deriving Definition and 1000 Threads

SI derived units are units of measurement derived from the
seven base units specified by the International System of Units (SI). They can be expressed as a product (or ratio) of one or more of the base units, possibly scaled by an appropriate power of exponentiation (see: Buckingham π theorem). Some are dimensionless, as when the units cancel out in ratios of like quantities.
The SI has special names for 22 of these derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m2), the SI derived unit of area; and the kilogram per cubic metre (kg/m3 or kg⋅m−3), the SI derived unit of density.
The names of SI derived units, when written in full, are always in lowercase. However, the symbols for units named after persons are written with an uppercase initial letter. For example, the symbol for hertz is "Hz", while the symbol for metre is "m".

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  1. J

    Deriving EM energy and momentum with noether's theorem

    I think I know how to derive conserved energy and momentum currents of a free EM field. Lagrangian is \mathcal{L}=-\frac{1}{4}F_{\mu\nu}F^{\mu\nu} I then substitute x^\mu\mapsto x^\mu + \lambda u^\mu, and take the derivative in respect to lambda. With some trickery I've got \partial_\mu...
  2. C

    Deriving equation for force from pressure that varies with water level

    Homework Statement Water is filled to a height H behind a dam of width w. Determine the resultant force exerted by the water on the dam. Homework Equations P=pgh = pg(H-y) (where p is density, greek rho) dF = PdA = pg(H-y)wdy (where dA is a narrow horizontal strip of the dam with...
  3. F

    Deriving Molar Specific Heat Equation

    Homework Statement n_1 moles of a monatomic gas and n_2 moles of a diatomic gas are mixed together in a container. Derive an expression for the molar specific heat at constant volume of the mixture. My answer can only use the variables n_1 and n_2, and I'm assuming constants. Homework...
  4. M

    Deriving an Equation from a graph

    Homework Statement Hello everyone, I'm in need of some assistance in regards to deriving an equation from a graph. I have been tasked to graph information which I've collected through experimentation and then write an equation to represent the graph. I'm stuck at steps 3 and 4 and I am not...
  5. R

    Deriving inverse tans from complex product?

    I am supposed to derive 4\,\arctan \left( 1/5 \right) -\arctan \left( {\frac {1}{239}} \right) from the complex product of \left( 1+i \right) \left( 5-i \right) ^{4} I do see how the argument of product of the complex expression is equal to pi/4 - 4 arctan(1/5) but I am totally lost. SO how...
  6. K

    Deriving the Mass of Xi Baryon from Quark Interactions?

    Homework Statement I am trying to derive the mass of \Xi using the formula: M\left(baryon\right)=m_1 + m_2 + m_3 + A' \left[\frac{S_1 \cdot S_2}{m_1 m_2} +\frac{S_1 \cdot S_3}{m_1 m_3} + \frac{S_2 \cdot S_3}{m_2 m_2\3}\right] Homework Equations We have: S_1 \cdot S_2 + S_1 \cdot S_3 +...
  7. E

    Deriving the Bateman equation of Nuclear Decay Chains

    Homework Statement Derive Bateman equation for a decay chain a->b->c->d where each decays with a given mean life let decay constant be L, where L=1/mean life Na(0)=No, Nb(0)=Nc(0)=Nd(0)=0 Homework Equations Want to derive Nb(t)={(No)(La)/(Lb-La)}*{exp[-La*t]-exp[-Lb*t]} extend for...
  8. B

    Deriving Mass Distribution & Rotation Curve Function

    Hello everyone... can someone help me with this problem please: The rotation curve V(r) for a mass distribution characterizes the rotational velocity of a test particle in orbit in its gravitational field as a function of radius from its center. Suppose you have a spherically symmetric mass...
  9. B

    Deriving probability distributions

    Suppose I had a random variable, X, that followed a Gamma distribution. A Gamma distribution can be defined as \Gamma(\alpha,\beta) , where \alpha and \beta are the 'scale' and 'shape' parameters. Now suppose if \alpha was a random variable, say following a binomial distribution, how would...
  10. E

    Deriving B(r) from Ampere's law - For tomorrow (02/23)

    Hello again everyone Part of a problem I've been set is to show that the equation: B(r) = \frac{1}{2}\mu_0 (J x r) from Ampere's law: \nabla x B = \mu_0 J. The problem presents no... uh... problem thereafter, but I'm at a loss where to begin. I've been playing around with random...
  11. V

