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. H

    Confusion about partial derivatives

    Dear all, I have a confusion about partial derivatives. Say I have a function as y=f(x,t) and we know that x=g(t) 1. Does it make sense to talk about partial derivatives like \frac{\partial y}{\partial x} and \frac{\partial y}{\partial t} ? I doubt, because the definition of...
  2. R

    Line integral - confusion on squares and square root terms

    line integral -- confusion on squares and square root terms Homework Statement Do you see where they have sqrt(16 sin^2t etc = 5? How do they get that, the answer should be 7, the square root of 16 is 4, sin^2 + cos^2 is 1 and the square root of 9 is 3, 3 + 4 = 7. It's like they're...
  3. MartinJH

    Confusion with time dialation.

    Reading Brian Cox and Jeff Forshaw's book "Why does E=MC2". They mention that satellites speed up with time, but, then reading Wiki it says the crew of the ISS experience the slowing of time. Which one is correct? I'm slightly confused. Both experience a weaker gravitational pull and high...
  4. S

    Reimann Integral definition confusion.

    My lecture notes say: Let f:[a,b]->R be bounded. F is said to rienmann integrable if: L=\int_{a}^{b} f(x)=U where : L=Sup(L(f,P)) and U=Inf(U,(f,P)) but everywhere else(internet) there's a definition with epsilon. I have the epsilon stuff later under "riemann...
  5. D

    Confusion in thermal radiation concepts - infrared, microwave, etc.

    Microwaves heating is often referred to as dielectric heating, but I'm not sure why this seems so special to specify of all the different thermal radiation frequencies. Doesn't infrared heat the dielectric material as well in a similar process? Isn't radiation heat transfer common for a wide...
  6. W

    Understanding Bayes' Theory: Examples and Confusion

    I'm struggling with Bayes' theory. Please consider the following: Example 1: Submarine sinks if one missile hits it. Two ships aim at submarine and fire one missile each. Ship 1 shoots missile X1, ship 2 shoots missile X2. P(X1 hitting = 0.8) P(X2 hitting = 0.5) P(X1 and X2 hitting | submarine...
  7. D

    Green's Theorem & Line Integral confusion

    Homework Statement a) Evaluate the work done by the force field F(x, y) = (3y^(2) + x)i + 4x^(3)j over the curve r(t) = e^(t)i + e^(3t)j, tε[0, ln(2)]. b) Using Green’s theorem, find the area enclosed by the curve r(t) and the segment that joins the points (1, 1) and (2, 8). c) Find the...
  8. A

    Does the Unruh Effect Contradict Energy Principles in Flat Spacetime?

    I have a question about the Unruh effect. For the spacetime to be flat, it must contain no energy. But the Rindler observer is supposed to be eternally accelerating, which would require infinite energy. Is there an obvious resolution to this apparent contradiction?
  9. H

    Confusion on sign convention for surface integrals

    Homework Statement Compute the surface integral for F = [3x^2, y^22, 0] and S being a portion of the plane r(u,v)=[u,v,2u+3v], 0≤u≤2, −1≤v≤1.The Attempt at a Solution I managed to get the correct answer, because with some luck I defined the normal in the correct direction. I am just confused...
  10. A

    Fundamental thermodynamic relation confusion.

    dE = dQ + dW = dQrev + dWrev = dQirev + dWirev. We have for an reversible process, dQrev = TdS and dWrev = -PdV. So; dE = TdS - PdV So this relation is for all changes (irreversible or reversible) since dS and dV are state functions. What doesn't make sense to me is the next part when...
  11. binbagsss

    SHM spring system, Tension direction confusion.

