studiot

No, just don't go there. Having got that out of the way your other two questions are entirely reasonable, but very difficult to pin down. As already noted by others, energy is a property, but you might reasonably ask a property of what? Well energy is a property possessed by a system by virtue of its configuration. Generally there is an energy change associated with a change to that configuration. We observe this in many ways A ball rolls off a table and falls to the floor A kettle of water boils to produce steam A fast radiation particle precipitates a droplet trail in a cloud chamber Sodium carbonate and calcium chloride solutions precipitate calcium carbonate solid particles when they are mixed. The thickness of the brake pads in your car (I hope they are finer than 36 grit) decreases with use. It is also said to be the capacity of a system to perform work. This is the definition where energy is usually first introduced in elementary Physics. But then we go on to talk of available and unavailable energy (Clausius and Maxwell) in more advanced work and then zero point energy (Plank) in even more advanced work. This shows that not all energy can be used to perform work, even in theory. So where are we? Well the answer raises more questions than it answers. And we have yet to define a system, or configuration. I can't say the exact number, partly because there are so many and partly because there is some overlap in usage. Expressions for energy appear in pretty well all branches of physical science, each one tailored for use in its particular area. A great deal of work over several centuries has taken place to make sure that they are all consistent today.

A small observation (not a criticism). All the choices so far presented seem to be of the 'all or nothing variety' for instance Perhaps you were actually taking your girlfriend for a Chinese meal and the choice was not jacket or no jacket but jacket or chinese because you had money in your pocket / on your credit card for one and not the other. I chose to go to Scotland on my last holiday, not Tibet. In this case I was spending time, not money as holiday time is limited, though I could have afforded the money for both.

Firstly you have written Rth as 8k in red, which is 10 times too much. Edit I see you have .8 k sorry - a piece of advice never omit the leading zero before the decimal point. Rth = 0.8k Secondly they say (correctly) exactly how the thevenin voltage is calculated in their text. Remove the load (20k in this case) Use simpler circuit laws, eg potential divider (in this case), KCL, KVL etc on what is left of the circuit to determine the open circuit voltage between the terminals of interest (A, B in this case). Just follow that proceedure on a couple of examples to get the hang of it. It seems a bit silly on such a simple example, try it on a more complicated one.

This is good https://www.amazon.co.uk/Chemistry-Palgrave-Foundations-Rob-Lewis/dp/0230291821 and this is good https://www.amazon.co.uk/General-Chemistry-Principles-Modern-Applications/dp/0132064529 After these you will need to look for books in specific chemistry subject areas eg organic chemistry, analytical chemistry etc. One more for the road for those who are cramming for an exam bu reading for love of the subject. https://www.amazon.co.uk/Atkins-Molecules-Peter/dp/0521535360

CPC-farnell are a regular supplier of mine, but I didn't know what wattage you needed. I suggest you look at industrial ceramic heaters in Screwfix or MachineMart. Just no-nonsense power. However I claim my share of the chestnuts.

http://cpc.farnell.com/clarke-international/6920262/devil-350-2-4kw-ceramic-heater/dp/HG00946?ost=ceramic+heaters&searchView=table&iscrfnonsku=false&ddkey=http%3Aen-CPC%2FCPC_United_Kingdom%2Fsearch You mean like this?

I was born in England and consequently my first language is English. As such I am quite accustomed to words have several meanings and people restricting these meanings to a particular one or part of one for the purposes of discussion. I am also accustomed to this in the narrower ambit of scientific and technical English, where it is even more common to prevent misinterpretation. So for instance I might start a lecture by defining a differential as a particular system of gearing one finds in many vehicles. Others might use quite a different definition. Scienceforums is similarly entitled under both the usage practice of common and technical English to make such a restriction, quite apart from the modern belief that business can mangle our once great language as it pleases.

This is a fair question that does not seem to have been answered. It is called kissing contact.

I really don't understand what you mean by this, but I hope you have not taken offence. Certainly none was intended so I apologise if you felt offended in any way. I was hoping to cheer people up in this thread - perhaps I would be better keeping out of religion, I usually do. Meanwhile you don't seem to be visiting the post I drew up especially for you in your electrical engineering thread.

Galveston is a long way to go for Sunday worship, I'd probably be late.

