower, and like the hill experiment, it was what was predicted by relativity. Classical mechanics did not actually predict any change in time. Classical Mechanics stated that the clocks would not loose time. As these experiments showed, classical mechanics is wrong and Relativity is far more accurate. Here is a good bet: If reality is different from what makes sense, place you money on reality.

I agree that in a good debate that semantics are important. I dispute that a computer is not "Natural". Would you consider a termite mound to be Natural. It is the construction of organisms. Most people would consider a termite mound to be natural because it is made be animals. But, they seem to place humans above this. If a human makes an object, it is not seen as natural. Humans are organisms too, they are an animal. So if an animal can make a "natural" construction, then by all rights human constructions should also be considered as natural too. Computers are made by humans, so then if we don't create any special pleading for humans (they are animals not separate from animals), then computers are just as natural as termite mounds (or any other construct made by organisms). It is a kind of reverse Appeal to Nature and a Special Pleading. The special Pleading is that Humans are somehow outside of nature, and then the reverse Appeal to Nature is that we are talking about Natural Selection so because Humans are outside of Nature anything they do with evolutionary algorithms can therefore not be "Natural" (it is a reverse because it is an appeal to "humans aren't part of Nature"). In fact, this is just a reworking of the Elan Vital thinking. Instead of there being "something special about life", it has been turned into "there is something special about humans".

As I have explained (due to you asking this exact same question) in other threads, a negative speed/velocity is a linguistic simplification. Instead of restating all the "relative to" information and calculating the vectors, you can simplify the calculations in certain circumstances (when all the vectors are in line with each other) as a negative value. Only in the circumstances where the vectors line up can such simplifications be applied. So what exactly is a negative velocity? Nothing more than a simplification due the special circumstance that the vectors line up. Do you actually read my posts? Actually you can determine that it is the fan that is turning because rotation is an acceleration reference frame. As an acceleration reference frame is different to a constant motion reference frame, you can always determine hat it is the accelerating reference frame that is moving. The fan blades under go acceleration. In fact, two types of acceleration. The first type is as the fan blades rotate faster. The force that is doing this is called torque and comes from the motor. The second type is due to the fact that it is rotating. All rotational motion, even constant rotation has two vectors associate with it. The first is the tangential velocity, this vector lies at a tangent to the rotation. The second is actually how that tangential vector is changing over time. Remember a vector that is changing over time is actually an acceleration (a vector has a speed and when you divide the vector by a scalar, in this case Time, you get the speed component of the vector divided by time and speed divided by time is acceleration). This acceleration is always at right angles to the tangential vector. This means that the two vectors (one a constant vector, the other an acceleration vector) combine together to specify the rotational motion. As the tangential vector is changed due to the acceleration vector, the acceleration vector must remain at right angles to the tangential vector and so it now points in a different direction.

Well it would show intelligence on the part of the "Bad Boy". If they can get around and out think the "Good Guy", then that shows an ability to understand how someone else thinks, resourcefulness and creativity. All these are traits that are favoured by humans (but not the only ones). Humans are social animals, so if you understand how others think, it gives you an edge in social situations as you cna guess at how others will respond. Resourcefulness show that you can exploit the environment to achive your ends, this might be to "Get some", or it might be to get some food. Resourcefulness is often used as a fitness selection in many different animal species. Creativity is very desired in humans. We praise artists. While making art, you are not actually engaged in the basics of survival. This shows that an artists/creative individual has enough resource to spare that they don't need to constantly seek it out. Such individuals, especially if they are not tied down to a specific locale (like a roving bad boy) send a clear signal that that individual is good at surviving. All these traits are very desirable and so are being selected for in the form of Bad Boy behaviours. The "good guy" who is willing to stick around show that they are capable of holding territory, but not all offspring will be able to get a territory to hold. So if an offspring is capable of working around those that hold territory (the bad boys), then they have a distinct advantage.

