What is Sign: Definition and 592 Discussions

A sign is an object, quality, event, or entity whose presence or occurrence indicates the probable presence or occurrence of something else. A natural sign bears a causal relation to its object—for instance, thunder is a sign of storm, or medical symptoms a sign of disease. A conventional sign signifies by agreement, as a full stop signifies the end of a sentence; similarly the words and expressions of a language, as well as bodily gestures, can be regarded as signs, expressing particular meanings. The physical objects most commonly referred to as signs (notices, road signs, etc., collectively known as signage) generally inform or instruct using written text, symbols, pictures or a combination of these.
The philosophical study of signs and symbols is called semiotics; this includes the study of semiosis, which is the way in which signs (in the semiotic sense) operate.

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  1. binbagsss

    Weak Field Approximation - Quick Sign Question

    http://www.mth.uct.ac.za/omei/gr/chap7/node3.html Shouldn't eq 45 have a minus sign, looking at eq 29. Although I'm confused because the positive sign makes sense when comparing with the Newton-Poisson equation. I can't see a sign error in eq 29. (I believe the metric signature here is...
  2. P

    Holding Up a Sign: Static Equilibrium Force and Torque

    Homework Statement You are holding a sign as shown below. The sign (including the horizontal bar it hangs from) has a mass of 1.80 kg and is 36.5 cm wide. The sign is hanging from a 1.30 m tall, 4.16 kg vertical post. The sign is symmetric with a uniform mass distribution as implied by the...
  3. M

    What is the difference between curly and derivative (d) sign

    Dear All, Please see the image below in attachment where Energy is function of K. I want to understand how is it possible to understand the last expression ( dE = ? ). Additionally, what is the difference between curly and derivative (d) sign ? Many thanks to the mentors on this forum Best wishes
  4. V

    Passive Sign Convention Misconception?

    The Passive Sign Convention from Wiki: "In electrical engineering, the passive sign convention (PSC) is a sign convention or arbitrary standard rule adopted universally by the electrical engineering community for defining the sign of electric power in an electric circuit. The convention defines...
  5. A

    Electric Potential Energy and Sign

    There is a negative point charge with a positively charged plate above it and a negatively charged plate below it. Define up as positive and down as negative. When the point charge moves towards the positively charged plate it does negative work. Why? The force the charge experiences is upward...
  6. P

    Polar coordinates, sign ambiguity

    The position of a point in cartesian coordinates is given by: $$\vec{r} = x \hat{\imath} + y \hat{\jmath}$$ In polar coordinates, it is given by: $$\vec{r} = r \hat{r}$$ Now, ##x = r \cos{θ}## and ##y = r \sin{θ}## assuming ##θ## is measured counterclockwise from the ##x##-axis. Equating the two...
  7. J

    Sign of the Thevenin resistance equation

    Here is my problem: when trying to find Rth for a circuit with dependent sources, I excite the circuit a voltage Vo, and then proceed to find the resulting current Io. Finally, I use the equation Rth = Vo / Io, with a plus (+) sign. The way I see it, Io enters the positive side of Vo, so the...
  8. Mr Davis 97

    Can't get correct sign for a simple force problem

    Homework Statement A tension force of 2.50 N acts horizontally on a 2.00 kg block. The block accelerates at 0.750 m/s2. What is the force of kinetic friction? Homework Equations Fnet = ma = F1 + F2 + F3 + . . . The Attempt at a Solution I define the reference frame to be, in terms of an x...
  9. C

    Sign of Levi-Civita Symbol in spherical coordinates

    Hi, I am going through the derivation of an instanton solution (n=1) in Srednicki Chp. 93. Specifically, I went through eqn.s 93.29-93.38. However the sign of the Levi-Civita Symbol is bugging me: It says that in 4D Euclidean space, \epsilon^{1234}=+1 in Cartesian coordinates implies...
  10. binbagsss

    Einstein Equation Quick sign question

    Some sources seem to have: ##G_{uv}=8\pi G T_{uv} ## Whereas others have: ##G_{uv}=-8\pi G T_{uv} ## I thought that it may have been covered by how ##G_{uv}## is defined on the sources, but in both cases it is given as ## G_{uv}=R_{uv} - \frac{1}{2}g_{uv}R ## I'm confused. Thanks.
  11. P

