# What is Eom: Definition and 38 Discussions

Eom Hye-won (Korean: 엄혜원; born 8 September 1991) is a South Korean badminton player who specializes in doubles. She became national representatives since 2004, and was selected to join the national team in 2008. As a member of Korea National Sport University team, she awarded as the 2011 best player by the Badminton Korea Association.

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1. ### Lagrangian for a rod pivoting at the end of a clock hand

For (d), I am confused how ##a(t)## oscillates harmonically. The EOM is ##ml^2\ddot \phi + mRl\varphi \dot \phi\sin(\phi - \varphi t) = 0## Then using ##\phi - \varphi t = a(t)## ##l\ddot \phi + R\phi \varphi a(t) = 0## Where I used the small angle approximation after substituting in ##a(t)##...
2. ### A How can I use a fiber EOM to lock a laser with a large input power?

I am trying to buy an EOM for a PDH lock with a large laser input power and I was told I should go for a free space EOM. I see that they come as resonant and non-resonant, but I can't seem to understand the advantage of a non-resonant one. The resonant one seems to do pretty much everything the...
3. ### Help with Inverted Pendulum on Cart EoM

Hi All, My goal is to relearn some control theory and implement a working inverted pendulum on a cart with an industrial linear motor. See video: Working through an example of an inverted pendulum on a cart posted here...
4. ### I Understanding the Equations of Motion for the Dirac Lagrangian

I'm having trouble following a proof of what happens when the Dirac Lagrangian is put into the Euler-Lagrange equation. This is the youtube video: and you can skip to 2:56 and pause to see all the math laid out. I understand the bird's eye results of the Dirac Lagrangian having an equation of...
5. ### Constant acceleration in a rocket

I thought I'd start by writing the problem in a tensor formalism. I have identified with ##S## the Earth and ##S'## the rocket. Since the acceleration provided is in the rocket's frame of reference, I can write the following four-vector. $$a'^\mu=(0, a, 0, 0)$$ Since we are interested in the...
6. ### Lagrangian for the electromagnetic field coupled to a scalar field

It is the first time that I am faced with a complex field, I would not want to be wrong about how to solve this type of problem. Usually to solve the equations of motion I apply the Euler Lagrange equations. $$\partial_\mu\frac{\partial L}{\partial \phi/_\mu}-\frac{\partial L}{\partial \phi}=0$$...
7. ### EOM of simple pendulum submerged in a fluid

The question :- My attempt :- The confusion that I am having is that to get the required form of the equation of motion, I had to approximate ##\theta## to be small to get ##x=l\theta## so that I could get the acceleration and the velocity. But, I had to leave the ##sin(\theta)## in the...
8. ### I Quick question for Finding EOM with diff eq

I have been going through my old books again, and found myself a little stuck. I am not entirely sure if this would be better in this one or diffy eq. The problem starts with having you find equation of motions when a= -bv, where b is constant and v = v(t) Using method of separable equations...
9. ### Derivation of EoM for two interconnected rigid bodies

I set a small project for myself to design a controller for a rocket, which moves a mass around to shift the center of mass, in order to steer a rocket. The picture shows a simplified model of a rocket plus a movable mass. , shown is a rod for the rocket, and a mass for the controller. there...
10. ### I EoM via varying action - covariant derivative when integrate

##\int d^4 x \sqrt {g} ... ## if I am given an action like this , were the ##\sqrt{\pm g} ## , sign depending on the signature , is to keep the integral factor invariant, when finding an eom via variation of calculus, often one needs to integrate by parts. When you integrate by parts, with...
11. ### Conformally flat s-t, includes implicit dependence in EoM?

1. Homework Statement Question attached 2. The attempt at a solution Time-like killing vector is associated with energy. ## \frac{d}{ds} (\frac{\mu^2\dot{t}}{R^2})=0## Let me denote this conserved quantity by the constant ##E=\frac{\mu^\dot{t}}{R^2}## where ##\mu=\mu(z)## . similarly we...
12. ### EoM from action, indices confused, (QFT)

Homework Statement Using the E-L equations to get the EoM from the action. Homework Equations I am using E-L equations in the form: ## \frac{\partial}{\partial_u} \frac{\partial L}{\partial_u \phi}-\frac{\partial L}{\partial \phi} ## where ##L ## is the Lagrangian The Attempt at a...
13. ### Electromagnetic Lagrangian, EoM, Polarisation States

Homework Statement Attached: Homework Equations Euler-Lagrange equations to find the EoM The Attempt at a Solution [/B] Solution attached: I follow, up to where the sum over ##\mu## reduces to sum over ##\mu=i## only, why are there no ##\mu=0## terms? I don't understand at all. Many...