You must have skimmed it . And you are right, however I stated that I was only using classical mechanics even though I should be using Relativistic mechanics, but due to the small speeds, the differences would not be too drastic. You did not state this as part of the scenario or as part of the question. Linguistically, the way you have written that scenario and the question, the answer should be 20m/s up the tracks relative to the train, as the question about what speed the ball is relative to the train occurs after the scenario stated that the train was moving 20m/s down the tracks relative to the tracks and the ball was released at 0m/s relative to the tracks. I gave my response to your question and answered quite extensively. From teh thread title and the working of your question (the thread title is something about the future, but the wording of the question has nothing in it about the future), I was uncertain of how they linked together. So I answered the question and also included temporal references so that you could use them better. So if you want an answer that is supposed to be a prediction of the future, then: Once the train has arrived at the station and reached a relative speed of 0m/s relative to the tracks, then if the train or ball does not accelerate in any direction, then the relative speeds between them will remain at 0m/s.

Actually, I disagree. There is nothing in the theory of evolution that states: "Must only occuring in living organisms". Also, there is nothing "special" about life. Life is a series of chemical reactions. There is no "Elan vital" that turns non living matter into living matter. Finally, it is possible to create a biological computer that can perform operations using DNA. You could then program a genetic algorithm into this computer and run the program. This "program" could be for anything, optimising the hull design for a boat, adding fault tolerance into a system etc. The exact same problems that are handled by current genetic algorithms. So, what is needed for Evolution to happen: 1) Reproduction. There must be some way for an entity to copy itself and pass on the information needed to replicate (even if this means hijacking some other process - as a virus does). 2) Variation. Each entity must be able to include variations in its "instruction set" that it passes down when it copies itself. 3) Selection. There must be some way that undesirable solutions can be eliminated and desirable solutions can be retained. How is that different from Evolution? Evolution also works by trail and error too.

Carful... Bad logic there. That is called Cherry Picking. You said to provide you with an object that has layers and is not alive. A frozen lake is exactly what you asked for and now that it has been shown to prove you theory wrong, you reject it. You can't just reject evidence just because it does not agree with your theory. Even if you think the bread loaf is not alive, then this raises further problems for your theory. You have based your theory on the fact that tress and the Earth have some visual similarities (some structures in one look a bit like some structures in the other). But the bread example shows that there are probably more visual similarities between the Earth and a loaf of bread. However, you reject this based on the fact that it does not support your theory. You have rejected both things because they do not agree with your theory. In science, you need to accept that your theory might be wrong and if evidence comes in that disproves your theory, then you either have to reject the theory, or change it to fit the new evidence. What you are doing is not science. And, since this is a science based site, you might want to have another look at your theory and either reject it or change it based on the fact that actual evidence disproves it as it is. Evidence you asked us to provide (and then rejected because it disproved your theory).

I did so earlier, but you seem to have ignored it. Read post #45 again where you asked the exact same question (in post #38) and I gave the answer: "A frozen Lake". So if I build a Hill, does that make the Hill dead? How much of a hill do I need to build to make it dead? Is a single spade full enough, or do I have to build it completely from scratch? But lest look at that loaf of bread. The wheat that went into it was certainly alive. I might have harvested the wheat, ground it up into flour. I then added water and some salt, but while not alive themselves, are certainly found in and used by living organisms. I then added yeast (which is a living organism in its own right). Then I used heat to bake it. Actually, there are even bread products that don't need to be baked (bagels for one), so even that step can be left out. I bet that if I looked hard enough, that I would be able to find a viable living cell in an unbaked bread product (and maybe even in a baked bread product). So, in what way is that bread not alive? If it is just because a human had does something to it, then I ask you: At what level of human interference does something that is alive stop being alive because a human interfered with it? And, then apply that to the Earth. Humans have been digging, damming and generally reshaping most of the surface of the Earth for the last 5,000 or so years. We have radically change the surface of the Earth in that time. How is that different to what we do to the bread?