    How to Keep a Sign from Collapsing

    Homework Statement . The sign shown below consists of two uniform legs attached by a frictionless hinge. The coefficient of friction between the ground and the legs is µ. Which of the following gives the maximum value of θ such that the sign will not collapse? (A) sin θ = 2µ (B) sin θ/2 = µ/2...
  12. kq6up

    Griffiths E&M and Convention of the Sign of Potential

    I am reviewing in Griffith's E&M, and I find that potential is defined as zero at infinity (that bits fine). However, should not an object that distance from a charge be less than zero (negative) if it is closer than infinity? It seems it should as it has lost P.E. However, he doesn't seem to...
  13. J

    Gravitational Potential Energy Sign

    I understand that GPE is negative, but it does not come out this way when i try to derive it. I took the change in potential energy in bringing a particle from an infinite distance to a distance of b from another particle. ## \Delta U = - \int \vec F \cdot d \vec r ##. Since the...
  14. H

    Sign of Frictional Torque in Pulley Equation

    Homework Statement A string passing over a pulley has a 3.80 kg mass hanging from one end and a 3.15 kg mass hanging from the other end. The pulley is a uniform solid cylinder of radius 0.04 m and mass 0.80 kg. It is found that if the heavier mass is give a downward speed of 0.20 m/s, it comes...
  15. S

    Sign swapping - spacelike intervals

    Hello guys! I´ve seen that for spacelike intervals, ie s^2 < 0 you´re able to swap the sign of s = x-y = y-x. Why is that? Thanks!
  16. H

    Do We Use Charge Sign in Electric Field Intensity Formula?

    Guys, when utilizing the electric field intensity formula ( Fe=qE), do we use the sign of the charge (q)? I think we do, but I remain confused!
  17. M

    Determining sign for variables

    I've attached the question along with its solution. It seems fairly simple yet the answer doesn't seem quite right to me. It appears as though they let downwards be + and that ## m\frac{dv}{dt} = mg + 0.4v## where v is negative since the ball is on its way up and there is a + instead of a - on...
  18. T

    Tensor moment of inertia -- why is there a "-" sign?

    why there is a negative sign in the tensor moment of inertia??
  19. Greg Bernhardt

    Anyone sign up with Obamacare yet?

    I'm sitting here a little depressed. I need to sign up my wife and I and the cheapest plan is $450/m with a $9000 deductible. We are both super healthy, rarely visit the doctor and were happy with our old catastrophe plans which were about $100/m each.
  20. Shindo

    Boy Holds 100N Sign Against Wall: How Much Push Force?

    Homework Statement If the coefficient of static friction between the sighn and his hands is 0.6, and the coefficient of static friction between the sign and the wall is also 0.6, with what force must the boy push to keep the sign in place? Homework Equations 0.6(Fn)=100 N Fn=166.7 N The...
  21. F

    MHB Did I misinterpret the sign attached to a term when factoring?

    I wanted to factor xy+x-2y-2 I got x(y+1)-2(y-1) and got stuck I tried somethings out and noticed (x-2)(y+1)=xy+x-2y-2 so how come I did get stuck? Did I extract the 2 incorrectly with the sign? For example should I have interpreted it at -2y-2 not 2y-2?
  22. M

    MHB Solving an integral using Differentiation under the integral sign

    I am Trying to solve the difference of the two following integrals: (1) $g_{1}(x) = \int_{0}^{\infty} \frac{cos(kx)}{k}\,dk$ (2) $g_{2}(x) = \int_{0}^{\infty} \frac{\exp(-2k)cos(kx)}{k}\,dk$ I read the thread on Advanced Integration Techniques and it...
  23. O

    Understanding Passive Sign Convention

    Problem statement I'm trying to understand how passive sign convention works, and how to read the voltages/currents direction in a circuit. For different set of voltages and currents I'm trying to calculate power. I'm using the picture below as a reference. a) i=10A v=125V b) i=5a v=-240V c)...
  24. S

    Which is correct: r1 and r2 should have different signs or be the same?