    Deriving the critical radius of Uranium using diffusion equation

    Homework Statement I have solved the equation for the neutron density as a function of position and time. I need the boundary conditions to change my infinite number of solutions (the varying separation constant) into one value so that my answer for the critical radius does not contain a...
  12. S

    Deriving the Planck Length, Time, and Mass

    How are the Planck length, Planck time, and Planck mass "derived"? I know their values, but I don't understand where we get them from.
  13. Q

    Deriving a balanced bridge equation

    I am having trouble finishing this problem. I am supposed to first derive an equation for V_5 in this circuit: http://img292.imageshack.us/img292/599/picture3qy2.png I applied a Delta-Wye transformation to get here: http://img292.imageshack.us/img292/9672/workot8.jpg From there I am...
  14. S

    How Is the Weyl Tensor Derived?

    Could someone show me a derivation of the Weyl tensor or link me to a good site?
  15. T

    How can we show the equivalence between Biot-Savart law and Ampere's law?

    I am curious how you derive this law. It seems that you could derive coulomb ` s law from gauss ` s law, but are there are no similar analogy for Bio-Savart law.
  16. U

    Deriving heat capacity using thermodynamics identity

    Homework Statement Use the thermodynamic identity to derive the heat capacity formula C_V=T\frac{\partial{S}}{\partial{T}}_VHomework Equations C_V=\frac{\partial{U}}{\partial{T}} T=\frac{\partial{U}}{\partial{S}} dU=TdS-PdV+\mudN The Attempt at a Solution I used...
  17. K

    Deriving Quadratic Equation from Taylor Expansion: An Exercise

    Homework Statement I have the following question to answer: Show that (X^2/h^2)*((1/2*y1) - y2 + (1/2*y3)) + (X/h)*((-1/2 y1)+(1/2 y3))+y2 (sorry about the format) is equal to (taylor expansion): y = y2+(x(dy/dx)¦0 + (x^2/2*((d^2)y)/(dx^2))¦0 Homework Equations also given in...
  18. T

    Deriving Moment of Inertia for a Uniform Rod Rotating about a Non-Center Axis

    Homework Statement A uniform rod of mass M and length L is free to rotate about a horizontal axis perpendicular to the rod and through one end. A) Find the period of oscillation for small angular displacements. B) Find the period if the axis is a distance x from the center of massHomework...
  19. A

    Can Lorentz Transformation Explain Magnetism and the Lorentz Force?

    I read somewhere that the whole of magnetism, and in particular the lorentz force, can be found merely by applying the lorentz transformation to transform the coordinates of the electric field of a charged particle from the frame in which the particle is at rest to a frame in which the particle...
  20. Q

    How is Vmax Derived as 2πfA from Given Formulae?

    Given the following formulaes prove that maximum speed (Vmax) of a mass on a spring is given by 2(pi)(frequency)(Amplitude) (constant k) A^2 = mv^2 + (constant k) x^2 ma = -(constant k)(x) f = 1/2(pi) sqrt (a/-x) and f = 1/2(pi) sqrt (constant k/m) i just don't...
  21. S

    Deriving Electric Field in y-direction from Line Charge of Lambda=4.5 nC/m

    A line charge of liner charge density lambda=4.5 nC/m lies on the x-axis and extends from x=-5cm to x=5cm. Derive an expression for E_y. I have started with this question and it seems that I have to sum the electric fields in the y direction caused by each dx along the line with a charge dq...
  22. M

    Deriving laplacian in spherical coordinates

    Hey... Could someone help me out with deriving the LaPlacian in spherical coordinates? I tried using the chain rule but it just isn't working out well.. any sort of hint would be appriciated. :) \nabla^2 = \frac{1}{r^2} [ \frac{\partial}{\partial r} ( r^2 \frac{\partial}{\partial r} ) +...
  23. U

    Mastering Equation Derivation: Tips for Overcoming Difficulty in Proofs

    I'm in third year undergraduate physics, and more and more I'm seeing problems in homework and assignments that say "Prove that" and "Show that", basically just deriving equations. There's just one problem, I can't do it for the life of me. I had a thermodynamics test recently, and despite...
  24. M

    How Do You Derive the Work Formula for a Mass Moving Against Gravity?

    A body of mass m is in a gravitational field of strength g. The body is moved through a distance h at constant speed v in the opposite direction to the field. Derive an expression in terms of m, h and h, for the work done on the body. Im bad with derivations, I need to get better. So...
  25. E

    How Do You Derive the Geometric Series for 1/(1-x)?