Gosh what a jumbled up question. Is this homework or a test that you require such an urgent answer you have to leave before anyone can answer? It certainly does not belong in modern and theoretical physics. OK so release of energy when you walk, and presumably when travel by the other means stated as well. Released is not really the correct term but we can discuss this if you ever return. Conservation of energy requires that energy is generated somewhere during the activity and transferred to the support surface, by work being done on the support surface (mechanical energy transfer) or by temperature difference between the traveller and the support surface (heat energy transfer). Friction will only do work if there is slippage or sideways movement between the contact surfaces. Work is done in deforming both contact surfaces and transferred to the support surface as strain energy. You have not offered the examples of cutting or grinding tools, but work will also be done in cleaving the support material. Finally, as delta1212 observes, impact work will be done if there is impact rather than smooth rolling. Momentum is not work or energy.

Again short and to the point Mordred. +1

I'm still waiting for an explanation of what forces are involved in boiling a kettle (my post#3) A further question to consider. Why is there no matter or mass whatsoever included in the electrostatic force equation. This equation will function equally well in a universe without any matter since charge itself has no mass.

The effective mass of holes in conductors is generally positive. It is electron behaviour that can require negative effective mass to explain classically.

Especially for Catholics.

Forgive me but was that meant to be a reply to my question. If so I really don't understand so please explain in greater detail.

Not only did I spot it, I liked the way you avoided juxtaposition of self contradictory terms. However this one baffles me Ionise a vacuum? My latest guess is that you want to construct a source of ionized air for test purposes in your goal of recovering energy from already ionised air. I don't know where you are or what your resources are but these guys are really friendly and swop useful kit a lot. http://www.vintage-radio.net/forum/index.php

What happens when you boil a kettle? What force generates the steam as opposed to adding the latent heat causing it?

So here is the first session of a couple or three session crash course in calculusy things. Many authorities advocate teaching integration first and that is probability appropriate here. So what is integration? Well integration is a way of adding things up – it is a sum. Indeed the [math]\int [/math] symbol is the Gothic letter, for the Greek letter[math]\sum [/math] , we use for summation. But it is much more than just summation; it involves adding up lots of products that are the result of multiplying two quantities together. This is very very useful to us in the real world because we often want to do just this. Just to list a few instances. Area = height x Length Distance = velocity x time Heat supplied = specific heat x temperature change Potential Energy = Height x acceleration due to gravity Electrical power = current x voltage Metered electrical energy used = power x time And many many more besides. Integration is often introduced as ‘the area under a graph’ and indeed Area is the first on my list. But integration can provide a great deal more since calculating the left hand side of each equation involves some sort of integration of the right hand side. Important points about my list The enormous number and variety of quantities encompassed. Some of the quantities are variables, some are constants. Some of the multiplied quantities have the same units, some have very different ones. A consequence of (1) is that when we come to write things out as mathematical expressions we have a symbols problem. Because we have only a few symbols to work with, mostly Roman and Greek letters, some must do double (or more) duty. Care must then be taken to avoid confusion different quantities represented by the same symbol as happened in your opening post with watts (power) and work (energy). Further it is sometime difficult to choose which common quantity to represent by the first letter for example voltage or velocity, distance or diameter, etc. Now let us look at the format of an integral [math]\int\limits_{x = a}^{x = b} {\left( {{\rm{expression}}} \right)} dx[/math] We see the product of two quantities, (expression) and dx to the right of the integral sign and two statements about different values of the variable x associated with the integral sign itself. This brings us to point (2) above some quantities are variables and some are constants. We choose one of the variables as the base variable for the integral. This is called the running variable or the independent variable or in some cases a parameter. The dx part is always in terms of the running variable - x in this instance. The point is that the integral covers a range of values of this variable, not just one as is the case with a constant. So we can’t use a constant as the base. The range of values taken on by the running variable is starting at the value at the bottom of the integral (x = a ) and extending to the value at the top (x = b) and covering all values in between. In order of difficulty the (expression) can be A constant An expression in the running variable – x in this instance An expression in another variable. So what to do with this integral? If we take the black box from my post#10 and define the process inside the box as “Look up the integral for (expression) in a table of standard integrals and then write the result within square brackets we have” [math]\int\limits_{x = a}^{x = b} {\left( {{\rm{expression}}} \right)} dx = \left[ {{\rm{Integral}}\;{\rm{from}}\;{\rm{tables}}} \right] = \left[ {{\rm{new}}\;{\rm{expression}}} \right]_{x = a}^{x = b}[/math] Then we write the beginning and end values of the running variable at the end of the square brackets. I have used the full version x=a, x=b to make it clearer, but the x= part is often dropped. However keeping the x= is not onerous and helps when we come to part 3 on the list and change of variables, which you had trouble with. We evaluate this by putting the values of x at b and a into the new expression and subtracting thus. [value of new expression at x=b] - [value of new expression at x=a] (Note which is subtracted from which) To see how this works let us look at the simplest possible examples. If (expression) = 1 (that’s right one) And a = 0 and b = 1 we have [math]\int\limits_{x = 0}^{x = 1} 1 dx = \left[ {{\rm{Integral}}\;{\rm{from}}\;{\rm{tables}}} \right] = \left[ {{\rm{new}}\;{\rm{expression}}} \right]_{x = 0}^{x = 1}[/math] If we look up the integral of 1dx in tables we find it is x so putting this in we have [math]\int\limits_{x = 0}^{x = 1} 1 dx = \left[ {{\rm{Integral}}\;{\rm{from}}\;{\rm{tables}}} \right] = \left[ {\rm{x}} \right]_{x = 0}^{x = 1} = \left( {\left[ {x = 1} \right] - \left[ {x = 0} \right]} \right) = \left[ 1 \right] - \left[ 0 \right] = 1[/math] We now have something we can start applying to your original post, so I will stop there and post this and await feedback.