As we are dealing with velocities far below the speed of light, we can simplify the whole thing by using classical mechanics. This of course only gives an approximation, but this approximation would have an error about the same size (or less) then we would get from the effects of quantum mechanics (uncertainty principle). [/disclaimer] Firstly we must consider vectors. A vector is a composite mathematical entity. That is it is made up of multiple components. A vector has a magnitude which is always expressed as a positive number, and it has a direction. Any object that has a description that includes a direction and the magnitude of that direction can be said to have a vector. It is possible to separate the components of a vector and treat them separately. However, in doing so you have to be careful how you do it and under what circumstances you do. Leaving out a particular component can lead to several errors that, if the full vector is used would produce a different answer. The train is indicated as moving along the tracks in a specific direction. This direction is given as "Down the tracks". So we can use this as a reference. This means that the term "Up the tracks" will be a direction 180 degrees away from the direction "Down the tracks". This Up or Down the tracks does not indicate a speed in any way, only a direction. We could be using compass bearings, but as none was given in the example, we will use these directions instead. The train is also stated (well calculated) as having a specific speed. This is the magnitude of the direction the train is travelling in. So the train can be said to have a vector which we will call its velocity. This defines several important terms: Speed: The magnitude of a velocity vector. Facing: The direction component of the velocity vector. Velocity: A vector that has the components of Speed and Facing. For instance a train that was not moving relative to the tracks could be said to have a speed of 0, and a direction down the tracks. It could also be said under that specific circumstance (a speed of 0) to also have a direction up the tracks, but as the train is indicated as moving down the tracks we can assume that a train will typically be moving in the direction it is facing and so use Down the tracks as the direction that the train is facing in. As common linguistic usage would then indicate, we will us ether default of the direction an object is facing as a common usage for its direction. Thus when referencing a train at rest relative to the tracks we can say that it is moving at 0m/s down the tracks, even though it would be perfectly valid to also state that it was moving at 0m/s up the tracks. This only applies when the train is at rest relative to the tracks, as any movement would give a vector and that vector would then contain the direction of importance. Now at various point within the scenario the train is behaving differently. At some points it is in constant motion relative to the tracks, at others it is accelerating (getting faster or slowing down) and it is also at rest relative to the tracks. This gives us 3 frames of reference with which to examine the relative motions of the ball, train and tracks. 1) Constant velocity: The train is moving at a relative velocity of 20m/s (speed) down the tracks (facing). This frame exists while the train is between the start line and the end line. 2) Acceleration: Although it is safe to assume that the train accelerated prior to crossing the start line, this is not specified as being part of the scenario. So although we could perform calculations for the frames of reference before the train crosses the start line, we are not given any details with which to do so. And, as these frames of reference are placed out side the scenario in question, we can safely ignore them for the sake of this scenario and simplicity. However, we are give details of the train after it crosses the finish line and these are considered as part of the scenario as they are included in the description. Thus this situation counts as another frame of reference. This is a distinct frame of reference that is fundamentally different from a constant velocity frame as objects within an accelerating frame can perform experiments that indicate that their velocity is changing. Such simple ones as a plum-bob (a weight on the end of a string) will indicate a force is acting on the subjects within that frame of reference. 3) Constant Velocity: Finally, the scenario covers the train when it is at rest relative to the tracks. This is a constant velocity frame of reference as the velocity is not changing, even though it is at 0. The scenario states that the train stops changing its velocity when it's speed relative to the tracks reaches 0. As no further information about the behaviour of the train past this point is given, we can therefore assume that the behaviour of any part of the scenario after that point is irrelevant to the scenario and not of interest. It can therefore safely be ignored. Ok, now on to the answers: For the first frame of reference (1), the train is stated to travel a distance of 20 metres of track in 1 second. Using the formula Speed = Distance / Time, we can therefore calculate that the speed of the train is 20m/s relative to the tracks It is also stated that the direction of the train at this point is "Down the tracks". So we can combine this information with the speed to give a velocity of: 20m/s relative to the tracks, down the tracks. An event is stated that at the 100m mark of the track whereby the ball was released with a velocity of 0m/s relative to the tracks. Prior to this event, the ball is assumed to have the same velocity (speed and facing) as the train as no details were given other wise and the ball is stated to be carried by someone on the train. After this event the ball will be considered separate from the train as it is moving differently to the train. At which point we will consider it as its own entity. As stated above, if the ball has a velocity of 0m/s relative to the tracks, then the direction of this vector can be any direction with