    I could use some help with this question: Derive the geometric series representation of 1/(1-x) by finding a0, a1, a2,... such that (1-x)(a0+a1x+a2x^2+a3X^3+...)=1 Thank you.
  26. A

    Find Expression for Acceleration of Figure w/ Frictionless Table

    So the problem I am working on is: In the figure, find an expression for the acceleration of (assume that the table is frictionless). I have attached the figure of reference. I have so far tried to solve by first looking at m2 to get: 2T-m_2*g=m_2*a so T= (m_2*(a+g))/2...
  27. K

    How Do You Derive the Integral of 1/(x^2 + a^2)?

    Yeah this one is good... Derive the following: int(1/(x^2 + a^2)dx = 1/a*arctan(x/a) + C any idea how I would derive this thing? Cause I'm totally lost...
  28. B

    How can I eliminate phi and u to derive the Compton effect equation?

    Hi everyone, Right now, I am working on a homework problem asking me to derive the Compton effect, which is given by \lambda\prime-\lambda=\frac{h}{m_ec}(1-cos\theta) A diagram of the situation can be found here: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/compton.html#c1...
  29. A

    Deriving Feynman rules from Lagrangian

    I've been given a small project to ease me into life as a PhD student and part of it involves working out Feynman rules for scalar bosons coupling to gauge bosons. I've been reading through Peskin and Schroder Chapter 9 and want to clarify if I've got my understanding right of how to do it...
  30. M

    Deriving Doppler Shift Using Spacetime Diagram

    Alright, I'm trying to derive the dopper shift using a spacetime diagram (see attached). If we model light pulses then we can derive the distance between the pulses in time, and hence the doppler shift... right? So, if we make some light pulses along some sort of time event in the x, cT frame...
  31. S

    Deriving the Spherical Unit Vectors

    Does anyone know how to derive the spherical unit vectors in the cartesian basis? Or a good link that might show how its done? I would also like to see it done for the cylindrical coordinates. I have tried to do it, especially for the spherical case, but i can only get r-hat. It would be...
  32. I

    Deriving the Statement on Strang's Linear Algebra Page 230

    I have a question from Strang's Linear Algebra on page 230. Does anyone know how to derive the attached statement?
  33. P

    Derive Sin(x+y) & Cos(x+y) Using Euler's Formula

    Can anyone tell me how to derive the sin(x+y) and cos(x+y) expansions? The ones that are like cos x sin y or sin y cos x + other stuff? Preferrably, could this be derived with Euler's formula alone? Or something not too geometric? (All those OAs and OBs and XBs and XYs on geometric diagrams...
  34. H

    Deriving Newton's Law of Gravitation: Understanding the Significance

    Newton's Law of Gravitation Derivative Hi, I was wondering if anyone could help me find the derivative of Newton's Law of gravitation [F=(GmM)/r^2] and what it means? What does the minus sign indicate? I'm kind of confused on the subject at hand and hopefully someone can help out. Thanks
  35. S

    Deriving the Derivative of ln(x^2+2)^(1/2)

    y = ln[\sqrt(x^2+2)] I changed it to y = ln[(x^2+2)^{1/2}] I know the derivative of ln = \frac {1}{x} I'm not sure how to proceed.
  36. C

    Deriving stiffness of a node in finite element theory

    I want to derive the theory of finite element using my own understanding. With this derivation i want to understand the fea theory of rod element I call the nodes as "points" in a structure. This scenario is for a simple one dimensional displacement of points(that is the single degree of...
  37. B

    Deriving the hydrostatic equilibrium equation.

    A question asks for me to show that the minimum pressure of a star is given by: P_{min}=\frac{GM^2}{8\pi R^4} where M and R are the mass and radius of the star. My answer goes like this: Gravitational force towards center = \frac{GM(r)\delta M(r)}{r^2} Pressure force outwards =...
  38. T

    Deriving the 4d continuity equation

    Well we start out with -\frac {d} {dt} \int_{V}^{} \sigma dV = \int_{\Pi}^{} \vec{J} \cdot d\vec{\Pi} Using the Gauss theorem \int_{V}^{} (\frac{ \partial {\sigma}}{ \partial {t}} + div \vec{J}) dV = 0 so \frac{ \partial {\sigma}}{ \partial {t}} + div \vec{J} = 0 and written in 4D...
  39. G

    What are the Dirac matrices used for in the Klein-Gordon equation?

