Confusion Definition and 1000 Threads

In medicine, confusion is the quality or state of being bewildered or unclear. The term "acute mental confusion" is often used interchangeably with delirium in the International Statistical Classification of Diseases and Related Health Problems and the Medical Subject Headings publications to describe the pathology. These refer to the loss of orientation, or the ability to place oneself correctly in the world by time, location and personal identity. Mental confusion is sometimes accompanied by disordered consciousness (the loss of linear thinking) and memory loss (the inability to correctly recall previous events or learn new material). The term is from Latin: confusĭo, -ōnis, from confundere: "to pour together", "to mingle together", "to confuse".

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  1. D

    Electricity and magnetism confusion

    Homework Statement I've been set an assignment and I'm struggling with one question in particular: Homework Equations 'Use the following data and plot the graphs for a point charge' 'Plot graph of E against r^2. Interpret the graph to describe electric field strength and electric...
  2. T

    Confusion about Christoffel Symbols

    In the book Mathematical Methods for Physics and Engineering by Riley, Hobson, and Bence, I came across an equation I just can't seem to understand. In the chapter on tensors, they derive the equation for a Christoffel symbol of the second kind, \Gamma^{m}_{ij}=\frac{1}{2}g^{mk}\left(\frac{...
  3. M

    Confusion regarding Residue Theorem

    So I ran into residue theorem recently and found it to be pretty amazing, and have been trying to get some of the more fundamental aspects of Laurent series and contour integrals down to make sure I understand it properly, but there's still one big aspect that keeps confusing me majorly...
  4. D

    Confused about Current Flow & Capacitances

    I have some doubts regarding Current Flow and Capacitances... I Read this somewhere.. " an electrochemical cell supplies energy to move a charge from its low energy, low potential terminal to the high energy, high potential terminal. In this sense, the cell supplies the energy to establish...
  5. F

    Focusing at infinity for a camera and circles of confusion

    Hello Forum, when a camera is focused at "infinity", everything from infinity on is in focus (acceptable). How is that possible? Every plane that is not in perfect focus has a certain circle of confusion that gets larger (more blurring) as we move away from the best focus plane... Also...
  6. S

    Quantum Key Distribution confusion.

    Hey, I'm slightly confused on a part of the process of Quantum Key Distribution (E91 protocol). I have something which tells me how Alice would send a message to Bob. An atomic transition from an outside source would produce 2 photons both with the same circular polarisation. One of these is...
  7. C

    Confusion from Weinberg's QFT vol1

    Hello! I came across with something that confused me while studying the book and I need some help. In section 7.3 , equation (7.3.4) should have the drivative of ε(x) in order to "vanish when ε(x) is constant" . But in the lines before this expression he says that the variation of action...
  8. S

    Why Does Temperature Remain Constant in Adiabatic Free Expansion?

    Homework Statement We start with an ideal gas confined to half a container. Then, without heat flow, the gas flows into the other half as the partition is punctured. Find the new temperature after the expansion. Homework Equations Since there is no heat flow, I assume the process is...
  9. M

    Confusion over Rolling with Friction and Rolling Without Slipping

    Homework Statement This isn't a specific question, more of a general one: Suppose there is a cylinder of mass m that is rotating in the positive clockwise direction with initial rotational velocity \omega_0, and radius R. Then, suppose this rotating cylinder is placed on a surface with...
  10. Z

    Confusion about Fraunhofer Diffraction

    I'm looking at the explanation for single slit Fraunhofer diffraction, in particular the location of the intensity minima. a is the slit width, lambda is the wavelength and theta is the angle. By dividing the slit into two parts and viewing the wavefront as a sum of many small sources i can see...
  11. A

    Conservation of Angular Momentum and the Role of Coordinate Systems

    Imagine i have a particle in the xy plane rotating in a circle around the z-axis at a constant angular velocity. The angular momentum is r cross p which would give me a constant value at all times, there is no change and it's conserved. However if I was to move the rotating particle higher up...
  12. P

    Air resistance, dimensional analysis confusion

    Hi. Consider the basic eq for a falling body with air resistance dv/dt=g-kv/m I don't understand air resistance as a force, since it seems irreconcilable to the force equation F=ma. How is a force a function of velocity? I am also not sure how this equation makes sense in terms of...
  13. D

