# What is Derive: Definition and 620 Discussions

The dérive (French: [de.ʁiv], "drift") is a revolutionary strategy originally put forward in the "Theory of the Dérive" (1956) by Guy Debord, a member at the time of the Letterist International. Debord defines the dérive as "a mode of experimental behavior linked to the conditions of urban society: a technique of rapid passage through varied ambiances." It is an unplanned journey through a landscape, usually urban, in which participants drop their everyday relations and "let themselves be drawn by the attractions of the terrain and the encounters they find there". Though solo dérives are possible, Debord indicates that the most fruitful numerical arrangement consists of several small groups of two or three people who have reached the same level of awareness, since cross-checking these different groups' impressions makes it possible to arrive at more objective conclusions.The dérive's goals include studying the terrain of the city (psychogeography) and emotional disorientation, both of which lead to the potential creation of Situations.

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1. ### Engineering Derive the governing equation for the voltage Vc across the capacitor

I was thinking about doing KVL around the circuit at the right but I noticed when the switch opens, the current through the circuit at the right is not the same throughout -5 + Ic*2*1-^3 + Ic*10^3 = -Vc Ic is not the same around the right circuit so I am stuck....
2. ### A How to derive Quantum Mechanics in curved physical space?

I am following [this YouTube lecture by Schuller][1] where he finds the appropriate formalism for the quantum mechanics in the physical curved space. Everything makes sense to me but at the very end I see that we find the pull backed connection one-form on the base manifold. He says to the end...
3. ### Chemistry Derive an expression for mean free path from survival eqn exp(-x/λ)

If the distance between the centres of two molecules is σ, then imagining a a cylinder with radius σ the number of molecules can be given by πσ²cn where c = average velocity. So mean free path can be given by λ = c/πσ²cn = 1/nπσ². But do I derive it from exp(-x/λ)?
4. ### Derive an expression for the radial charge distribution of an E field

I know we're supposed to attempt a solution but I'm honestly super confused here. I think the second an third terms of the del equation can be cancelled out because there is only an E field in the r hat direction, so no e field in the theta and phi directions. That leaves us with ##\nabla \cdot...
5. ### I Need to resort to spherical wavefront to derive the LTs?

I have been reading Wikipedia’s derivations of the Lorentz Transformations. Many of them start with the equation of a spherical wavefront and this reasoning: - We are asked to imagine two events: light is emitted at 1 and absorbed somewhere else at 2. For a given reference frame, the distance...
6. ### Derive angular frequency for mass spring system

tried writing the x position as x = Acos(wt) (ignoring the phase) so that d2x / dt2 = -w2x Substituting that into the individual motion equations would get the required result for the individual masses, but I am not sure how to combine the equations to get the reduced mass
7. ### A How do we derive the number of string excitation modes for large N?

On page 52 in Becker, Becker, Schwarz, there is an equation (2.148) for the number of open string excitation modes. I tried to Tayler expand eq 2.145, but couldn't reproduce 2.148. Plus, one gets 2.145 by setting w close to 1; even if I use the 2.146 and try to analyze it around 0, I am still...
8. ### I How can I derive this relation from Snell's law?

Here, it's shown how white light, after passing from air to another medium, gets broken down into its constituent coloured rays. Each has its own refractive index in the medium, but it's only shown here red, blue and yellow. The auther comments on this image and says that, for small angles of...
9. ### Derive ## a^{7}\equiv a\pmod {42} ## for all ## a ##

Proof: Observe that ## 42=6\cdot 7=2\cdot 3\cdot 7 ##. Applying the Fermat's theorem produces: ## a\equiv 1\pmod {2}, a^{2}\equiv 1\pmod {3} ## and ## a^{6}\equiv 1\pmod {7} ##. Thus \begin{align*} &a\equiv 1\pmod {2}\implies a^{6}\equiv 1\pmod {2}\implies a^{7}\equiv a\pmod {2}\\...
10. ### Derive the following congruence....

