studiot

Not even for two rotations, let alone 3. You cannot combine vectorially since AB =/= BA, if A and B are rotations. http://demonstrations.wolfram.com/CombiningTwo3DRotations/ You need quaternion or matrix algebra to find the result.

The difference between Swansont's examples and mine are that his examples are of divers or acrobats in free air, with no source of external torque (apart from the initial pus off as they jump). My skater is always in contact with something to push against. This is why again I say to you, " Your scenario is too vague. Please narrow the circumstances down". Edit. Note your aircraft is always pushing against the air.

Don't want much do you? And what on earth do you mean by spinning in the x axis? If they are spinning about the x axis, the x coordinate is the one that will not change.

Swansont has said when it is not possible and I have outlined circumstances when it is possible. What did you not understand?

The common sense that applies to all social media applies here and says Don't post anything you might come to regret or be ashamed of at a later date. The news all too often often reports on the sad fate of someone who ignored this piece of sound advice.

Personally I would call it a causeway. In highway terms a structure is officially a bridge if it spans 1 metre or more.

Where the M5 motorway crosses the peat levels in Somerset it has to cross several rivers. The bearing capacity of the peat is so low that it will not support even the motorway pavement slabs, let alone the bridges themselves. A further complication is that the peat compresses down and subsides, over time, under the weight of the motorway. So the ground levels are always changing. The bridges are founded on very (unusually) deep piles and can be seen to be sticking up or apparantly rising out of the surrounding landscape. The bridges incorporate up to 5 floating run-on run-off pavement slabs to maintain connection between the motorway and the bridges.

We need to work through your questions logically. People are three dimensional and therfore have three rotational degrees of freedom. This means that three simultaneous separate rotations about the three coordinate axes are possible. I do not know of people executing three separate rotations, but skaters have a manoeuvere involving two. When the skater is spinning about a vertical axis, balanced on one leg, the skater leans forwards and pokes her free leg backwards. Then she flips supporting legs by swinging the free leg in a wide arc to land on it. This is then rotation about a second horizontal axis form head to toe through the skater. It is well to enquire how the rotation starts in the first place. This second rotation is started in the same way as the first by bodily swinging a fairly heavy part of the body. A further wrinkle is the possibility of employing the gyroscopic force. This is a force on a spinning object that is also moving along a (straight) line, at right angles to that line. I do not know of any manoeuvere where people reverse the direction of rotation, but the balance wheel in clocks does exactly that, due to the action of its mechanism.

Ok so an 'earth' is not an essential part of an electrical circuit (not all circuits have one), but it is a very, very useful one. The most important property of an earth is that is remains at constant potential and undamaged, no matter how much electricity (current) you draw from it or pour into it. You should note that this is unlike the property of the logitech power supply you asked about in an earlier thread. This had a nominal 16 volts value, but actually varied with the current drawn from it. For the purposes here I will not go into the distinction between potential and voltage and use the term voltage, so Strange is correct in observing that this constant is normally taken as zero. This property of remaining at constant voltage has three principal uses. 1) Since an Earth can accept huge quantities of electricity, devices such as fuses or circuit breakers can be arranged to divert this current to earth to disconnect the circuit in the event of a fault. 2) Electrical noise and interference is basically unwanted variations in electrical potential (voltage). So the constant voltage property can be used to shield or screen a sensitive circuit from the source of this interference. Large currents are not normally ionvolved in this. 3) Again the property of constancy of the voltage can be used as a reference or benchmark for the proper operation of the circuit itself. A final note is that an earth is characterised by a single connectior or one terminal.

I think there was also a question about flowering plants here. If this is the wrong thread I apologise. Try angiosperms http://www.bbc.co.uk/news/science-environment-42656306

When I was younger I used to read a lot of Science Fiction - not all the fantasy stuff you get nowadays but what used to be called hard SF. (funny how the initials converge). Anyway SF used to allow the imagination to explore potential futures and I remember reading a story in the mid 1960s about a very poor girl and her friend a very rich one. The interesting twist here was that in that scenario robots had been developed to such a stage that no-one needed to 'work'. Robotic production units churned out immense quantities of everything. And the poor girl was poor because she was required to consume vast quantities of this production continually. Conversely the rich girl was rich because she only had to eat two meals a day and wear one new set of clothes etc etc. Unfortunately I can't remember the name of the story or the author, though I think it was contemporaneous with Billenium.

Yes I like it too, especially as it encapsulates what I said in my first answer. Another thing about a conductor is that it comes from the word 'to lead'. A conductor provides a path of least resistance and contains or confines the current so that it passes (is lead through) the conductive path rather than an alternative more insulating one.

