Sign Definition and 596 Threads

I was reading through hobson and my notes where the covariant acts on contravariant and covariant tensors as \nabla_\alpha V^\mu = \partial_\alpha V^\mu + \Gamma^\mu_{\alpha \gamma} V^\gamma \nabla_\alpha V_\mu = \partial_\alpha V_\mu - \Gamma^\gamma_{\alpha \mu} V_\gamma Why is there a minus...

Homework Statement I'm trying to figure out why potential energy decreases in this situation http://imgur.com/9PfjRVE Homework Equations ΔU = FΔy The Attempt at a Solution If I define up to be positive, and ΔU = FΔy. In this picture, force is pointing down (so it is negative) and the height...

Comparing two sources one has ##\frac{d^{2}x^{i}}{dt^{2}}=-\frac{1}{2}\epsilon\bigtriangledown_{i}h_{00} ## and the other has ##\frac{d^{2}d^{i}}{dt^{2}}=\frac{1}{2}\epsilon\bigtriangledown^{i}h^{00}##, And the one using the lower index has the Newton-Poisson equation as ##...

In physics book, if work is done by the system, it is positive in my chemistry book, if work is done by the system, it is taken as negetive. when I asked my chemistry teacher, he said the sign convention is different in physics and chemistry. but why are they different?

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...

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...

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

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...

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...

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...

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...

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...

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...

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.

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...

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...

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...

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...

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!

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!

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...

why there is a negative sign in the tensor moment of inertia??

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.

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...

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?

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...

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)...

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...

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...

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...

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?

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} =...

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...

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

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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)...

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...

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...

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.

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...

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 ...