Proof: Observe that ## 15=3\cdot 5 ##. Applying the Fermat's theorem produces: ## a^{3}\equiv a\pmod {3} ## and ## a^{5}\equiv a\pmod {5} ##. Thus \begin{align*} &(a^{3})^{7}\equiv a^{7}\pmod {3}\implies a^{21}\equiv [(a^{3})^{2}\cdot a]\pmod {3}\implies a^{21}\equiv a\pmod {3}\\...
11. ### How Do You Derive the Klein-Gordon Propagator from Commutation Relations?

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12. ### MHB How to Derive Answers Using N Formula

Hi, I have been given the attachment formula and asked to enter this into an excel spreadsheet. Although I am not entirely sure how the answer was derived. Is anyone able to explain step by step as I want to try and enter this into an excel spreadsheet. For reference N = Newtons
13. ### Derive the Venturi Meter eqn from the Bernoulli eqn

Advanced apologies for this format; I am posting my question as an the image b/c the Latex is being very buggy with me, and I lost a kind of lengthy post to it. Can anyone show me what I am doing wrong? I have attached a pdf version for easier reading if need be.
14. ### A How to derive the sampling distribution of some statistics

Assume that ##T## has an Erlang distribution: $$\displaystyle f \left(t \, | \, k \right)=\frac{\lambda ^{k }~t ^{k -1}~e^{-\lambda ~t }}{\left(k -1\right)!}$$ and ##K## has a geometric distribution $$\displaystyle P \left( K=k \right) \, = \, \left( 1-p \right) ^{k-1}p$$ Then the compound...
15. ### I Using Dimensional Analysis to derive an equation (Walter Lewin video)

Hello everyone. I was watching the Walter Lewin lectures and I noticed in the talk he used something called dimension analysis to study the time it takes for an object to drop based on differing heights. I'm 22:07 minutes into the video. With some guess work on what's proportional to what...
16. ### Integrating motion equation to derive displacement

##\frac{dx}{dt} = \frac{dx_i}{dt} + \frac{d^2x}{dt^2}t## Multiplying dt on both sides and integrating we have ##\int_{x_f}^{x_i} dx = \int_{0}^{v_i t} dx_i + \int_{0}^{at} dvt## so ##x_f - x_i = v_it + at^2##, which is not right Where did I go wrong? I understand that if we substitute a for...
17. ### I Derive the probability of spin at arbitrary angle is cos( )

From Dr. Leonard Susskind's Stanford Lecture: Quantum Entanglement, Lecture 4, he sets up a "given particle is spin up along n (arbitrary direction) and discusses : what is probability we measure up along another arbitrary m directionHe does all of the setup, - calculates the eigenvectors and...
18. ### I How to 'reverse' derive correct value when given MEAN + SD

I have a scatterplot that I'm trying to extract. I found 54 values out of 55. There is one "missing" value, probably because it is overlapped and I can't actually see. I have the MEAN and Stand Dev of the 55 values. Is there a way to reverse find the one that is missing? I mean, is there a...
19. ### I Trying to derive Gauss' law using a cylindrical surface

When I try to derive Gauss's law with a straight line of charge with density ##\lambda## through a cylindrical surface of length L and radius R, $$\vec E = \frac{\lambda*L}{4\pi\epsilon*r^2}$$ $$A = 2\pi*r*L$$ $$\vec E*A = \frac{\lambda *L^2}{2\epsilon*r} \neq \frac{q_{enc}}{\epsilon}$$ What am...
20. ### I Open channel flow: derive function for energy slope on friction?