equal validity. It could even be considered as perpendicular (at right angles) to the tracks and still be equally valid. However, its velocity relative to the train is different. As its speed relative to the train is not 0m/s we must consider its facing component of it vector. As this direction is not given, we have to calculate it. This involves vector addition. We know the velocity (vector) of the ball relative to the track (Speed 0m/s direction any) and the velocity (vector) of the train relative to the track. We can then add the vectors of the train to the track and the track to the ball to calculate the vector of the ball relative to the train. The vector of the train at this point in time (the frame of reference of constant velocity after the ball was released and before the train crosses the finish line) is 20m/s down the track relative to the track. This give the ball a vector of 20m/s up the track relative to the train. Consequently, the train can also be said to have a velocity of 20m/s down the track, relative to the ball. As the ball has a velocity of 0m/s relative to the tracks, then as a check the ball should have the same relative velocity compared to the train as the track does. And as we can see, it does. In the second frame of reference (2), the train is undergoing acceleration. This means that the velocity (a vector) is changing. This change has both a magnitude (the rate of acceleration) and a direction (which direction this change is taking place in). Therefore acceleration is also a vector. However, instead of being a descriptor of a constant velocity, this vector is a descriptor of how the velocity is changing over time. Just like you can have a normal distance divided by time, you can also have a vector divided by time. It is possible to multiply vectors (and therefore divide as well) by a scalar (a number without a direction). This means it is possible to have a velocity divided by time, and since a velocity contains a distance (its magnitude), then this becomes a rate of change, or in other words an acceleration. Distance divided by time is Speed. Speed divided by time is acceleration. A velocity already has a Speed, so dividing it by time divides the Speed by time. In the details of the scenario we are not told the rate at such the train is accelerating, nor are we given the details necessary to compute it. To do so we need to know over what time this acceleration happened (as we already know the velocity of the train, we could use that and the time over which the train accelerated to calculate the rate of acceleration). As we have not been given these details, we can assume that they are irrelevant to the scenario in question. What we can say, however, is that the train was at one point travelling at 20m/s down the tracks relative to the tracks, and at another, later, point it was travelling at 0m/s down the tracks relative to the tracks (using the default direction of the trains facing based on common linguistic convention, not necessarily a mathematical one). This means that its velocity relative to the tracks has decreased. This could be due to one of two things. First, the train might have applied its acceleration direction up the tracks until such time as the relative velocity between the train and the tracks become 0m/s, or that the tracks accelerated down the tracks relative to the first frame of reference until the relative velocities of the the train and the tracks become 0m/s. There are many other descriptions of this event depending on the frame of reference you use. We could have used the ball, the station or even a frame of reference of the train prior to crossing the starting line. However, linguistically, we tend to use the description of the event that is easiest to communicate. In such descriptions, we must always remember, the description is meant to be communicated easily, not necessarily precisely (as this post should attest as I am trying to communicate accurately rather than easily and it is taking a lot more time). Because it is easier linguistically, to use terms such as "decelerate", or "negative velocity", they aren't strictly speaking mathematically correct. Now, as the frame of reference of the train contains a changing velocity and we can't calculate the rate of change in velocity, then we can't actually state what the velocity of the ball is relative to the train. However, as the ball is not the object that is experiencing an acceleration, we can easily give it's velocity relative to another non accelerating frame of reference, say the track for instance. In the scenario the ball is stated to have a velocity of 0m/s relative to the tracks, so therefore we can state that the ball has a relative velocity of 0m/s relative to the tracks. But, as you want a velocity relative to the train, we can't actually easily do this as you have not provided enough information in your scenario description to allow us to do this. Finally, for the third frame of reference (3), the train is at rest relative to the tracks. This means its velocity is 0m/s down the tracks (again, using the linguistic default of the train as explained earlier). We also know that at this point the velocity of the ball relative to the tracks is also 0m/s (with the direction unimportant at this point of the scenario). It is a simple matter of vector addition to arrive at the solution of 0m/s down the track relative to the train. So to answer your question: "What is the ball's velocity relative to the train?" Before the ball is thrown it has a relative velocity of 0m/s down the track relative to the train. After the ball is thrown and before the train passes the finish line, the relative velocity of the ball to the train is 20m/s up the track relative to the train. While the train is slowing down (relative to the track) we don't have enough information needed within the scenario description to give an exact answer to this situation. And, after the train has reached a velocity of 0m/s down the track relative to the track, the ball has a relative velocity to the train of 0m/s down the track relative to the train.