    Homework Statement referring to the notes attached , r1 is negative beacuse it's concave to the incident light , r2 is positive bacuse it's convex to the incident light. ( incident light move from left to right. ) , but my another book states that the r1 is and r2 have the same sign , which is...
  25. C

    Covariant Derivative Wrt Superscript Sign: Explained

    Dear all, I was reading this https://sites.google.com/site/generalrelativity101/appendix-c-the-covariant-derivative-of-the-ricci-tensor, and it said that if you take the covariant derivative of a tensor with respect to a superscript, then the partial derivative term has a MINUS sign. How? The...
  26. T

    Meaning of ##\ominus## in Hilbert Spaces

    This should be really easy, but I can't seem to find the answer. What does the symbol ##\ominus## mean in the context of Hilbert spaces? As in "##H \ominus A##" where H is a Hilbert space and A is presumably a subspace or subset of H. I'm guessing it's like the inverse of a direct sum...
  27. ghost313

    Faraday-Neumann Law: minus sign?

    I was wondering why is there a minus sign in the equation: EMF= -d(flux)/dt If this equations is derived from a previous equation which is: EMF= vL•B Why doesent the minus sign just appear in the derivation?
  28. R

    Maple Simplying linear equation to get quartic in q with using Maple and using Descarte’s rule of sign

    Using the maple I am trying to get quardic in q from this big linear equation. Then use Descarte’s rule of signs to determine the number of positive roots. \begin{equation} \frac{\gamma*q*P_Q}{k_p*(1-q)*P_C} =...
  29. 2

    Negative sign when finding forces from derivative of potential?

    Hi! I'm currently reading a book where they give the Coulomb potential, gravitational potential and harmonic potential as +Q1Q2/4∏εx -Gm1m2/x +(1/2)qx2 I think I get the signs as they are used here, but when I am trying to find the force by taking the derivative of these with respect...
  30. F

    Why Are Clockwise Moments Negative and Anti-Clockwise Moments Positive?

    Why are clockwise moments taken as negative and anti-clockwise moment as positive? Why not the other way around?
  31. S

    Plus sign in triangle usage (or minus, times)

    Can anyone refer me to a paper where the "plus sign in triangle", "minus sign in triangle", and/or "multiplication sign in triangle" are used? I'm reading a paper from the 80's where these symbols act on an image ("internal law" and "external law"); however, I'd like to see the symbols applied...
  32. A

    Is the Phase Constant in SHM Conceptually Significant?

    Please look at picture. My textbook only gives the answer with -pi as a phase constant. But, since we are at "a switching point" on the unit circle, the sign doesn't really matter. The graphs give the same result whether a positive or negative sign is used. Am I right? Does it conceptually...
  33. Maxo

    Understanding the Sign of 'g' and 'a': An Apparent Weight Example

    In my physics book the equation for apparent weight is given as FN = mg + ma where FN is the normal force, m is the mass of the object, g is the gravitational acceleration of the object (= 9.8 m/s2) and a is the acceleration of the system. For example the system could be someone standing on a...
  34. X

    Understanding Passive Sign Convention: Power Calculation Example (P=VI)

    Homework Statement I am having trouble understanding PSC. Please help on this question. Teach me like I am 5. My tutor couldn't break it to me. (SEE ATTACHED) and find whether the power is being given or taken Homework Equations p=vi p=-vi The Attempt at a Solution I can't...
  35. 9

    Solving Eigenvectors for Root -7 of 2x3 Matrix

    Homework Statement Find eigenvector for the root -7 of: |2 3| |3 -6| Homework Equations |2 3| |3 -6| The Attempt at a Solution I got 1 -3 But my books says -1 3 I am only wondering if this is possibly the same answer, because when I check my answer by multiplying...
  36. M

    Sign Convention for Work Done by Varying Force

    I am trying to find the work done on a particle when a varying force acts on it. I am familiar with W = ∫F dot ds but am running into a sign question. Suppose a particle is moving in the -x direction because a force is acting on in that direction. Suppose it moves from x = 4 to x = 0, and...
  37. baby_1

    Negative sign in voltage equation

    hello as we know if we wanta find the resistance of a material we use this equation but in electromagnetic course we know that voltage equation has negative sign that it is refer to positive charge thas positive sing and negative charge has negative sing . why in resistance...
  38. J