I want to determine the normal flow depth in a perfectly horizontal circular conduit. The system characteristics are known (Internal pipe diameter, Mannings roughness, Discharge). However, I am not sure how to calculate the normal flow depth. When using Manning's equation one can find the normal...
21. ### Derive ##\dfrac{\rho_1}{\rho_2}=\dfrac{T_2}{T_1}##

I just found here(https://byjus.com/physics/relation-between-density-and-temperature/#:~:text=Density and Temperature Relationship 1 When density increases,,reduces. 4 When the temperature decrease, density increases.) that P=##rho##RT. So they just took ##\rho=\frac{n}{V}##...
22. ### Derive an upper bound for |f(i)|

##\mathbb{D}## is open. Let ##\mathbb{A}:=\{z:|z-i/2|=\frac{1}{9}\}##. ##\mathbb{A}## is closed and contained in ##\mathbb{D}##. ##f## is analytic in ##\mathbb{D}##, so ##f## is analytic on the interior to and on ##\mathbb{A}##. By the Cauchy integral formula, ##f^{(4)}## exists at every point...
23. ### B How to derive the Lorentz transformation in the simplest way?

Is there the simplest, direct, and easy-to-understand method that only needs to apply the most basic algebra and logic to completely and strictly derive the Lorentz transformation? Thanks for your help.
24. ### I How Can One Derive the Diffraction Pattern Formula from a 1D Aperture?

I've been trying to derive a formula for diffraction pattern formed by casting a plane-wave through a generic 1D aperture onto a screen distanced ##L## from the aperture. The aperture is described by an opacity function ##f:\mathbb{R} \rightarrow [0,1]## so it can be a single slit, multiple...
25. ### A How to derive the Momentum and Energy Operators from first principles?

So we all know that the form of the momentum operator is: iħd/dx. And for energy it is iħd/dt. But how do we derive these operators? The only derivations of the i have seen is where the schrødinger equation was used, but that makes the logic circular, because the Schrødinger-Equation is derived...
26. ### I How to derive Schrodinger's equation?

Homework Statement:: Derive Schrodinger equation Relevant Equations:: Schrodinger Equation I want to find the derivation of Schrodinger Equation. Actually, I learned quantum mechanics already, but I think the proof that begins from the plane wave solution is quit ambiguous. Because I feel...
27. ### B Derive Special Relativity: Alternative Paths

The only way I know of to derive special relativity is to start with the two postulates, derive the Lorentz transformations, and rewrite the laws of physics consistent with those transformations. Are there alternative ways to derive special relativity? Thank you.
28. ### Using Lorentz Force to derive V = E/B

Suppose the E-field is ##-E_y\hat y##, and B-field is ##B\hat z##. Mass is ##m##. z | |_____x / y ##m(\ddot x \hat x + \ddot y \hat y) = q(-E_y \hat y + (v_x \hat x + v_y \hat y) \times B \hat z)## By grouping terms with ##\hat x## and ##\hat y## together, ##m\ddot x = -qv_yB##...
29. E

### I To derive an equation of black hole thermodynamics

This is the problem statement: We can start by writing ## (\star d \star d \xi)_a = - \nabla^b (d\xi)_{ab} = - \nabla^b \nabla_a \xi_b + \nabla^b \nabla_b \xi_a = 2\nabla^b \nabla_b \xi_a ##. Then with ##\nabla_a \nabla_b \xi_c = R_{cbad} \xi^d = -R_{bcad} \xi^d## we can contract over...
30. ### Derive the period of a Ball rolling in a Bowl

The following attempt gives the wrong answer, and I would like to know where it goes wrong. Let ##\theta## be the angle of the ball with the vertical passing through the centre of the bowl, and ##\phi## be the angle the ball rolls through. Let ##m## be the mass of the ball, ##r## be the radius...
31. ### Derive the Maxwell "with source" equation

We need to derive the Maxwell "with source" equation, of course, using the tensor equation $$\partial F^{\mu v}/ \partial x^{v} = j^{\mu}/c$$ D is the spacetime dimension To do this, it was said to us vary the action wrt the ##A^{\mu}## The first term just vanish, and I want to evaluate the...
32. E

37. ### How do you derive the units for momentum for photons

So if i have a photon of some energy and i want to find the magnitude of the momentum, i can get the right answer but the units don't make sense. So i derive p = E/c since i know the energy of the photon and i used f=E/h and substituted this into p=hf/c This means for units of the equation p...
38. ### I Derive local truncation error for the Improved Euler Method

