Variable Definition and 1000 Threads

A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates.
This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either:

Intrinsic variables, whose luminosity actually changes; for example, because the star periodically swells and shrinks.
Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes eclipses it.Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle.

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  1. E

    Can anyone explain this derivation of the variable mass equation?

    This question stems from one of the recent homework threads. I'm familiar with the derivation given here regarding mass accretion and ejection, where the general idea is to define a system around body and all of the incoming/leaving mass so that we can once again apply NII to the whole thing. I...
  2. D

    How Does a Variable Mass Affect a Simple Pendulum?

    Hello, I've got to rationally analice the form of the solutions for the equations of motion of a simple pendulum with a varying mass hanging from its thread of length ##l## (being this length constant). I approached this with lagrangian mechanics, asumming the positive ##y## direction is...
  3. B

    How do I know when to factor out a variable?

    Take the equation for gamma. I know how to get from step 1 to gamma. How would I do that if I have not have seen the instructions? There are many ways to factor step 1 without getting the same values of ## gamma = \frac 1 {\sqrt {1 - \frac {v^2} {c^2}}} ## step 1 = Speaking of factoring and...
  4. M

    Adding a variable to a Lagrangian

    Would the following: $$ L = m(\vec{\dot r + \vec v})$$ (constant velocity added to above eq.) lead to equivalent euler-lagrange equations due to the fact that the ratio of T and V is unaffected by an increase in constant velocity? And would this be an example of energy conservation?
  5. Jonathanos

    Courses Complex Analysis Courses or Complex Variable Courses?

    Hello, My university offers a couple Complex Analysis courses, among them there is one with the following description: Introduction to complex variables: "substantial attention to applications in science and engineering. Concepts, calculations, and the ability to apply principles to physical...
  6. W

    I Taylor series and variable substitutions

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  7. F

    Understanding the PMF of a Random Variable: A Brief Overview

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  8. F

    How to operate a Variable DC source

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  9. E

    B How do we interpret a random variable?

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  10. Adesh

    Confusion about the independent variable of function in magnetostaics.

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  11. A

    Motor / transformer variable frequency control

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  12. nima_kheradhoosh

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  13. A

    A Third and fourth central moment of a random variable

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  14. karush

    MHB 004- USMA(WP) entrance exam question independent variable

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  15. R

    Change of variable in a double integral

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  16. G

    MHB Calculating Total Cost with Variable n: C = 7500 + 8n

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  17. R

    Engineering Find the Minimal SOP Using a 5 Variable K-Map

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  18. SoulOfSword_

    How Do You Find Extragalactic Cepheid Variable Databases?

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  19. E

    Rocket moving through a cloud of dust, variable mass problem

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  20. F

    I Distribution of a sample random variable

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  21. nomadreid

    I Quantum state variable for entangled system

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  22. CheesyPeeps

    Force on side of tank filled with liquid of variable specific weight

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  23. Math Amateur

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  24. S

    Finding truth value of each propositional variable.

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  25. Math Amateur

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  26. M

    MHB Cdf, expectation, and variance of a random continuous variable

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  27. WMDhamnekar

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  28. BiGyElLoWhAt

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  29. X

    Determining the optimal resistance of a variable resistor

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  30. W

    I Variable mass F=ma versus Rocket F=ma

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  31. J

    A Which is the quantized variable in quantum gravity?

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  32. N

    I Variable transformation for a multivariate normal distribution

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  33. Protea Grandiceps

    I X variable in damping force equation for damped oscillation?

    Hi, for ease of reference this posting is segmented into : 1. Background 2. Focus 3. Question 1. Background: Regarding (one, linear, second-order, homogeneous, ordinary, differential) equation describing the force in a non-driven, damped oscillation: F = m.a = -k.x - b.v F =...
  34. uzi kiko

    A Estimate the source of a variable when there are several distributions

    Hello everyone In my study, I inject a different amount of fluid in each experiment, such as 1 ml, 2 ml..., and test the change in the general dielectric properties of the solution. Now that I have done much (over 100) measurements for each injection in a specific volume, one can see that for...
  35. I

    Use a variable substitution to get into a Bessel equation form?

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  36. Suppaman

    B Is time a true variable in the scheme of things?

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  37. A

    A Can we create a random variable using QED effects?

    Quantum Electrodynamics (QED) has some observable effects such as the lamb shift, which is mainly caused by the vacuum polarization and the electron self-energy. These effects contribute to the "smearing" of the electron in an unpredictable manner, other than the uncertainty we already have...
  38. Eucliwood

    Work done on an object given a variable mass

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  39. R

    Choosing Free Variable for Generalized Eigenvector

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  40. user366312

    A Question about the Poisson distributed of random variable

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  41. W

    I Continuous variable entanglement

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  42. E

    A variable mass problem with friction

    Homework Statement A water tank with a total mass of m0 is moving on a horizontal road with a coefficient of friction equals to μ. At t=0 water starts to come out of the tank with a velocity equal to u0 in relation to the tank. Each second the mass of water that comes out is λ. Find the...
  43. E

    Why Is Momentum Conserved in a Variable Mass System Like a Sand-Laden Cart?

    Homework Statement A cart with no motor moves on a plane. At t=0 it has a mass equal to m0 and some velocity. Each second sand with a mass of α comes out of the cart with a velocity of 0 in relation to the plane. What is the equation of motion of the cart? Answer: dV/dt=αv(t)/(m0-αt) Homework...
  44. Ranku

    I Variable Dark Energy: Would P Remain Constant?

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  45. DrClaude

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  46. CivilSigma

    Find the PDF in terms of another variable

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  47. R

    Finding formulas for the variable "a" and summations

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  48. Ottodomus

    Fortran Help with a warning: Uninitialized Variable

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  49. jk22

    B Usage of variable in integration

    When solving differential equations the following scripture can arise, for example: $$\int \frac{df}{\sqrt{\sin(\theta)^2-f^2}}$$ If the change of variable ##f=\sin(\theta)\sin(u)## Is performed, do the letters ##f,\theta## shall be considered independent or is...
  50. N

    Partial Differential Equation with variable coefficients

    Homework Statement This question relates to a very large project I have been assigned in a course on mathematical methods in structural engineering. I have to solve the following equation, in a specific way: (17) Now we have to assume the following solution: (18) It wants me insert...
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