    Rotational Dynamics Confusion

    I am right now studying Rigid Body dynamics.. I have some doubts regarding Dynamics... 1) When a body is rotating as well as translating...we say that every particle of the ..lets say ROD is moving with a resultant velocity = Vcm ( translational velocity of COM) + ω.R (where R is the...
  14. A

    Confusion abt relation betwn time travel and speed of light

    i don't know in which section it belongs, so i am putting it here... according to various theories proposed by various researchers, time travel depends on the speed of light. as far as i have read/heard - i) anything traveling faster than the speed of light moves back in time. ii) anything...
  15. S

    Clearing Up Units Confusion: How to Ensure Consistency for Density and Rotation

    Please can anyone help me?I'm confused here. If I'm following unit of force as Newton, and length as mm; and stress as MPa,then for a consistent system of units (see link below); http://www.dynasupport.com/howtos/general/consistent-units/ what should be the unit for: 1)density 2) rotation
  16. Femme_physics

    How Does a Missing Component in the Feedback Loop Affect the Transfer Function?

    I'm confused by the fact there's nothing in the feedback loop here http://img706.imageshack.us/img706/6075/feedbackloop.jpg For instance, if I had "H1" in the feedback loop I'd do C/R = (Gcs x Gps) / (1+H1) But since I don't have H1... is it simply C/R = (Gcs x Gps) / 1 = Gcs...
  17. R

    Lateral inversion up-left and down-right confusion

    Hi :) So I'm learning about lateral inversion in plane mirrors and it's a bit confusing. I think of it like this:- Suppose you had a clone of your self who is standing next to you and facing the same direction. He walks a few steps forward and then turns to face you. When he turns to face...
  18. I

    Confusion with definition and notation of reciprocal.

    Hello everyone, I have some conceptual issues with aforementioned definitions. How is exactly multiplicative inverse defined? Say, for a rational, nonzero number a/b, its reciprocal is b/a. Is there a certain operation that transforms a/b to b/a? Also, the notation for multiplicative...
  19. C

    Confusion on this logarithmic equation NEED HELP

    e^(3+2logx) = (3x-2)*e^3 I can get down to this point: e^(logx^2)=3x-2 I have checked the solution in the book, and the steps. Turns out it simplifies to x^2 -3x +2=0. The problem is I can't figure out how I pass from e^(logx^2) to x^2, because as far as I know logx isn't the same as lnx...
  20. P

    KVL Confusion: Voltages & Arrows Explained

    http://www.flickr.com/photos/53512951@N06/8229416013/in/photostream/ With regards to the circuit in the image linked above, I have been told to start in the bottom left hand corner and then work clockwise around the circuit, adding up all the voltages to see if they follow the KVL principle...
  21. M

    Confusion regarding differential forms and tangent space (Spivak,Calc. on Manifolds)

    I have been working through Spivak's fine book, but the part about differential forms and tangent spaces has left me confused. In particular, Spivak defines the Tangent Space \mathbb R^n_p of \mathbb R^n at the point p as the set of tuples (p,x),x\in\mathbb R^n. Afterwards, Vector fields are...
  22. J

    V, I, R in series circuit confusion

    I'm doing coursework on a circuit experiment we performed in class. I'm pretty sure the results are wrong or flawed, but we were testing the effect of increasing the length of wire on the resistance. I had a voltmeter about the wire, a cell, an ammeter, and completed the circuit by attaching the...
  23. DocZaius

    Sx acting on up spin particle confusion

    I am reading Griffiths and I am having trouble interpreting the results of measuring the x component of spin on a spin-up particle. If you have a spin up particle, my understanding is that it is assumed to be up in the preferred axis, z. I would think that measuring its x component should...
  24. E

    Leg Presses Work Energy Theorem Confusion

    Homework Statement As part of your daily workout, you lie on your back and push with your feet against a platform attached to two stiff springs arranged side by side so that they are parallel to each other. When you push the platform, you compress the springs. You do 80.0 J of work when...
  25. E