I'm trying to find the local truncation error of the autonomous ODE: fx/ft = f(x). I know that the error is |x(t1) − x1|, but I can't successfully figure out the Taylor expansion to get to the answer, which I believe is O(h^3). Any help would be greatly appreciated!
39. ### Rearranging gravitational and centripetal equations to derive formulas

1. Newton's Second Law states F=ma and the formula for centripetal acceleration is v^2/r Therefore, F= mv^2/r Would this be complete, I just feel that I should need to do something further but I am not sure what? 2.F=mv^2/r Gravitational force = GMm/r^2 Gravity is the cause of centripetal...
40. ### Derive a general expression for the dilution of saltwater

I know that it will take 3 washings to reach the desired purity of sand, and that "N-1" is an exponent in the general expression, but I am stuck beyond that.
41. ### How do I derive this vector calculus identity?

##(\nabla\times\vec B) \times \vec B=\nabla \cdot (\vec B\vec B -\frac 1 2B^2\mathcal I)-(\nabla \cdot \vec B)\vec B## ##\mathcal I## is the unit tensor
42. ### How to derive this thermodynamic math identity

So the Legendre transforms are straightforward; define ##S_1=S-\beta E## and ##S_2= S-\beta E + \beta \mu n## then we get: ##dS_1 = -Ed\beta - \beta \mu dn + \beta PdV## ##dS_2 = -Ed\beta + nd(\beta \mu) + \beta PdV## And so by applying the equality of mixed partials of ##S_1## and ##S_2## we...
43. ### I Deriving Lorentz Transformations Using Calculus

We take an arbitrary spacetime point ##(x,t)## in any observer's reference frame ##A##. Let ##(x(v),t(v))## be the co-ordinates of this same event as seen from a frame ##B## moving at a velocity ##v## wrt ##A##. As ##v## varies, the set of points ##(x(v),t(v))## constitute some curve ##C##. So...
44. ### Derive Newtonian gravity from symmetry?

Is it possible to derive laws of Newtonian gravity from some symmetries?
45. ### A Derive the Principle of Least Action from the Path Integral?

Several weeks ago I had considered the question as to how one can start from the Schroedinger Equation, and after several transformations, derive F=ma as a limiting case. At some point in my investigations of this derivation, it occurred to me that this is simply too much work. While in...
46. ### I Understanding how to derive the relativistic-relative velocity formula

I was studying how to derive the cross-section formula in the CoM frame from Mandl & Shaw QFT's book, and they state the following formula for the relative velocity (I'm going to use Vanhees71's notation though) $$\omega_1 \omega_2 v_{rel} = [(p_1 p_2)^2 - m_1^2 m_2^2]^{1/2} \ \ \ \ (2)$$ Then...
47. ### How to derive the reflected Mach number relationship?

Hi, when learnig about reflected waves, I keep coming up with this equation; to calculate the reflected mach number (Mr). I can't seem to find the derivation for this and would appreciate your help Thank you
48. ### I Understanding how to derive the cross-section formula in the CoM frame

We work in natural units. Let's assume in this post that the differential cross-section of two particles that, after collision, yield ##N## particles is given by the following formula: d \sigma = (2\pi)^4 \delta^{(4)} (\sum p'_f - \sum p_i) \frac{1}{4 E_1 E_2 v_{rel}} \Pi_l (2m_l) \Pi_f...
49. ### A Understanding how to derive the differential cross-section formula

Please let me make questions after showing what I am studying. We first consider two particles (they may be either leptons or photons) with initial (i.e. before collision) four momentum ##p_i = (E_i, \mathbf p_i)##, ##i=1,2##. These two collide and produce ##N## final particles with momentum...
50. ### How to derive Eq. (4.26) from Eq. (4.25) in Birger Bergersen's book (Maier-Saupe model)

The dictators at physics.stackexchange want to close my post that I post here. I hope someone can help me with this question, I want to compute this by hand, without Computer algebra software, mainly because I don't know which syntax to use for Mathematica (if you know the syntax, can you give...