studiot

Well I was referring to the connection between straight lines and geodesics in Newton's First Law. I don't know if Galileo ever referred to the important concept of The Right Line

For static charges or steady current, the statements:- The E field is conservative, has a scalar potential, V (as introduced by imatfaal), has a zero curl, has a line integral around any closed curve equal to zero, are all equivalent statements that are proved by simpler means before Maxwell is introduced. Since these are all mathematically equivalent only one is chosen as the basic and the others follow mathematically. One of the difficulties in replying to this is avoiding a circular argument. So where does your course start? Also where do you stand on vector algebra and vector calculus in 3 dimensions?

Was this a quote from Euclid or Newton Or..............?

I expect that was a simplification imposed by your teacher. What did she have to say about Helium and Avogadro's Hypothesis? Historically the concept of atoms was introduced followed by the concept of elements and finally the concept of compounds. Three laws were enunciated The law of Definite Proportions The Law of Constant Composition The Law of Multiple Proportions These codified the idea of 'pure substances' that could be formed from or reduced to simpler forms of matter (called elements), which could not be reduced further. The natural question arose "If an atom is the basic form of an element, what is the basic form of a pure substance?" This lead to the idea of a molecule, after quite a few false trails and some obstruction by some older scientists, lead by Berzelius. The concept of a bottle or bag of a pure substance containing multiple instances of identical units is simple and alluring and offers a working explanation for many physical observation. But it is only a model and not always reliable. For instance what does a molecule of pure diamond look like? If you are still reading this rather than moving on I was going to discuss your view of the space between atoms with some hopefully helpful comments. Are you still interested?

I'm sorry I didn't make myself clear. I was not asking how the temperature changes were deduced. Your vertical axis plots change of temperature. Change from what temperature? Is the change from a common base, an average or some function of the previous temperatures? Also what about the particulate counts?

The fraction by weight of a particular constituent in a given precipitate. For example the chemical factor for Fe in Fe2O3 is 0.6994. So if we have a precipitate of 10g of ferric oxide it contains 10 x 0.6994 g of iron Good gravimetric analysis texts offer tables of chemical factors. You can also use stochiometry of the reaction to calculate the fraction yourself, if you do not know the factor. Can you work out how to do this?

I'd be interested to learn more about those graphs. Pavel. What does the temperature variation [math]\Delta T[/math] vary from? And what is is the variation in temperature of? The carbon dioxide levels are self explanatory. The dust levels are stated as ppm dust levels in what, thae atmosphere, the ocean? And ppm measured how? The correlations are interesting, however, and hopefully less distorted than the Gore efforts. Many thanks.

So did I, isn't it?

Not to contradict ajb, but to add: It should be noted that the value of something may or may not be equal to its limit, if it only has one limit.

Although I realise you are interested in testing out Maxwell, you don't need Maxwell and vector calculus to solve this one. Indeed having a physics feel for what is going on is important. With a steady direct current, the electric field situation is the same as a line of charges, viz the charge/current density never changes and the field has radial symmetry. The E (and D) field lines must be at right angles to the B (and H) field lines. As you rightly observe the B field lines form concentric circles around the line of the conductor. How would another set of concentric circles be orthogonal to these? You asked where the flaw in your reasoning lies and I pointed to the step from 3 to 4. In step 3 you correctly say that if the E field is circular then curl E is non zero.. The error is in chosing the circular diagram, not the star in the top left of your attachment. The electric field cannot form closed loops. It starts or ends on a charge or goes to infinity. The magnetic field, however cannot have ends. It can only form closed loops. You can also apply Maxwell to show the consistency of this.

Ever the too practical Scot.

Edit sorry I missed a minus sign [math]\nabla {\bf{.J}} = - \frac{{\partial \rho }}{{\partial t}}[/math]

Where have you accounted for continuity in step3 to step 4? [math]\nabla {\bf{.J}} = \frac{{\partial \rho }}{{\partial t}}[/math] Note continuity is not one of Maxwell's equations. In free space you also have the conduction current J = 0

At least show that you can correctly add two forces.

Ah magic, I should have known it was not real science. Sorry I am in the wrong forum.

Vacuum cored Tx?

Sensei and strange, sounds like you two are quibbling. This is meant to be basic and elementary to present concepts and promote understanding. What exactly did you not understand?

yahya, Did you miss post#4 or are only certain members allowed to comment?

Tylers, This is all getting very complicated. One simple distinction you should know is the difference between atoms and molecules. All atoms are molecules. But not all molecules are atoms. Molecules are the smallest unit of any substance (ie matter). The definition of any pure substance is that all the molecules are the same. Some molecules can be broken down further but the results are not the original substance but atoms. Atoms are molecules of special substances, known as elements. These cannot still be broken down further and remain as matter. All molecules are made of slightly less than 150 known elements. Some elements exist in normal conditions as multiple atoms of the same element forming molecules. Examples are oxygen and hydrogen. A combination of oxygen and hydrogen exists as the water molecule. Helium normally exists molecules comprising a single atom. Hope this helps.

I think you misunderstand the nature of centripetal force. Centripetal force is a real force that has to be applied to a body travelling in a curve, by an external agent, if we can consider that body to be a point particle. Gravity is one such external agent and the gravitational force is centripetal in nature. A point particle means that all the mass of the body can be considered to act as though it was concentrated at one point. Centripetal forces act within a body turning on an axis, but not on the body as a whole. These forces act between the individual particle or parts of the body and are usually manifest as a variation in the cohesive forces holding the body together. There is a further complication in that the centripetal force at any point in the trajectory (which may not be a circle), is directed towards the centre of a circle, which has a common tangent to the trajectory curve at the point of interest. In general, when the trajectory is not a circle, this centre point will vary in position and the distance between the common tangent point and the centre (known as the radius of curvature) will vary. In order to account for this it is usual to work in terms of acceleration, not force, and call this centre the 'instantaneous centre of acceleration'. Working in this way you can add the accelerations (vectorially) on any part of an orbiting planet to generate the true path of that particle on the planet. The accelerations are, as you say, separately due to the centripetal effect of gravity acting on the planet as a whole combined with the internal accelerations due to spin, wobble and other movements, including variation of linear speed. Very tricky indeed.

+1 for fairness and astuteness. With all due respect I would see this as a political statement rather than a scientific one.

I like levity +1, sunshaker.

How about this famous one http://en.wikipedia.org/wiki/Growth_in_a_Time_of_Debt

+1 Never seen one of these, thanks.

Again I am currently short of time but you are missing part of the equation [math]{\bf{B}} = {\mu _0}{\bf{H}} + {\mu _0}{\bf{M}} = {\mu _0}\left( {1 + \frac{M}{H}} \right){\bf{H}} = {\mu _0}\left( {1 + {\chi _m}} \right){\bf{H}}[/math] Look up susceptibility.