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studiot

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Everything posted by studiot

  1. The net force causing the acceleration is Force = mass x acceleration. In the dynamics of motion we regard gravity as an acceleration (g), not a force, so Weight is the name we give to the force that gravity exterts on a body of mass m. W = mg In this system, remember that kg are units of mass, not force or weight. Force is in Newtons. (you have to convert if it is given in any other units) So W is in Newtons, mass is in kg and acceleration is in metres per second2 Does this help?
  2. You are right to say there is more than one way to skin a cat, or more than one way to discuss this. However please be careful not to mix up ideas from different ways. The classic second law of Kelvin and Clausius refers to cyclic processes. This is not a cyclic process. You rightly mention that Chemists introduced the Gibbs Free Energy and chemistry/chemical engineering topics are normally discussed from this viewpoint. The free energy approach incorporates all forms of energy, heat, work, the entropy-temperature integral etc. Order is not expressly distinguished, it is included in the calculations. If you wish to discuss in statistcal mechanics terms (order and disorder) Caratheodory's formulation is better. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics It is easy to state (it is obvious) that a crystal lattice is more 'ordered' than the solute phase. Unfortunately most people misunderstand this, so perhaps you would expand on this ??
  3. endy, +1 for tenacity
  4. The Ancient Greeks didn't do much 3D geometry but this particular result was due to Archimedes, though his approach and proof was rather different. The area is the same on an equivalent cylinder. Pity you didn't put that working into a spoiler, but well done for working it out.
  5. When you guys have fully conquered 2D how about tackling 3D? Same problem but on a sphere not a circle. If you paint parallel stripes on a football so that in fiveworlds' post#4 each of A, B C etc represent a painted stripe on the football. How do you relate the area of paint to width / height of the stripes ?
  6. Hammers are good for you. source: http://www.marksdailyapple.com/sledgehammer-workout/#axzz41YXPIOaX
  7. Have you considered that there are other forms of rudeness besides direct insults, some of which are particularly counterproductive? Do you not consider it rude to post a question you clearly desire the answer to; for someone else to put possibly considerable time and effort into constructing a cogent reply, for the originator never to return. I post here to help others but I sometimes wonder if it is worth ever helping anyone again.
  8. The pictures are very pretty, can we see your attempt at the problem?
  9. So am I. How can an acceleration equal (the negative of) a velocity? Please check the wording.
  10. Here are some facts, figures and terminology. Source: Strahler, The Earth Sciences Meteoriods are tiny particles ravelling through space at high velocity. When they enter the Earth's atmosphere they become meteors. These are characterised by their luminous trails in the sky. They range in mass from .000001 to .001 kg and enter tha atmosphere at 25 to 80 km / second Nearly all burn up to gas in the upper atmosphere, 90 to 200 km above the surface. Because they are so small and so high, their destruction is accompanied by their luminous trails (50 to 100 km in length) , but no sound. Larger particles can make it all the way to the surface. These are called meteorites. These are accompanied by brilliant light and explosive sounds, especially upon impact. @Pavel another book you might find interesting http://www.amazon.co.uk/Atmosphere-Ocean-Our-Fluid-Environments/dp/0851412955
  11. I respectfully suggest you check up on some basic classical mechanics before messing with relativity. It is a physical impossibility to hit something (ball) that is travelling faster than you (bat) are in the direction of its motion. This applies in ordinary Newtonian mechanics, just a much. Of course you can hit the object by striking across its line of motion, but that cannot impart additonal motion in its direction of motion.
  12. Before it burned up of course.
  13. Here is some builders' maths I overheard recently. Larger sized nails ( 4" and 6") are packed in alternate directions in the box to save space. (So the heads and points are alternately at one end then the other) Two builders and their apprentice were fixing some roof timbers here is their conversation. Apprentice "Mick, why are you throwing half the nails away?" Builder1 "Look half the heads are on the wrong end" Builder2 "Don't be thick, they are for the other side of the house"
  14. Remember your meteor burns up. I suggest you are getting the scenario a little muddled up. If the meteor burns up it adds gas to the atmosphere. Momentum is very quickly distributed within gases. So the atmosphere as a whole then possesses the momentum originally owned by the meteor as well as the very much larger momentum it already had due to its attachment to the Earth system. Due to that attachment the momentum finally finds its way into the solid part of the Earth system. So yes, all the meteor's original momentum is transferred to the Earth system in the same way as when two bodies coalesce on impact.
  15. Actually it is impossible for another reason, accessible to any high school physics student. Let us suspend disbelief for a moment and accept the ball travelling in direction d at the speed of light. Now let us consider the conditions under which bat, b can hit this ball and impart additional momentum (velocity) in direction d. Well bat b must already be travelling faster than light in direction d or it could not catch the ball! But this is contrary to postulate, since nothing (material except the olive in the martini) travels faster than light.
