studiot

Interesting question. Say you take a surveyor's measuring wheel and trundle it along the road, recording the distance. Are you doing 'maths' ? ie utilising the inherent properties of a circle to obtain your result ? I would say yes.

First we divide the universe into two parts. The system and the rest of the universe. The rest of the universe is usually called the surroundings or the environment. Dividing the two we have the system boundary. For instance you might choose the walls of the fuel barrel as your system boundary, the contents of the barrel as the system. Work is done when the system boundary is displaced. If the system expands the system does work on the rest of the universe. If the system contracts the rest of the universe does work on the system. This is one form of energy flow across the system boundary. Heat input (or output) is another Electrical energy is another and so on. Any system already contains energy stored up in chemical bonds, pressure, and so on. This pre-existing store is called internal energy and changes often result in changes to the internal energy. The internal energy is balance sheet of all forms of energy already within the system. Any new energy added to the system as a result of the system process adds to the internal energy in some way. Any energy output by the system is subtracted from the internal energy. This leads to the First Law or law of conservation of energy. Change in internal energy = Work done on the system plus heat added plus other energy added This change can be positive or negative, negative indicating that energy leaves the system. In your case, initially the combustion energy of the match is input to the system, slightly increasing its internal energy. The resultant explosion releases chemical bond energy as kinetic energy (pressure) of the combustion gasses which rapidly leave the system in the explosion. Does this help?

plus1

Humblemunn, are you sure you are not confusing simulation based on probability/statistics rather than closed form mathematics with non mathematical activity? For example queueing theory, mass behavioural science etc.

mad indeed. Take a rod, tube, pipe or other object of circular cross section. Tell me how to measure its radius? The practical world out there works in diameters because that is what a pair of calipers measures.

Not quite sure what you mean by this. There are many factors in play. Here are some more proceedures from my experience. Given some pieces of steel plate how would you generate a genuine flat surface to any desired degree of accuracy? Given a brick, fresh from a kiln, it takes up moisture and expands slightly over time. This can lead to enormous forces if that brick is restrained as part of a wall. How would you monitor this expansion over time, given that the necessary measurements are of the order of 1/10,000 of an inch? Applied scientists (and researchers) face this sort of issue every day.

I didn't ask for stress calculations of any description, as they have nothing to do with how much water you need to add to the mix. Yes but that will not give the correct answer, so perforce it is not a correct analysis or model. That is why no-one in the whole world attempts to just add a specific amount of water when mixing structural concrete (or even fence post concrete). What is actually done is a smaller amount of water than calculated by your method is added and then the final amount is 'trimmed' to suit after making workability measurements and then adding some more water. This extra water will be different if every case. Hence the instruction "add water until it is correct" If you would like to know more I will happily tell you, but don't get on your high horse about a subject you are not expert in.

So what was your answer to my question If it is possible to specify an exact amount of water to achieve a desired workability, what is the formula?

Thank you for the link. Yes your source offers a specific amount of water. I note he even uses zone2 sand. Have you ever tried this proposed method? Let us suppose you are on site and your concrete is arriving in 6 cu metre mixer lorries. You are in charge so you give the instruction to add exactly 1203 kg of water to each lorry. Now you are pumping this concrete into a large pour and the pump company says they will not pump concrete that has a workability of less than 65mm slump, whilst the resident engineer will reject all concrete that has a workability greater than 75mm slump. Concrete is £80 per cubic metre so each lorryload discarded costs your company £480. Your boss says that any discard will come out of your wages. How much will you loose? PS I have been in this situation on a large bridge deck pour and lost nothing after pouring over 1000 cu metres. But I did not add water your way, or by any mathematical formula. Oh and by the way, all that stuff on plasticity has almost nothing to do with reinforced concrete engineering, even using the plastic design methods available in the codes.

Go on then, post a formulae that will unequivocably determine the amount of water in 6MPa concrete, made with 20mm BS graded aggegtate, and zone2 sand. No additives, or pozzolans are allowed, cement to be OPC.Temperature on site +15 degrees C.

Absolutely not. That is the whole point. The instruction is "add water until the consistency is correct" This amount of water is not set and is different in every mix of concrete (allowing for total quantities)

Humblemum Simulation is generally about process. But underlying both simulation and other forms of modelling is the assumption that the model follows a sufficiently similar set of rules to that being modelled for the product of the processes to be put into correspondence in both systems. In post#141 I posted a process that I maintain cannot be modelled by mathematical formulae alone. I challenged the mathematicians here to offer such formulae if they disagreed. I now challenge you to post a method of simulation for the process of mixing concrete to the desired consistency.

If you wish to create a new system of thermodynamics based on your own private definitions, you will find it very hard in this world. Better to learn and use the established ones.

Well I assume you have the equation for the efficiency, which does indeed show that [math]e = 1 - \frac{1}{{{r^{y - 1}}}}[/math] Since the compression ration, r is greater than 1. In the derivation of this equation use is made of the fact that the compressions are isentropic (adiabatic) so that the expressions [math]\frac{{{T_2}}}{{{T_1}}} = \frac{{{T_3}}}{{{T_4}}} = {r^{y - 1}}[/math] hold good. These are used along with the basic definition for efficiency (output/input) to derive the above expression. So the short answer to your question is becasue the two compressions are isentropic (adiabatic).

Before you can identify your input energy, you must specify your system, system boundary and system process. Input energy is defined as energy that crosses the system boundary during the system process. So if your system is the barrel of fuel, than no, the chemical energy stored in the fuel is not input energy it is internal energy.

Did you read the referenced article? If so how do you reconcile the solution to the differential equation (where the exponential comes in) with your theory?

This is a claim but I see no maths to substantiate it. This seems a fairly easy to follow derivation of radioactivity probability. http://www.csupomona.edu/~pbsiegel/bio431/texnotes/chapter2.pdf

Entropy is the ratio of the quantity of heat transferred across a system boundary to the temperature of transfer.

But what does that have to do with entropy? And focused light still travels at the speed of light.

If it's not a stupid question, how would you move the magnet once you had attached it to the vehicle? Could you not use whatever to pull the car directly?

Defy entropy ? What on earth do you mean? Perhaps you could put some numbers or at least equations to it?

Sometimes we don't want to reduce the eddy currents. Look up the 'eddy brake' or 'eddy brake disk'. Knowing what enhances the effect can point towards reducing it.

If you are talking about algebraic identities Consider the two equations 3x2+8x+6 = 2x2+5x+4 3x2+8x+6 = (x2+4x+1) + (2x2+4x+5) The first is only true for certain values of x - This is an equation. The second is true whatever the value of x - This is an identity. So you need to show that the condition is true for all x.

I do not have access to this book now, but try here Charles Taylor : Ancient and Modern Geometry of Conics (Cambridge 1881) contains much history of the subject. The original book was by John Wallis in about 1661

As I said I was not available over the bank holiday but can carry on now. The problem with air bubbles is that they presumabably lead to a homogenous material. Entrained bubbles will also lower the susceptibility in the flux direction. The point I have been trying to emphasise is that the eddy currents act in a particular direction, so you only want to change the properties in that direction. I also noted that eddy currents are circulatory in nature. The reverse emf they generate depends upon the area of the circle. Again entrained bubbles would not reduce that area in the way that complete separation by lamination provides. Finally in any material where the emf is induced by motion in a steady field, rather than a changing field, the emf is induced in all the moving material immersed in the field. You need some part of the material that is not immersed in the field for the return half of the circulatory current to flow.