As I keep saying: Just because one thing resembles another, it does not mean that they are the same. You have to provide more than just "they look like each other". I am not talking about scientific lab experiments, just a simple "They share the same processes". Well if we are just only going to focus on the similarities than the Earth is a loaf of bread. Loafs of bread have a crust, so does the Earth, so the Earth is not like a tree, but it is a loaf of bread instead. Also, a loaf of bread can be round and almost spherical, where as a tree log is cylindrical. Therefore the Earth can't be like a log and so must be a piece of bread. Get it. Just because you can point out a couple of superficial similarities, it does not make two things the same. You can point out lots of similarities between almost any two objects. However, that does not make them the same. I can point out many similarities between the Earth and the Ogre, Shrek. Does this mean that the Earth is really a fiction computer generated character? No, of course not. Just because you can point out similarities between a log and the Earth, does not make the Earth the same as a tree log. It does not make the rocks of Earth alive, any more than pointing out the similarities between Shrek and the Earth (both are green and have "layers") means that the Earth is a fictional character in a movie.

If someone is genuinely interested in learning, then their is no such thing as a stupid question.

As I said "potential" points/frames of reference. By potential I mean that there could be a timer attached to them, or you could use a hypothetical timer (not necessarily a stop watch, it could be the decay of a naturally occuring radio isotope in their blood... or what ever). The point of that example of mine was that without a point of reference you can't tell what the velocity is. All movement is calculated relative to some reference point. Giving a compass direction here would be pointless. You know that threw the ball, so that means that the direction is away from me. Again, notice that the reference is relative. If your answer is not 0 you could still be wrong. Yes. Because I didn't explicitly state it, you have to work it out from the context and what is stated explicitly in the example. As the only two things that are stated in the example are me and the ball, then it is implicit that the motion of the ball should be calculated relative to me. As there is no other reference point to compare my movement to, my velocity is indeterminable. To measure motion you need to have a reference point that you can measure the relative motion. If I had included a space ship, and that space ship was not moving relative to me, how fast would I be moving? Well we could say 0m/s because I am not moving compared to the ship. But that doesn't give us an absolute speed so we have to take it further. How fast is that spaceship moving? We can look to the nearest planet to determine the speed of that ship. But that doesn't give us an absolute speed so we have to take it further. How fast is that planet moving? We can look to the nearest star to determine that. But that doesn't give us an absolute speed so we have to take it further. How fast is that star moving? We can look to the nearest galaxy for that. But that doesn't give us an absolute speed so we have to take it further. How fast is that galaxy moving? We can look to the nearest Galaxy Cluster for that. But that doesn't give us an absolute speed so we have to take it further. How fast is that Galaxy cluster moving? We can look to the nearest galactic super cluster for that. But that doesn't give us an absolute speed so we have to take it further. How fast is that Galaxy Cluster moving? We we can compare it to the rest of the Universe for that. But that doesn't give us an absolute speed so we have to take it further. How fast is the universe moving? Hmm we have run out of things to compare my speed to, and we still haven't actually determined what it absolutely is. All we can do is compare it to something else and give a relative speed between them. Acceleration is a Vector. A vector is something that has both a magnitude and a direction. As acceleration is a change in velocity, you not only have to state how much that velocity is changing, but how it is changing (direction). As that description of the change in velocity has both a magnitude (how much it is changing) and in what direction that change is happening in (direction), acceleration must be a vector. But, lets for a second take you view that an acceleration is not in a direction. I am travelling along at 10km/h (fast walking pace). I now Accelerate by 5km/h. How fast am I travelling? Well, if I accelerate in the same direction as I am moving then I will speed up. If it is in the opposite direction then I will slow down. If it is perpendicular to the direction of travel then I don't change speed, but instead change direction (I turn). Opps. Hang on you said that that acceleration is not directional! But all three examples are accelerations, but all three have different directions. The only conclusion is that acceleration must be directional. To understand velocities and accelerations. You might need to learn more about Vectors (Here is the Wikipedia article about them. A good place to start). Yes. Vector Additions. The magnitude is 20 and a direction (in the opposite direction). Vectors can not have a negative value, and velocity and acceleration are vectors, so regardless of the direction, the magnitude of the acceleration or velocity will always be a positive. However as a shortcut (that is you can only do this in special circumstances as it doesn't actually work in all cases, but when you can do it it does make it easier), when you have a vector that is parallel to another vector (that is it either points in the same direction or exactly 180 degrees from the same direction), then you can ignore the direction aspect of the vector and use simple mathematical addition and subtraction. Because we are throwing the ball in the opposite direction we can treat this as a simple mathematical addition/subtraction problem with vectors that point in the exact opposite direction as a negative number. Note that this is not a negative vector, only that in this special circumstance a vector in an opposite direction acts the same as a subtraction in standard mathematics (actually you can do this for vector multiplication and division too but only when you have a one dimensional vector problem - that is the vectors are parallel).