    AP Question Torque Sign Conventions

    On the 2012 AP Physics C Mechanics test, I got confused by the sign conventions for torques on question 3. (http://apcentral.collegeboard.com/apc/public/repository/2012_frq_physics_cm.pdf) In the scoring guidelines...
  39. Einj

    Doubt on sign of the propagator on Peskin

    Hi everyone. I was trying to reproduce the calculation needed to include the QCD correction to the low energy electroweak Lagrangian. In particular I am looking at Peskin section 18.2. In equation 18.35 an extra minus sign appears on the numerator of the second fermion propagator. Can anyone...
  40. Z

    Sign confusion when taking gradient (Newton's Method)

    I'm watching a lecture on Newton's method with n-dimensions but I am kind of hung up on why the professor did not use the negative sign while taking the first gradient? Is there a rule that explains this or something that I'm forgetting? The rest makes sense but highlighted in red is the part I...
  41. DocZaius

    Constant of integration's sign

    Homework Statement Solve for A: dA/ds = -k s Homework Equations See problem statement The Attempt at a Solution I switched the equation around: dA= -k s ds Integrated: A= -(k/2) (s^2+c) Apparently, that is wrong and I see that the answer should be: A= -(k/2)...
  42. Z

    Sign confusion when taking gradient (Newton's Method)

    I'm watching a lecture on Newton's method with n-dimensions but I am kind of hung up on why the professor did not use the negative sign while taking the first gradient? Is there a rule that explains this or something that I'm forgetting? The rest makes sense but highlighted in red is the part I...
  43. R

    Integrating with Negative Signs: Effects on Solutions

    While working on an integration problem I found that I will arrive at two different solutions depending on how I approach it. I'm finding the arc length of y=ln(1-x2) on the interval [0,0.5] The formula for finding the arc length is ∫sqrt[1+[f'(x)]2]dx So f'(x) = -2x / ( 1-x2 ) Here...
  44. karush

    MHB Integration Sign Error: TI-Nspire Solution

    the bk did not give an answer for this but my TI-nspire gave what is shown, however I don't know where the - sign (see red arrow) comes from. I looked at the steps given in W|A but thot all the substitution was not needed to solve this.
  45. L

    Sign of Hamiltonians: Plotting U & Phase Portraits

    How do you decide on the sign of a Hamiltonian function? For example, I have the following system of differential equations: x'=y y'=-\dfrac{3}{2}x^{2}-2x With the following Hamiltonian: H^{\oplus}=\dfrac{1}{2}x^{3}+x^{2}+\dfrac{1}{2}y^{2} because \dfrac{dH^{\oplus}}{dt}=0. But if...
  46. W

    Differentiation under the integral sign

    I have read about this method , and how feynman utilized this method. I like doing integrals for fun, but I can't seem to understand the conceptual idea on how to introduce a parameter into the integral. Can someone , in detail, explain to me how to introduce the parameter into the integral ...
  47. KodRoute

    How do I determine the sign of this permutation

    Homework Statement Find the sign of the permutation --> Picture here: http://tinypic.com/view.php?pic=2q8rkso&s=5 No other given data. Homework Equations ε(σ) = (-1)^m(σ). If i < j and σ(i) > σ(j) then there's an inversion. Where ε(σ) denotes the sign of the permutation and m(σ) the number of...
  48. R

    When can we move the del operator under an integral sign?

    Homework Statement Hi, it's me again. I'm new to vector calculus so this might sound like a stupid question, but in relation to a specific problem, I was wondering when we could move the del operator under the integration sign - in relation to a specific problem, which is: A(r) = integral...
  49. M

    Understanding the Sign Problem in Electric Potential: A Simple Explanation

    I've been having a problem with the sign of potential. Electric potential as I know it is defined as V = -\int_{C}\vec{E}\bullet\vec{dl} where C is the path from a location defined as zero potential to the location you are measuring the potential at. Now I want to run through this really quick...
  50. 7

    Regarding r and sign convention for Position vectors for moments

    Homework Statement The Attempt at a Solution I'm having trouble understanding how r1 = -1.5j and r2= r3 = 0. Can anyone make this a little clearer for me? I've spent quite a while trying to wrap my head around it but to no avail.
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