Actually there are some more basic questions to answer like What does Trevor mean by 'electricty' ? Does he mean AC or DC for instance and does he understand that the answrr could be (and is) different depending. And what characterises 'conductor' or an 'insulator' ? I assume Treveor has some application in mind, which is what I asked about twice now.

Strange was correct. I offered the beginnings of a reply, but you need to understand that the subject is bigger and wider than you give it credit for. I didn't mention arcing. So if you would like to describe as clearly and fully as you can exactly what phenomenon you are thinking of, perhaps we can help you after all.

This is not an easy question to answer. Space itself has a natural impedance of 377 ohms, capacitive. This means that the real part of the impedance (that is the resistive part) is zero. However the conductance is also zero. So whilst free space does not conduct electricity in the same manner as copper wire, it does not obstruct it either. That is how electron beam device such as cathode ray tubes and beam tetrodes work. These can pass very large currents.

Thank you for your honest reply. I was not, in fact, suggesting the need for lots of mathematics in the discussion, though some could help. I think hardly anyone, certainly not the authors themselves, would think of have thought the Copenhagen interpretation to be (wholly) satisfactory. So a good place to start would be to say why it is not satisfactory, rather than to simply contradict it. In particular it does not provide specific answers to certain specific questions about observed reality or experience. (It is difficult to hold a discussion about this subject without using loaded words). My comments on the mathematics refers to my thoughts that it is possible to write down some mathematics that bears no relation to Physics. Physics is also somewhat cavalier in its use of Mathematics relying on results that are actually unfounded in the use of that Mathematics, becuase it ''works' (ie it gets the right or observed answer). This approach has been dubbed the 'shut up and calculate' approach and was prevalent for the last 3/4 of the twentieth century.

What is one of these please? You seem to be offering a circular word argument without any mathematics. Do you not think the fault lies in inadequate (use of) mathematics?

I've not heard that approach before, but i like it. And since I'm always glad to learn new things +1

Yes and this has been answered several times. There is only one acceleration available at each and every point, whether you are an elephant or a mouse. That is the nature of a vector field (acceleration is a vector). Do you prefer mathematics? [math]F \propto \frac{{{M_{earth}}{M_{body}}}}{{{r^2}}}[/math] Since the mass of the Earth is constant, and r is constant at any one point. [math]F = W{M_{body}}[/math] , where W is a constant. Since force = mass x acceleration [math]{M_{body}}*acceleration = W{M_{body}}[/math] or acceleration = w = a constant, independent of mass.

No one is trying to force anything on you and I have already suggested that the numeric line of questioning (as the police say ) is off topic. But please note that Science is not about beliefs. It is about the best conclusions we can draw from all the available evidence. And it is encumbent upon any promoter of a hypothesis or proposal to supply the evidence show how that fits.

Talking of reason, yes a body can have any velocity or acceleration with reason, regardless of its mass. Just as a body can have any volume within reason, regardless of its mass. Yet there are other properties that connect volume and mass or velocity/acceleration and mass viz density and force. So it is true that these connective properties must alter if we select a volume or velocity/acceleration and then change the mass. So what? Swansont has already suggested you concentrate on the object, not the property.

Yeah +1

Only a paltry 10%. Where I live they are currently building what will be the most expensive building ever built anywhere on Earth by a very large margin. It will nearly 20 years to complete. It will produce the most expensive electricity ever produced in the UK, guaranteed by politicians. The design life is 30 years, the decommissioning life is 300 years. Yet it will produce less than 20% of the electricity annually compared to a full alternative hydroelectric scheme at the same location, which would take 1/10 the time to build at less than 1/10th the cost. Additionally the hydro scheme could include a freecauseway instead of a high security zone. Not political? A few years ago I stood in Ballycastle and looked at the finger post towards Scotland, over enough water to power all of Western Europe. Where is the vision?

Hello, Jacky and welcome to ScienceForums. I don't know if this is a homework question or a 'find out project' or something else? Whatever it does not belong in the Modern and Theoretical Physics section either Classical Physics, Engineering or Amateur or Other Sciences or Homework help as appropriate. Whatever what are your thoughts on what is happening to your pan of water?

Would you say the volume of an object depends upon its density or just the linear dimensions of that object? In other words is it necessary to know the density (or mass) of that object in order to completely know its volume? In the same way I can measure the velocity and acceleration of an object, without knowing anything about its mass or any forces impelling it.