    Say a spring is on a horizontal table, and the particle is initially at the midpoint of the spring in equilibrium, and then the particle is displaced to one side. I have attached a diagram, let this side be more to A. Then I am confused as to which direction the tension in both sides of...
  12. M

    Some Confusion with an Exponential Equation

    I'm reviewing for my final exam so one of the practice problems is: 5= 3^(x+5) Here's my attempt at it: ln 5= x+5 ln 3 ln 5 / ln 3 = x+5 (ln 5 / ln 3)-5= x 1.46-5 ≈ x -3.54 ≈ x I checked my answer and I get 3^1.46 ≈ 4.97 so rounding it up gives me 5 since I rounded off 1.46...
  13. H

    A little confusion over x and y values

    Suppose a function is defined as: f(x,y)=0 for x=y=0 Does this mean that the function would be zero when both x and y are xero or when either one of them are zero?
  14. Z

    Conceptual Area Under Velocity-Time graph confusion

    Hi all I have a confusion regarding a physics concept. When you consider area under graph (velocity time graph), if the area is below x axis, is the area considered to be negative? For example, look at the attachment. There are 2 shaded areas. Let the area above x-axis be A and area below...
  15. I

    Confusion: computation of class number of K=Q(sqrt(30))

    As an exercise, I'm trying to compute the class number of K = \mathbb{Q}(\sqrt{30}). By the Minkowski bound, I just need to consider the prime ideals which divide 2,3,5. I've found that (2) = \mathfrak{p}^2_2 (3) = \mathfrak{p}^2_3 (5) = \mathfrak{p}^2_5 where...
  16. A

    Understanding the Lorentz Equation: Clarifying the Confusion

    I am confused of how to derive the Lorentz equation x = vt+x'/γ...if x' is the distance to an event according to O' and x is the distance to that same event according to O, then shouldn't the last term be x'γ not x'/γ, since x' is already contracted according to O, so to relate it to x, we would...
  17. F

    Confusion over notation for finding limits

    I don't know how to properly present my answer to find the limit of a converging sequence like (1/2)^n. I would just write something like this... y=1/x+1, x=∞ } y=1/∞+1=0+1=1 but the syllabus gives something completely different and my textbooks don't seem to cover this portion of the...
  18. E

    Is Negative Work Possible with a String?

    Shouldn't there be negative work done by the string?
  19. V

    Confusion in using KVL (assigning polarities) in a problem

    This is actually a solved example of Thevenin's principle in my textbook and I understand all of it except the part that I'm attaching to this post below; the part where KVL (Kirchoff's Voltage Law) is applied. Homework Statement Find Eth in the circuit shown in the attached figure...
  20. G

    Confusion About Simple AM Radio Receiver/Tuner

    I am confused by the design of this AM receiver/tuner circuit. http://imgur.com/f9n05 I don't understand how the inductor and capacitors on the left design a circuit that resonates at a certain frequency, and I also don't understand why the resistor and capacitor in parallel after the diode...
  21. L

    Confusion between orthogonal sum and orthogonal direct sum

    For 2 vector spaces an orthogonal direct sum is a cartesian product of the spaces (with some other stuff) (http://planetmath.org/encyclopedia/OrthogonalSum.html ), and this orthogonal direct sum uses the symbol, \oplus. However, there's an orthogonal decomposition theorem...
  22. mcodesmart

    What is the Relationship Between Seebeck Coefficient and Temperature Gradient?

    The Seebeck coefficient is the differential drop in voltage per unit temperature across a conductor. Goldsmid says that there must be a temp. gradient across a junction for a seebeck coefficeint to be defined. This makes sense if the difference in the fermi level energy between two dissimilar...
  23. M

    How do power and velocity affect acceleration in a moving car?

    Hi! I'm extremely confused by this problem. A car of mass 1200 kg starts from rest and travels along a horizontal straight road. The engine of the car develops a constant power of 54 kW. All the energy produced by the engine goes into increasing the kinetic energy of the car. The questions...
  24. B

    A confusion related to Significant figures

    A book says," 0.00052 has two significant figures: 5 and 2" Now imagine a scale to measure length and suppose it's least count is 0.00005 we measure a length and it comes out to be 0.00052 where we are uncertain about the last digit. So if i am understanding the meaning of sig. figures right...
  25. J

    What is the role of binding energy in fission and fusion reactions?

