vulgarian

I really appreciate your help here but im still struggling. This is raising more questions im afraid! I've knocked up a paint picture to clarify what is in my mind... To me it seems if the dialation is accounted for before the experiment by moving the train sensors so that they line up when at speed. Then when the train tears by, a snapshot from the platform will show an elongated train with sensors lined up, while a snapshot from the train will show a compressed platform with sensors lined up. Ive obviously got the wrong end of the stick somewhere, because following this logic, the observer on the train could just say "Wait a minute! Im am stationary and the platform is moving by me at a great speed, and should therefore appear to be longer, and the observer on the platform could say i am whizzing past a stationary train which should appear to be compressed!" Yeah im taking it for granted that the time that will elapse between the event and observation will differ between the devices on the train and on the platform. Im not sure what you mean by accuracy. Im thinking whatever relativistic effects occur due to the velocity, the sensors on the train will still be balanced and thus agree on the time of the event. (unlike if light is used to detemine simultaneity)

Thanks swansont. I guess what i am getting at is that the relative non-simultaneity of the reference frames seems to me to be a case of perception, much like a supersonic jet passing overhead, and that if light was not used to determine simultaneity then both reference frames would agree on the events occuring at the same time - albeit at different amounts of time ago. So instead of observing the rays of light from each event (which the observational velocity can skew), each event initiates an timing mechanism which can be checked once the train has stopped and isnt travelling at some reality warping velocity! Blimey this is wierd. So if, when the train is stationary, it is the same length as the platform, and A', M', and B' all align with A ,M, and B. But during the experiment it is to be travelling at c/2 when the events strike and the observervers coincide, so before the experiment the distance between the sensors is reduced by lorentz's dialation factor for c/2, then the points wont align at the time of the experiment?

Hi. Im having troubles getting this concept, and it would be really useful if someone can help to clarify my understanding... Referring to Einsteins thought experiment involving the train and two flashes of lightning hitting the track: The reason for these events being simultaneous on the platform, but not on the train, is because the light takes a finite amount of time to reach the observation point. During this time the train has advanced towards one event and away from the other, therefore one flash will hit the observer on the train before the one chasing it. An explanation of this phenomenon introduced the relativistic length of the train, but this does not seem to be important since the extra length with respect to the platform's reference frame should still be balanced and the observation points of the train and platform should still both be midway between the two events when they occur - it seems purely the motion of the train against the finite speed of light that results in the apparent difference of observations. If this is so, how can one say that the event is not simultaneous from the trains reference frame (surely it is just the mechanics of the observational method that makes the events appear to occur at different times). Following from this line of thought another method of conducting the experiment would seem to indicate that the events occur at the same time from both reference frames: At each point where the lightning strikes, a device is placed (one on each end of the platform and one on each end of the train - though the length may have to be decreased on the train to account for the relativistic length due to its velocity). The devices are arranged so that observation points and event points all align spatially when they occur. Inside the device is a waterclock (or decaying atom) that is triggered by the heat of the lightning stike. Checking the progress of the devices on the platform confirms that the events were simultaneous. The two devices on the train should also be equal, even if the ones on the train are less advanced than the ones on the platform due to time dilation, the events were still simultaneous. Sorry if this is a bit long-winded, im just trying to iron out the wrinkles in my understanding of this. Thanks for bearing with me!

Hello, Is it possible to combine the following functions into one? x := 0.5m ft(z) := if(z<=x, f(z), f(x)+f2(z-x)) f(z) := 850*g*z f2(z) := 1024*g*z ft(z) calculates the static pressure at depth z in a 0.5m layer of oil on top of water. So if z is in the oil the result is just f(z), but if in the water layer, f(0.5)+f2(z-x). My fluids lecturer hinted that this kind of problem can be solved without the use of ifs, but didnt seem eager to expand! I'm wondering if it can be solved through knowledge of the pressure-depth gradients of each fluid... but it's mirky!

Im working through an assy about electrowinning copper and done some calcs that im not too happy with. Im not too used to working with amps coulombs, KWh, etc so maybe this is the problem. Any comments on my workings would be most useful cos i gotta get it in, along with a load of other stuff! I need to calculate the energy/power required to electrowin 270 tonnes of copper per day from a sulphuric acid solution. Using faraday's laws of electrolysis: 63.54 * I * 24*3600 = 270,000,000 2 * 96,500 => 270,000,000 * 2 * 96500 = I 63.54 * 24*3600 That makes 9.5 million amps per day! The PD between electrodes is 2V so to find power / energy: (9500000 * 2) / 24 = 791 KWh 791 / 3600 = 219W I think the current calc is correct but sure im getting pickled with the power and energy calculations cos im sure 2 light bulbs do not use enough power to create 270tonnes of copper in a day! another way i worked it is from trial data: 2A for 24 hours yielded 50g of copper. so 270,000,000 / 50 = 5400000 multiplying the 2A by 5400000 gives 10800000A (the diff is because the 9.5MA calc is theoretical) Im just really unsure about how to get from 9.5MA/day at 2V to wattage and KWh per day. help me and i'll shower you with blessings, rescue cats from trees and smile at strangers that pass my way!

I tried to weigh some but got badly burnt!

Please can someone clean up a wikipedia artice relating to the use of white phosphorus. the article that needs attention is here: http://en.wikipedia.org/wiki/Fallujah%2C_The_Hidden_Massacre Basically the documentary includes many images of casualties of the attack on Fallujah, attempting to make a case for crimes against humanity. US originally claimed that WP was only used for smoke screening, later conceding that it was fired into strong holds to 'shake and bake' insurgents. However the documentary claims that WP was used in an indiscriminate manner, being fired from helicopters onto regions of the city, thus constituting crimes against humanity. The film claims that many of the casualties, having horrifically burned flesh but intact clothing, is proof that WP was used indiscriminately. Critics say this is untrue and that the corpses are in an advanced state of decay. One would assume that burning WP would of course burn clothing, but what about the resulting phosphorus pentoxide and phosphoric acid produced by the reaction? Besides being poorly written i feel the following paragraph in the criticisms section could be infactual: The disscussion for the article contains this statement: If anyone here can sort this out or provide accurate scientific information it'd be good!

Thanks only one order of magnitude out though! Ahh but i got it right first time round.

lol thanks nope it's not my strongest point!

Err is this right? mol H2/g = 6.02 X 10e24 Kj/mol H2 = 0.05868 g/L H2@273K = 0.0899 ((6.02 X 10e24) x 0.05868) x 0.0899 = 2.072892124 X 10 to 23 multiplied by our hydrogen production capacity gives 2.7 x 10e34 Kj/hour ???

Oh well, I'll put this one on the back-burner then on second thoughts wiping out all life will do fine. Seriously though, I was more interested in figuring out the explosive power of our electrical consumption. I found getting my head around moles a bit vexing when at school. Though 1 gramme of hydrogen contains 6.02 x 10 to 23 atoms and Heat of fusion for hydrogen is 0.05868kJ/mol. So how many grammes of hydrogen are in a litre at atmospheric pressure?

If 1000w is enough power to generate 170 litres/hour of hydrogen from saline water and the UK has a power production capacity of 77.4GW how quickly could we blow the world up? Sure it would be a lot easier to release our arsenal of warheads but thats boring. I reckon if we put the wires in the channel near france, within the hour we'd have something like 131 580 000 000 litres of hydrogen to play with. How much explosive power is this? Standby buttons alone probably account for enough to wipe out london.