  16. Good morning, Shawn, Yes you can use the same principle for reactive components, although the bridge is not then called a Wheatstone bridge. AC bridges suitable for inductive measurements include the Maxwell Bridege, The Schering Bridge and the Hay Bridge. In the general ac bridge, the DC battery of the wheatstone bridge is replaced by an ac source and you have to balance both the absolute magnitudes of the voltages and the phases [math]\left| {{Z_1}} \right|\left| {{Z_3}} \right| = \left| {{Z_2}} \right|\left| {{Z_4}} \right|[/math] and [math]\left( {{\theta _1} + {\theta _3}} \right) = \left( {{\theta _2} + {\theta _4}} \right)[/math] In general you would try to avoid more than one inductance in a bridge because they couple more readily than capacitors or resistors and what you require is self inductance not mutual inductance. One alternative to bridges for inductive measurements is the Q meter. Another is to use the impedance of the inductor to modify the feedback factor of an op amp.
  17. I think MigL was referring back to your post 1 and the pin point v the pin head. If you push the head against the melon with the same force as you push the point the pressure applied will be greater at the point. But there are other factors in play such as surface hardness. These are exploited in industrial standard hardness testers (Vickers, Brinell etc) https://www.google.co.uk/search?hl=en-GB&source=hp&biw=&bih=&q=hardness+testing&gbv=2&oq=hardness+testing&gs_l=heirloom-hp.1.0.0l10.1766.5906.0.7484.16.10.0.6.6.0.172.1203.0j8.8.0....0...1ac.1.34.heirloom-hp..2.14.1453.XJ_r7KaExYo
  18. I do wish popsci stopped offering this picture. In order to bend in 4 dimensions, 3D space must be embedded in a 4D universe. We have no evidence of the existence of this 4th dimension. The 'bending effect' is due to mathematical transformations between the various points that are all in 3D space only. The amount of 'bend', ie the values of the coefficients in the transformations, depends upon the amount of mass and energy and its distribution around the 3D points. With no mass or energy present there is no bend, but when it is the distribution also controls the variation of the bend with direction, through the coefficients.
  19. A good discussion to have, +1 You have obviously been reading the later posts in this thread http://www.scienceforums.net/topic/93683-whats-the-definition-for-this-law/ Your next challenge will be reading a Doctor's hanwritten notes.
  20. Answer to both, Yes, of course, but the wall velocity remains at zero and the force developed is rate of change of momentum. Edit Remember also that a speeding solid body (meteor) striking a (relatively) stationary fluid is the same as a speeding fluid striking a (relatively) stationary solid body (wall).
  21. Can I come to you for spelling lessons, endy? Thanks. +1
  22. Well I started this thread to share information about something that will affect most over the coming years. So here is my latest installment. Last week I was called to fix a failed accounts PC in a small aerospace manufacturing company. We agreed the best solution was to replace and discussed with Sage and HMRC about the virtues of W7 v W10. We were assured that the Accounts, Payroll and Tax packages would run happily on W10 so we should go for this. Naturally we needed the pro or business version and like many businesses had been waiting for this to appear. Now we deal with the largest trade supplier of electrical and electronic equipment and components in Europe and I had just received the February 2016 update to their current 4000 page catalogue. Great, I thought, A new range of lenovo W10 business machines, ready to go with W10 loaded. Better a range of W10 installation disks for sale! Better yet, 5 in stock. So I ordered one, with intention of getting the rest if it proved satisfactory. Roll on this Monday (didn't Abba write a song about this?) When I went to install the new machine, guess what. Yup still W7 in the box, although it was labelled W10 and had a W10 licence. No it was not a mistake, The supplier's Technical Director said "We only move boxes, We are not responsible for what is in them" And the installation disks. Well they are just figments decorating the catalogue pages.
  23. Actually it does. The mechanical device similar to using the blunt end is called a (cone) penetrometer and is used in to asses the bearing capacity of soil. https://www.google.co.uk/#q=cone+penetrometer This measures the pressure applied and resisted. Pressure is a direct stress, not a shear stress and does not lead to rending division of the material, as does shear stress. The sharp end of a tool causes rending, not squashing.
  24. Hi, Pavel. Firstly be careful talking about a wave. Waves have no net momentum to transfer. You mean a pulse. Secondly as the meteor traverses the atmosphere it exerts a ffrictional force on the atmosphere (and the atmosphere on it) . This force appears as a result of the destruction of its linear momentum in that direction. This is similar to the destruction of forward momentum when a liquid jet impacts upon a wall. The science of momentum transfer and exchange (in this context) is called transport phenomenon and the classic text is Transport Phenomenon Bird, Stewart and Lightfoot IMHO it is one of the best textbooks ever written on any technical subject.
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