    Homework Statement What exactly is binding energy? why is this energy RELEASED during fission / fusion Homework Equations The Attempt at a Solution when two light nucleons fuse they combine to form a heavier nucleon whose mass is less than the sum of the two separate nucleons. This...
  26. F

    Implicit differentiation - major confusion

    Hello. I know how to do implicit differentiation taught in calculus 1, but I'm confused by something regarding it. Take the example: y3+y2-5y-x2=4 If we do implicit differentation we get: 3y2(dy/dx)+2y(dy/dx)-5(dy/dx)-2x=0 dy/dx=2x/(3y2+2y-5) Now, it makes sense how to...
  27. E

    Are Resistors in Parallel if Another Resistor is Between Them?

    For the circuit shown, is the 3 ohm resistor in parallel with the 5 ohm resistor if the 1 ohm resistor is "in the way?"
  28. M

    What Are Orbits, Subshells, and the Shielding Effect in Chemistry?

    I was reading my textbook and was confused on the terminology, is an orbit each of those boxes that you fill up with the up and down arrow, and the subshell is like s, p, d, f, g, h? I was also confused about what the shielding effect is. If anyone can enlighten me that would be great, thanks
  29. E

    Parametric equation confusion of d2y/dx2

    x=t2 and y=t3-3t, find dy/dx and d2y/dx2 I understand how to get to dy/dx but an confused on how to get to d2y/dx2 can someone please explain in depth, I know the formula is (d/dt dy/dx)/(dx/dt) I don't understand where d/dt comes from and what it is. why do we not just derive it twice? I...
  30. M

    Radiation calculation confusion

    Homework Statement 6. If the exposure rate from 137Cs at one metre is 2.50 mGy/h, how many bequerels are present? Homework Equations Exposure is a quantity that expresses the radiation delivered to a point at a certain distance. I1d12 = I2d22 I1 = the radiation intensity at...
  31. S

    Can the Big Rip affect virtual particles' annihilation process?

    Layman here. Two questions on Virtual Particles. I am not trying to make some claim to spontaneous generation, just curious about how to expand the holes in my knowledge... which is about the level of a post grad engineer who likes to buy the popular physics books in stores to read. 1)...
  32. U

    Conversion confusion: Rankine in ideal gas constant

    Hi all. I have ran into a problem in converting from imperial to SI units, as follows. The ideal gas constant for air is often given in imperial units as R = 1716 \frac{ft*lbf}{slug*°R} where 1 ft*lbf = 1.356(10^{-3}) kJ 1 slug = 14.59 kg °R = \frac{9}{5}K Thus making these...
  33. S

    Confusion about quantum foam, quantum gravity and singularities

    Hi all, I've just finished reading a book about Black holes (Black holes & time warps, by Kip Thorne) and there's something in particular I'm confused about. One chapter talks about what can possibly be inside the singularity, specifically what would happen to an astronaut as he falls...
  34. C

    Is 3500 lb/in Referring to Force per Inch of Width?

    Hi all, I have a spreadsheet which says failure will occur in my composite piece when a load of 3500 lb/in is applied. If I were to tensile test this piece and the thickness has already been input (0.138 in) does this mean for every inch wide the piece can take 3500lb of force? That seems...
  35. M

    Confusion over intensive properties (Thermo)

    Disclosure: I am studying biochemistry so my thermodynamics education is lacking and I'm likely misinterpreting some of these concepts (that's why I'm here for help). I have always had trouble defining some properties as either intensive or extensive. I understand that extensive are...
  36. O

    Maxwell's, integrals, current, elements, delta phi and confusion

    I'm working on an online EECS course, and to be frank some of it is going straight over my head - but at the same time parts of it are far below my current knowledge, so I want to work and stick with it. The speaker is working through proving current and voltage - to arrive at Kirchoff's...
  37. E

    Shorting neutral to Earth confusion

    what will happen if i short neutral ac outlet wire with earth? please see the figure if you have any confusion.
  38. Doofy

    I have some confusion over neutrino oscillations?