    Confusion about springs and hooke's law

    There is a statement in my book i can't really understand. "To stretch a spring, we must do work. We apply equal and opposite forces to the ends of a spring and gradually increase the forces. We hold the left end stationary, so the force we apply at this end does no work.The force at the moving...
  26. X

    Confusion about redshift in a universe with accelerating expansion

    Hello, I've been trying to internally conceptualize as much of physics as I could, and doing so I realized that something I thought I understood at first does not actually make any sense in my head anymore. And since it doesn't, I'm afraid that I might have misunderstood a lot of other concepts...
  27. A

    How Much Distilled Water to Add for Dilution Using c1v1 = c2v2?

    Homework Statement Determine how much distilled water must be added to 250 ml of a 1.5 M solution of Na2CO3 to dilute it to a concentraion of 0.5 M. Homework Equations c1v1=c2v2 The Attempt at a Solution I'm having trouble understanding how to identify c1,v1,c2, and v2, especially since every...
  28. T

    Why are all non-principal sagittal rays considered skew?

    According to Wikipedia: The part I don't understand is why all rays that are sagittal rays that are not the chief/principal rays must be skew. Do they just mean all other rays originating from the same object point must be skew? Because that makes sense. Are these things always discussed...
  29. AakashPandita

    Utter confusion regarding distance covered during acceleration in free fall.

    Let there be an obj. which is made to fall from a certain height in a gravitaitonal field. where a= 10 metre per second squared Say it falls for 1 second. v(final velocity)= 10 metre per second. How much distance does it cover in that 1 second? distance = speed x time = avg...
  30. K

    F=ma Confusion about answer given for F

    Hi, I'm reading a book and one of the questions asks: how much force is required to give an object weighing 3000lb an acceleration of 12ft/sec2? I calculated this as F=3000x12=36,000pdl. The answer given is "1125 force" (36,000/32). Why is this? Why isn't it just 36,000pdl?
  31. T

    Fission/Fusion reactions confusion help

    Fission/Fusion reactions confusion help please Homework Statement http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_s03_qp_4.pdf number 6...
  32. M

    How do congruences work in mod arithmetic?

    Hi, this is not a homework problem, i just have a hard time following the sequence of this In the book , it shows a couple examples (=== is the triple equal sign) 1) 26=19+7===3+7===10(mod8) 2) 15=19-4===3-4=-1(mod8) 3)38 = 19*2===3*2=6(mod8) 4) 7===2(mod5), 343=7^3===2^3=8(mod5) I...
  33. A

    What is the relationship between weight and g-force in determining F?

    Hi. Can you clarify for me the equation for g-force below: F= ma + mg I got this equation from my lecturer. He asked the class to determine how was the formula above formulated. But this is not a homework. Is the equation above true for g-force? If it's true, how does...
  34. K

    Confusion (8) from Weinberg's QFT.(Lippmann-Schwinger eqn)

    I was reviewing the first few chapters of Weinberg VolI and found a hole in my understanding in page 112, where he tried to show in the asymptotic past t=-\infty, the in states coincide with a free state. In particular, he argued the integral \int...
  35. F

    Small confusion about an improper integral example.

    We have that \int^{1}_{0}\frac{1}{\sqrt{1-x^{2}}}=lim_{\stackrel{}{t \rightarrow 0^{+}}}\int^{1}_{t}\frac{1}{\sqrt{1-x^{2}}}=lim_{\stackrel{}{t \rightarrow 0^{+}}}[arcsin(x)]^{1}_{t}=\frac{\pi}{2} However, I think \int^{1}_{0}\frac{1}{\sqrt{1-x^{2}}} should equal to lim_{\stackrel{}{t...
  36. M

    Nodal analysis: simple confusion

    My question about this excercise is the 80+20 part in the denominator. Why and when do I do that? I tried doing it but got the wrong answer
  37. S

    What are the different ways bonds can be represented?

    In the following link http://en.wikipedia.org/wiki/File:Silicon-tetrafluoride-2D-dimensions.png the bonds are represented pictorially in different ways(like the black triangle). Do these just show the physical structure of the bonds or do they show the different types of bonds?
  38. M

    Confusion about continuity question.