Hi, and thanks. (oh and to help spelling I use the spelling checker that you can get for Firefox, works a treat and comes in several languages too). The problem with this is that the example with the roller-skates throwing the ball is not exactly a closed system. With the roller-skates, they are free to get further and further apart as time goes on. However, if they were connected together by a rope, then when the first skater threw the ball, they would be sent in the opposite direction, but then would then tug on the rope and pull the second skater in that direction too. Then when the ball was caught be the second skater, this would end up stopping the second skater and this would pull on the rope and stop the first skater too. Now if the skaters wanted to return the ball to the firs skater so that they could throw it again, the would be the same as when the first skater threw the ball, only now it is in the opposite direction. The result is that both skaters and ball end up in the exact same place as when they started. A spinning device also follows the conservation of momentum. If I start something spinning (say an electric motor) in a clockwise direction, there is an equal and opposite force pushing the motor housing in the anticlockwise direction. You can actually feel this in those small electric toy car motors. When you turn on the motor you can feel the casing try to spin in the opposite direction. You can break the vectors of rotation up into two separate and linear vectors. One is at a tangent to the direction of rotation. The other is at 90 degrees to this and pointing in the direction of rotation. As this creates a change in the vector, this equates to an acceleration around the shaft of rotation. It is this "acceleration" that give us the "Centripetal Force" that we experience as we rotate (like when going around a corner in a car). When you add the vectors of all these, suing rotation to fling an object away from the motor, it will cause the same equal and opposite reaction to the motor as if you just threw the object by hand. The only way you could use this to get a net movement is to have an open system where you leave something behind (like the balls, or exhaust form a rocket or jet).

Lest go back to linguistics. You know what a Noun is? Well, in these examples each and every noun is a potential reference point. So "Ball" is a reference point, "Train", "Track", "Carriage", "Start Line" and so forth are all reference points. If you only want 1 reference point here is an example: There is a ball, how fast is it moving? Now lets look at this example: There is a ball and I throw it at 10m/s how fast is the ball travelling. Well in this there are two Nouns: The ball and Me. So the movement is implied as being relative to me. Ok, how about this one: There is a ball and I throw it at 10m/s relative to the Earth. How fast am I travelling? If your answer is 0, then you could be wrong. What if I was in a space suit in orbit above the Earth? We can work out what my speed is by using maths. We could find the mass of the ball and find my mass, then apply Newtonian mechanics to work out the forces on me that would allow the ball to be thrown at 10m/s relative to the Earth. So because there were 3 Nouns in that last example, there were 3 potential points of reference (frames of reference). So, in the example that you have been following we have a Train, A Ball, The tracks, The person holding the Ball and the Starting Line. There is not just one point of reference, but at least six! Since motion is relative, it can't be negative. You can express it as a negative, but in reality it is the same as the absolute value. Whether something can be called a negative velocity is only down to the coordinate system (which is arbitrary and does not effect the results). So no. It doesn't go to -20km/h, it instead would go to 20km/h in the opposite direction. Acceleration is not velocity. It is a change in velocity. Therefore if the car brakes and slows down (accelerates in the opposite direction), it is not immediately travelling in the opposite direction as to be travelling in the opposite direction the car would need a velocity in that opposite direction. relative to the road, the car would have it's velocity reduced. Relative to the car following it the first car would have an increased velocity towards it (however, this second car can conclude that because it is not experiencing an acceleration that it is the other car that is changing it's velocity).

It was not that the cells didn't "want" to loose lipids, it is just that cells that lost the lipids didn't reproduce as fast. Because they didn't reproduce as fast, then the cells that had the lipids would reproduce quicker and out compete them. It is just a short hand way of summing up the complexities of what is going on.