16. ### QF, action, EoM, mass of particle, on-shell

Homework Statement Question attached. I am stuck on part d, but give my workings to all parts of the question below. Homework EquationsThe Attempt at a Solution [/B] a) EoM given by E-L equations: Gives ##-\partial_u\partial^u \phi + m^2 \phi - \frac{\lambda \phi^3}{3!} =0 ## b) ## L=T-...
17. ### Quantum Theory: derive EoM of action for a 'general' potential

Homework Statement Action attached: To find the EoM of ##\phi ## / ##\phi^* ## Homework Equations The Attempt at a Solution [/B] Without deriving from first principles, using E-L equations I have: ## \partial_{u}\frac{\partial L}{\partial_u \phi} - \frac{\partial L}{\partial \phi} =0 ##...
18. ### A EoM in Schwarzschild geometry: geodesic v Hamilton formalism

Hi there guys, Currently writing and comparing two separate Mathematica scripts which can be found here and also here. The first one I've slightly modified to suit my needs and the second one is meant to reproduce the same results. Both scripts are attempting to simulate the trajectory of a...
19. ### I What is the expected result of plugging equations of motion into the Lagrangian?

I know that in general plugging the EOM into the Lagrangian is tricky, but it should be perfectly valid if done correctly. Can someone help me see what I'm doing wrong here? I know I'm doing something dumb but I've been staring at it for too long Start with the E&M Lagrangian: L =...
20. ### Question on general solution to harmonic EoM

Homework Statement An equation of motion for a pendulum: (-g/L)sinΦ = Φ(double dot) Homework Equations L = length g = gravity ω = angular velocity Φο = initial Φ The Attempt at a Solution The solution is Φ=Asinωt+Bcosωt solving for A and B by setting Φ and Φ(dot) equal to zero respectively...
21. ### Real scalar field , Action, variation, deriving EoM

## L(x) = L(\phi(x), \partial_{u} \phi (x) ) = -1/2 (m^{2} \phi ^{2}(x) + \partial_{u} \phi(x) \partial^{u} \phi (x))## , the Lagrange density. ## S= \int d^{4}(x) L (x) ##, the action. ## \phi -> \phi + \delta \phi ## (just shortened the notation and dropped the x dependence) I have ##...
22. ### What is the purpose of Electro-Optical Modulator (EOM)?

Hello, I'm studying the setup of distributed Brillouin sensor (using fibre optics) and don't quite understand the purpose of EOM in the sensor. It says that "to generate both the pump and the probe waves from a single physical light source by using an electro-optical modulator (EOM)", but since...
23. ### I Evolution style algorithm to determine EOM

I had seen a documentary about an algorithm that uses notions of evolution to deduce the equation of motion of a system by sampling a variable connected with the system. For example, they used the double pendulum case where they sampled the position of the free end of the pendulum and arrived...
24. ### Hamilton EOM for Schwarzschild Metric: Problem Solved

I have a problem (this is not homework) Based on covariant Lagrangian ## \mathcal {L} = \frac {m}{2} \frac{dx^{\mu}}{ds} \frac {dx _ {\mu}}{ds} ## record the equations of motion in Hamiltonian form for a particle in the Schwarzschild metric (SM). Based on Legandre transformations...
25. ### Rotational EOM's with non diagonal inertia tensor

I'm having difficulties understanding how I should calculate the angular velocities of a rigid body when the inertia tensor is given in body coordinates and has off diagonal elements. Let's assume I have an inertia tensor ## I = \begin{bmatrix} I_{xx} & -I_{xy} & -I_{xz} \\ -I_{yx} &...
26. ### Lagrange EOM for 2 masses on a string