    1.The Question The function f(x)= x2/x if (x≠0) 0 if(x=0) The Attempt at a SolutionI thought this had a removable...
  39. L

    Natural Unit Confusion: M=1/L or M=T/L^2?

    If we set c=G=1, then c=1 leads to L=1/T , the G=1 means that M=L^3/T^2 and combining the two means that M=L=1/T so far so good. But say if I also want \hbar=1 this seems to imply M=T/L^2 but combining this with c=1 which gave the L=1/T now suggests that M=1/L=T . Which seems...
  40. D

    Why Aren't Partial Derivatives Written with Respect to Composite Variables?

    Let g(t) = f(tx, ty). Using the chain rule, we get g'(t) = (\frac{\partial f}{\partial x})(tx, ty) * x + (\frac{\partial f}{\partial y})(tx, ty) * y this was actually part of a proof and what i don't understand is that why didn't they write (\frac{\partial f}{\partial (tx)}) and...
  41. S

    Why is oceanic crust thinner than continental crust?

    Hi, I am doing a geophysics assignment and had some confusion. Basically I want to know why oceanic crust is so much thinner than continental crust. My friend has told me it's because there is less weight on top of it because the ocean water is not very dense, causing the mantle to rise up...
  42. L

    Confusion with dB equation - 10 or 20?

    how do you know when to use dB= 20log(ratio of input/output quantities) or dB=10log(ratio of output and inout). voltage seems to be 20, power seems to be 10... but how about when doing Fourier transforms and you want to find out 3dB of maximum, for example? thanks
  43. S

    Confusion about Unit Cell Structure: Understanding Lattice and Basis Vectors

    Greetings everyone, I am taking a course on elementary condensed matter physics and our textbook is "Introduction to Solid State Physics" by Charles Kittel. I have read the crystal structure from 4 books; however, I am still confused about the definitions such as unit cell, primitive vector and...
  44. F

    RLC Circuit Calculations - How Do Wattmeters Work?

    Homework Statement There are two circuits I don't entirely understand. I am also new to calculations with complex numbers and when to and when not to use them, so be easy on me. Anyways, the point is to find out what the different meters are showing, when you are given the initial voltage and...
  45. D

    Why Do Different Kinematic Equations Yield Different Results for Free Fall?

    Homework Statement Upton Chuck is riding the Giant Drop at Great America. If Upton free falls for 2.6 seconds, what will be his final velocity and how far will he fall? Homework Equations The Attempt at a Solution Finding V(final)= Vf-Vi = at ---> Vf = (-9.81)(2.6) = 25.5 The...
  46. S

    Diffraction Transverse Wave Confusion

    http://en.wikipedia.org/wiki/File:Doubleslit.gif As shown in the link, diffraction is shown in the form of these kind of longitudinal waves. The diffraction pattern explains the wave interference pattern observed in the double slit experiment. However in the case of the delayed choice double...
  47. M

    Understanding Units of Work in Physics: A Brief Explanation

    Hey there, I'm in a math class and we're covering some applications to physics and although I completely understand the math behind it and am getting the correct answers, I'm a little iffy on how some of the units work. Would anyone be kind enough to tell me whether or not my thought process...
  48. A

    How Should a Swimmer Cross a Rapid River to Minimize Downstream Travel?

    Homework Statement 1)A swimmer wishes to across a swift, straight river of width d. If the speed of the swimmer in still water is u and the speed of the water is v (> u), what is the direction along which the swimmer should proceed such that the downstream distance he has traveled when he...
  49. P

    Semiconductors: P-N junction and carriers density confusion

    Homework Statement Hello PF, this is my first post (however I lurked here a few times). This comes from a lab I recently did. In this lab, we measure the current and voltage at a fixed temperature, in order to make an I(V) graph of a diode. Then, from this data and equation (1), we managed...
  50. D

    Cantilever, pin and UDL confusion

    So I have a 10 metre cantilever with a pin in the middle There is a roller at the end and a UDL of 10 kN / m acting across. Drawing the BMD is confusing me. By my calculations; there should be a 50 kN load acting at the fixed end and roller. Hence shape of the shear force diagram would be...
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