I understand what you are talking about. The way that sap oozes form a cut in the bark of a tree does resemble the flow of lava from a volcano. The layers of wood that make up a tree's trunk also resembles the layers that can form with sedimentation. However, I also understand that just because something resembles something else does not make them the same. That is a bit of faulty logic called Equivocation. The processes involved between tree rings and sedimentation layers are completely different. In trees the rings form are cells divide and then die off. In the spring there is more sunlight and so the tree has more energy to grow, more cells can divide and a wide ring is produced. then in Winter when the tree has less sunlight to provide energy form growth (or none at all if the tree is deciduous), then very few cells divide and you get a dense ring. The sedimentation layers you see in the rocks of Earth are caused by dirt and clay particles getting swept up in water. When the water slows down these particles can fall out of the water and settle on the bottom of the river. Over time these build up and as the type of particles swept up changes (due to the river cutting through a different part of the landscape, or a flood, or an ice age, etc) then a different layer gets deposited. Over time these layers get compressed by the layers above them and they harden into rocks. So as you can see, very different processes (one if from division and growth the other from deposition). Because the processes by which they pattern comes about (layers) are very different, you can not just point to one and say that because the patter is similar then they must be the same thing. Tree rings are deposited by a chemical reaction (the growth and metabolism of a tree), where as the sediment was deposited by mechanical forces (erosion and fluid dynamics). This is why Equivocation is not a a good argument. If you were to look at the processes that produced the patterns and the processes were the same, then you would be right in saying that they were the same. So no, even though the layers in a tree look like the layers in the Earth, because the processes that led them to be arranged like that are so completely different, I can't agree with you (except in that they only look like each other).

Here: The post you were talking about was stating that the ball was travelling at 10m/s relative to the people in the train. But you insisted that the ball was really travelling at 30m/s, or was travelling backwards through the train. You are saying that the ball has an absolute speed, but we are saying that there is no absolute speed of that ball. It is perfectly realistic for that ball to be travelling both at 10m/s relative to the people in the train and at the same time be travelling at 30m/s relative to the people on the platform. Which brings me to this: You were claiming that we changed what we were comparing the speed to in the middle of the discussion. However, what you seem to have misunderstood was that we didn't change the speed of the ball, we just looked at the exact same situation from a different frame of reference. Under relativity, this doesn't actually change anything about the situation. Changing the frame of reference, so long as you follow the maths and science, will not change the result of the situation. So changing the reference point like they did was not wrong. Your objection to it however was. Changing the reference point like that does not invalidate the velocity. It only gives a velocity relative to the new frame of reference. What is important is that the new reference frame will be mathematically linked by the theory of relativity to the other reference points. For instance, if we know that a person on the platform is not moving relative to the platform, then any speed a train has moving past that platform will be the same as the relative frame of reference as the platform its self. But, if the person is moving relative to the platform, then we have to apply the translation between the platform and the person to the difference between the platform and the train if we want to compute the difference in reference frames between the train and the person. Also if we know the differences in the reference frame sbetween the train and a second train, we can use that information to compute the difference between the reference frames of the second train and the platform, even if we don't make a direct measurement between the second train and the platform. We can know our mathematics and scientific theories of this situation are correct if we then make a direct measurement between the second train and the platform. Under Newtonian (classical) mechanics this does not give us the correct answer. When discrepancies of this nature were discovered a new theory was put forward: Relativity. Now, when we do these kinds of computations and test them with direct measurements we now get the correct answers! So no matter how much hand waving you do here, you are not going to show that the direct measurements taken do not match what is predicted by relativity. Simply because the calculations have been made,the experiments have been done and they do match. It may fly in the face of common sense, it may not be understandable by you, but the reality is that this is actually what is happening. If something disagrees with reality, then I will put my money on reality.

To start off with you would need temperature differences. If the energy is high in one location (hot) then it will easily move to a location where energy is low (cold). You can then use this movement of energy to do work. However, if there is high energy all around, then it has nowhere to go and so you get no movement of energy and so can't do work. The sunlight itself constitutes a High energy, and the environment constitutes as a low energy. So you could do work by getting it from the sunlight. This would be in the form of solar cells. Another method might be to concentrate the sunlight at a point, thus creating an artificially higher zone of energy (heat) and using the energy from that. If you concentrated enough you could use it to boil water and then pipe that pressurised steam through a steam turbine to generate power.