    I'm trying to learn the basic theory of neutrino oscillations at a postgraduate level. I have a few things that are bothering me. 1) All of the papers & textbooks I have looked at start out by just assuming that each neutrino flavour eigenstate is a superposition of the mass eigenstates...
  39. J

    Gradient Confusion: Explaining Gradients in Layman's Terms

    Hi I am having trouble getting my head around the definition of a gradient. I know a gradient tells us the direction of steepest slope that one must follow to arrive at a maximum and I know it is defined as: However I haven't got a gutt feeling for it, I need these questions answering...
  40. A

    Calculating nth Derivative of e^ax cos(bx+c)

    My question is about the nth derivative of e^ax cos(bx+c). Though i can calculate it easily but i am confused at one point. When we calculate the first derivative we put a = r.cos(theta), b = r.sin(theta) (every thing is ok till here) My confusion starts when we use (theta) = tan^-1(b/a) [tan...
  41. B

    Confusion about linear equations

    Hi everyone! 1. Is a linear equation the same as a polynomial of first(or 0th) degree? 2. The book 'Mathematics for physicists and engineers' by springer(publisher) states that an example of a linear (DE) equation is 5.dy(x)/dx = x.y(x). Yet I read somewhere else that f(x,y)=a.x.y+b is not...
  42. M

    Confusion about synchronization

    Hello, Suppose, in moving train Observer O is at middle point M, and two clocks is situated at A(rear) and B(front). O has a clock. I have confusion about time of A and B after synchronization. I have two scenario, please, tell me which one is right. (1) If we assume that one way...
  43. J

    MHB Confusion with variables when solving a recurrence equation

    If I have a recurrence equation of the following form: $$T(n) = T(km) = a, m = 1$$ $$T(n) = T(km) = T(k) + T(k(m-1)) + cn, m > 1$$ Where a is simply a constant, and k is an integer constant > 0. Now I begin substituting to find the pattern: $$T(k) = a$$ $$T(2k) = a + [a] + c2k$$ $$T(2k) = 2a...
  44. N

    Confusion about calculation of aerodynamic moments

    Hello, Can anybody explain how the aerodynamic moment is calculated for an airfoil ? I was reading the first chapter in "Fundamentals of Aerodynamics" by Anderson & the formula for aerodynamic moment for the lower surface of the airfoil confused me. Is the aerodynamic moment calculated about...
  45. T

    Confusion on Concept of Electric Potentials/Potential Energy

    I am a bit confused about electric potentials and potential energy. There are three key situations that are giving me trouble: 1) If an electron is midway between to protons, the potential energy is -ke2/r for both, and thus the total electric potential energy is twice that value. I see...
  46. 2

    Clear up some cross product confusion for me

    Here is what I have A=xro+yr1 B=yro+xr1 I need to find A x B I am confused about do it because The components of A and B are in terms of vectors If A = 3i + 4j + 7k and B = 2i + 2j + 1k I would have no problem (these numbers are meaningless just giving an example) finding A...
  47. B

    Ion naming confusion with the bi prefix

    Ion naming confusion with the "bi" prefix I am little confused on when you use the "bi" prefix to denote the existence of a proton in front of an oxyanion. For example, I know that [HCO_{3}]^{-} is called bicarbonate as well as hydrogen carbonate. A problem arises when I try to define...
  48. N

    Pauli's Role in Band Structure: Confusion or Clarity?

    "Band structure a result of Pauli"? Professor hopelessly vague or in essence correct? Hello, I'm taking an introductory course on Solid State physics (level: last year undergrad physics) and the professor said one can view the band structure in solids as a result of the Pauli principle...
  49. A

    Confusion in understanding Taylors theorem.

    I know that Taylors theorem is used to expand f(a+h) in terms of f(a) and its derivatives in the interval (a,a+h), but my question is that can we use it to expand f(a-h) in terms of f(a) and its derivatives over the interval (a-h,a). If yes please give reason.
  50. F

    2nd order DE largest interval confusion

    2nd order DE..."largest interval" confusion Homework Statement Determine the largest t-interval on which therem 3.1 guarantees the existence of a unique solution: y'' + 3t^2y' + 2y = sin(t) ...y(1) = 1 ...y'(1) = -1 Homework Equations theroem 3.1 is the one that states if p(t)...
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