Homework Statement Derive the equation of motion for the system in figure 6.4 using Lagrange's equations [/B] Homework Equations m1=.5m m2=m strings are massless and in constant tension Lagrange=T-V The Attempt at a Solution I currently have the kinetic energy as .5m1y'12 + .5m2y'22 I am...
27. ### EOM for Pendulum hanging from spring

Homework Statement Derive Newton's and Lagrange's equation of motion for the system. Discuss differences and show how Newton's equations can be reduced to lagrange's equations. Assume arbitrarily large θ. The system is a pendulum consisting of a massless rod of length L with a mass m...
28. ### Euler-Lagrange equation (EOM) solutions - hairy lagrangian

I'm going through Zwiebach Chapter 6 on relativistic strings to try to solve a similar problem. I got all the way to my equation of motion \begin{eqnarray*} \delta S & = & [ p' \delta \theta]_{z 0}^{z 1} + \int_{z 0}^{z 1} d z \left( p - \frac{\partial ( p')}{\partial z} \right) \delta...
29. ### Scalar field in Expanding Universe EOM

I would like to ask something. How is the solution of EOM for the action (for FRW metric): S= \int d^{4}x \sqrt{-g} [ (\partial _{\mu} \phi)^{2} - V(\phi) ] give solution of: \ddot{\phi} + 3H \dot{\phi} + V'(\phi) =0 I don't in fact understand how the 2nd term appears... it...
30. ### EoM for rigid body, wrench and twist help

I am currently working on a robotic manipulation problem and need to form a model for how an object responds. I start by writing up the equations of motion for the body, the motion is then constrained by an additional constraint equation. However, I am new to the notions of twists and wrenches...
31. ### Can I Use the EOM to Simplify an Interaction Term in Feynman Diagrams?

Hi, I am given an interaction lagrangian piece as \mathcal{L}_1 = \frac{1}{2} g \phi \partial^\mu \phi \partial_\mu \phi Now normally when I have an interaction lagrangian piece I turn the field's into variations with respect to the source \delta_J, and take variations of the free partition...
32. ### Non-radiative density matrix EOM

Dear all, Could anyone please explain to me for a 3 level syste, coupled with 2 lasers, what is the equation describing the disspative term of the equation of motion of the density matrix? I am looking for a non-radiative decay, namely the overall population should conserved. I have found...
33. ### How to find the transfer function (frequency response function) given the EOM

for a given spring/damper system the equation of motion is: [PLAIN]http://img600.imageshack.us/img600/2140/equation1.png where x is the displacement of a mass from a fixed point d is a damping constant L1 and L2 constant lengths k1 and k2 are 2 spring constants...
34. ### Deriving EOM of cantilever beam using specific Lagrangian

Homework Statement The specific Lagrangian for a cantilever beam is given by: \overline{L}=\frac{1}{2}m[\dot{u}^2(s,t)+\dot{v}^2(s,t)]-\frac{1}{2}EI[\psi ^{\prime}(s,t)]^2 where m,EI are mass and bending stifness, respectively. \dot{u},\dot{v} are velocities in u,v directions...
35. ### Pulley system with spring and car EOM

Hi all! I am working with a problem that for the life of me am having the hardest time with deriving the equation of motion. I have attached the sketch to give a better representation. The moment of inertia, J, is at the center of the spring. No friction between car and table and cables do...
36. ### Deriving EOM to Describe Wheelie Motion of a Car

Homework Statement Equations of motion are to be derived to describe the motion of a car(rear wheel drive) at rest which then accelerates to perform a wheelie. Basically, I need equations of motion that would help me determine the force that the rear wheels exert on the car in order to...
37. ### Why no EOM in QFT with higher than second order derivatives in time and space?

When we write down a Lagragian for a quantum field theory, it is said that it should not depend on the second and higher order time and space derivatives of \phi, because we want the equation of motion(EOM) to be at most second order. Why is it so important. What trouble will a higher order EOM...
38. ### Deriving the EOM for Proca Lagrangian

Homework Statement Consider the Proca Lagrangian L=-\frac{1}{16\pi}F^2-\frac{1}{c}J_{\mu}A^{\mu}+\frac{M^2}{8\pi}A_{\mu}A^{\mu} in the Lorentz gauge \partial_{\mu}A^{\mu}=0 Find the equation of motion. Homework Equations F^2=F_{\mu\nu}F^{\mu\nu} The Attempt at a...