# Questions tagged [conventions]

A convention is a set of agreed, stipulated, or generally accepted norms. It typically helps common efficiency or understanding but is not required, as opposed to a strict standard or protocol.

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### Is force always the negative change in potential energy with respect to position?

For example, In the non-inertial rotating reference frame of a turntable that has a tether ball pole rotating on top of it, the ball at the end instantly starts rotating and then eventually moves up ...
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### Ordering of Tensor indices: a specific example

As an example of construcing tensors out of the product of other tensors I found the following example. $$T_{i}{}^j{}_{kl}=A_i{}^jB_{kl}+C_m{}^{mj}D_{ikl}$$ But I am a bit confused about the ...
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### If velocity in forward and backward directions is positive and negative respectively, then what is it in left and right directions? [closed]

I have defined velocity in forward direction to be positive and negative in the backward direction. So what is the velocity if the body is moving right or left?
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### Why do (kilo)watt-hours double-count units per time?

A watt is defined as 1 joule per second and is therefore a measurement of energy transfer over a period of time. A kilowatt-hour is a measurement of energy equal to one kilowatt sustained over a ...
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### How can we apply lens makers formula to combination of lenses?

Like in lens makers formula the material must have same material on both sides but that doesnt happen when lenses are touching each other. So how can we neglect that connection and use formula as if ...
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### What is wrong with this calculation of work done by an agent bringing a unit mass from infinity into a gravitational field? [duplicate]

Let us assume that a gravitational field is created by a mass $M$. An agent is bringing a unit mass from $\infty$ to distance $r < \infty$, both measured from mass $M$. The agent is always forcing ...
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### Why is the gravitational potential energy defined as negative? [duplicate]

It is said that since work is done by the gravitational potential itself , so at a finite distance the gravitational potential energy of the body is negative. Could someone explain why?
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### Problem with Cartesian sign convention for geometrical optics [duplicate]

This confuses me a lot. We use the convention in the derivation of thin lens formula and mirror formula. In derivation in place of u (object distance) we write -u. Since we have written it this way, ...
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### Why are these quantization forms different?

I'm confused about the form of the quantized electromagnetic field. Sometimes, one writes the quantized electric field as $$\hat E = \vec E_0(\hat a + \hat a^†)$$ , which can been seen the website ...
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### How can electric flux be negative?

If electric flux is the number of field lines, then how can it be negative?
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### Does the quadratic mass term $\phi^2$ belong to the free Lagrangian or is it an interaction term?

$$L = -\frac{1}{2}\partial_\mu\phi\partial^\mu\phi - \frac{m^2}{2}\phi^2.$$ Why is the $\phi^2$ term in the scalar Lagrangian not considered a self-interaction?
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### Sign of work against an electrostatic field

I think I'm slightly confused with the signs. The work needed in order to bring point charges $q_i$ from infinity to a distance $r$ from some shape of charge $Q(r)$ with a varying charge (because we ...
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### Can we assume a force to already be negative before knowing the value of it? [closed]

Let me make my question clear by the following example:- Let’s take a case of an individual who is in an elevator accelerating downward with some acceleration ‘ a ‘ such that ‘a’ < g . Let’s take ...
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### Regarding sign of energy stored in springs

A block of mass $m$ is at natural length initially.It is attached to two springs having spring constant $k1$ and $k2$. It is attached in such a way that when one elongates ,the other compresses.Using ...
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### Regarding the signs in the Clebsch-Gordan coefficients

Let's take, for example, the $\frac{1}{2}$ $\frac{1}{2}$ spin case. We have, for $J = 1, M = 0$ $$|1,0\rangle=\frac{1}{\sqrt{2}}(|-1 / 2,1 / 2\rangle+|1 / 2,-1 / 2\rangle),$$ and, if we follow the ...
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### Euler beam equation sign confusion

Euler beam equation is defined as follows: $$M=-EI{\frac {d^{2}w}{dx^{2}}}$$ There is a negative sign, so if the second derivative of the deflection is negative, the moment is positive. When the ...
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### Can an affine first-order polynomial system be chaotic?

While studying chaos theory, one of the basic principles presented to me was that chaos only occurs in deterministic nonlinear systems. This pointed me to learn more about the differences between ...
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### Which way of integrating the quaternion representation of orientation is correct?

I am wondering how to integrate a measurement of angular velocity into an orientation quaternion. Suppose I have measurements of the rotation rate about the three principal axes of a body. I would ...
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### If Gravitational potential energy increase with height then why it is 0 at infinity?

Due to MGH relation, if we increase height then potential energy increases. Then why it is zero at infinity?
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### Sign convention for Maxwell's model of viscoelastic material

Maxwell's equation for viscoelastic body is $\dot{\varepsilon}(t)=\frac{\dot{\sigma}}{E}(t)+\frac{\sigma}{\eta}(t)$, where $\varepsilon=\frac{dl}{l}$ is strain and $\sigma$ is stress. I am a little ...
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### Conservative Force and Energy [closed]

When a charge is moved from infinity to $r$, its electric potential energy is equal to the negative work done by the field. In this argument, is it also true that there is positive work done by the ...
To my knowledge Work is defined as $W=-\int{\vec{F}\cdot d\vec{s}}$, or in the context of vectorfields as $F=-q\nabla\Phi$ ($q=m$ in the case of gravity). Recently I have been wondering whether there ...