    I'm trying to linearize Klein-Gordon equation, following Dirac's nobel lecture: (E^2 - (pc)^2 - (mc^2)^2) \psi = 0 (E + \alpha pc + \beta mc^2) (E + \alpha pc - \beta mc^2) \psi = 0 Expanding the equations yields: -\alpha and \beta commutes with E and p -\alpha^2 = \beta^2 = 1 -\alpha...
  40. L

    Maths problem: deriving expressions for the critical temperature/volume/pressure

    I have to show that for a van der Waals gas the critical temperature, volume and pressure are given by: T_c= \frac{8a}{27bR} V_c= 3nb p_c= \frac{a}{27b^2} I started off this way: Van der Waals states that for a non ideal gas the pressure is: P = \frac{nRT}{V-nb} - a...
  41. T

    Deriving the lorentz transforms

    It's a really easy question, I know, but I must be doing something stupid. Can someone please spell out how to get the right hand side matrix form out of the individual equations? http://img234.imageshack.us/img234/8497/lorentz25wv.jpg
  42. D

    Deriving Wien's Law from Planck's Formula

    As a refresher exercise in modern physics, I want to derive Wien's displacement law: \lambda_{max}T=2.898x10^{-3}mK from Planck's formula: R(\lambda)=(\frac{c}{4})(\frac{8\pi}{\lambda^4})(\frac{hc}{\lambda})(\frac{1}{\exp^(\frac{hc}{\lambda\kT})-1}) by differentiating R(\lambda) and...
  43. S

    Deriving the Coefficient of Rolling Friction for a Cart on an Incline

    Hello. I need some help with the following problem. There is a cart on an incline and a pulley with a suspended block. Assuming that (the force of friction)= (mu)(N) symbolically show that the coefficient of rolling friction for the car moving down the incline plane with a constant...
  44. O

    Geometric Series Derivation for Given Identities

    I am trying to derive the geometric series for the following given identities, \begin{array}{l} \frac{1}{{0.99}} = 1.0101010101... \; \; \; {\rm{ (1)}} \\ \frac{1}{{0.98}} = 1.0204081632... \; \; \; {\rm{ (2)}} \\ \end{array} Here is my answer for (1), \sum\limits_{n = 1}^\infty...
  45. N

    Deriving the Adiabatic Expression for a Van der Waals Gas

    For a van der Waals gas experiencing an adiabatic process derive the following expression: T(V-nb)^(R/Cv) = Constant I tried using PV^gamma = Constant with gamma = Cp/Cv and Cp - Cv = nR with PV = nRT but could not get it. Any hints? I would have to use Boyle's law to account for...
  46. W

    How Do You Solve the Damped Oscillator Equation Using Newton's Second Law?

    Using Newton's 2nd Law for a damped oscillator: ma = -kx - \alpha x which is a second order linear DE. To solve it we use the trial integrating factor e^{\lambda x} [/tex] to come to the root equation mx^2 + \alpha x + k = 0 where we can find our two solutions to be r_{1} \ and...
  47. D

    Can someone help me please?Help Needed: Deriving 4th Order PDE in One Variable

    For some reason i can't post in the calculus and beyond section but i was hoping someone could help me with this question eq.1 du/dt - fv = g*(dn/dx) eq.2 dv/dt + fu = g*(dn/dg) eq.3 du/dx+dv/dg=(1/(H)*(dn/dt) manipulate the equations to derivate a single PDE in one variable n which is...
  48. S

    Help Deriving the equation Ek=1/2mv^2

    Ok these are the equations I am allowed to use. Ep=mg(delta)h w=fd v_av=(delta)d/(delta)t (delta)d=v1(delta)t^2 + 1/2a(delta)t^2 V2=V1^2 + 2a(delta)d w=work done(j) f=force(Newtons) d=distance(m) v_av=average velocity t=time(secs) v2=final velocity v1=initial velocity a=acceleration...
  49. E

    Deriving the rate laws for first and second order reactions

    So, the average rate for a reaction of type A --> product is given by \text{rate} = -\frac{\Delta A}{\Delta t}. Also, \text{rate} = k \cdot \text{A}. The instantaneous rate for a reaction of that type is \lim_{\Delta t\rightarrow\0} -\frac{\Delta A}{\Delta t} = -\frac{dA}{dt}. Setting the...
  50. W

    Deriving the Value of the Sum in {_\lim {i} \rightarrow 0}

    Given the sum {_\lim {i} \rightarrow 0} \sum_{k=0}^{\frac{x}{i} - 1} i\sqrt{1 + i^{2n-2}((k+1)^{n} - k^{n})^{2}} I want to know how to derive to the value of this sum exactly. This is actually the value of the lenghts of a curve from a point to the origin of the form f(x) = x^n... I thought...
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