Very quickly (there could be more, I have a good deal spread about.) is this the sort of thing you are looking for? https://books.google.co.uk/books?id=DSHSqWQXm3oC&pg=PA936&lpg=PA936&dq=pulse+terminology&source=bl&ots=o0QQEMJH9R&sig=QPagCDwrh4-bV2zeC5SGczqngf0&hl=en&sa=X&ved=0ahUKEwjunfbq7svTAhWpLsAKHfLCChM4ChDoAQgUMAA#v=onepage&q=pulse%20terminology&f=false

Don't worry it will all become clear as I work through it. But it will take a little time to write out all the maths. So I have posted this since I see you are online right now.

Hi Ed, I don't disagree with what you are saying. But it is not the vertical axis that is the problem it is the horizontal one. Any self respecting pulse generator has a DC offset controll that will move the generated pulse train up and down on the vertical axis. Any receiving circuitry can alter this to suit, with simple blocking capacitors / DC restorers at will. None of this will affect the basic nature of the pulse train. However the generator will have not one but two oscillators to generate the pulses if it has variable mark/space ratio. This is because there are inherently two independent frequencies in play in pulse generation. Each frequency is needed to define the two halves or aprts of the pulse train. If the pulses are of very short duration ( very small mark/space ratio) then that part of the pulse will need much higher frequency circuitry to handle it. You didn't answer my question in post#21? Did you look up magnetohydrodynamics, the techniques there seem ideaaly suited for your needs. You should also look up the work of Nobel prize winner Alven https://en.wikipedia.org/wiki/Alfv%C3%A9n_wave

Hi mondie, it is kinda difficult for me to know how to help wihtout at least some reaction to my last post. My next step wouold be to work through your posted example maths, line by line. But I don't know if you are interested in the maths or the electrical engineering?

Hi Ed, yes there are several viewpoints and I know that many (including Wiki) use the term pulse frequency without much thought. The problem is Consider a pulse, 10 nanoseconds long, repeated every 10 microseconds. What are you using to define the frequency the 10 nanoseconds or the 10 microseconds? Do you think a circuit with a bandwidth of 100khz would pass this pulse train? The term frequency can be used with some meaning for a square wave and you could expect a square wave with an 'on' time of 5 microseconds and an off time of 5 microseconds to pass such a circuit with some rounding but a still appearing as a recognisable square wave. Very short pulses need additional information to describe them properly, which is why radar engineers invented PRF and all the other terms. Your interposing cloud of electrons would appear to me to constitute a plane rather than a pulse?

The math huh http://mathworld.wolfram.com/DeltaFunction.html There are some pretty pictures of a sine expansion, amongst others. But see also my response to Strange below. I particularly liked your last sentence, emboldened, especially the bit about pulsed DC, which is what I was talking about and Handy would be generating. What exactly is the non zero portion of a perfect pulse if not DC? It is a stright line parallel to the horizontal axis. Because of this when designing say pulse transformers or transmission lines etc it is common to break the puls into three sections. Section 1 The rising front is analysed by high frequency equations since it has many high frequency components, Section2 The flat top is analysed by DC or low frequency analysis since it ideally has zero freqency components Section 3 The trailing edge is analysed by HF analysis as the leading edge. An additional pulse characteristic called droop is introduced in real world analysis of section 2. This sort of situation appears in radar systems, and in analog power supplies where enormous current pulses occur for very short durations during the reservoir charging/discharge cycle. See here particularly the quote underlined. http://www.thefouriertransform.com/pairs/impulse.php Frequency = 1/wavelength yes? So what is the frequency of a zero length pulse? So I am saying that both terms are inappropriate for some repetitive and non repetitive 'generalised' functions. We see these in solitons, heaviside impulse functions and dirac functions amongst others.