Approximations for small oscillations

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SUMMARY

The discussion focuses on approximating small oscillations using the formula from Landau & Lifgarbagez mechanics. The key equation presented is δl = [r² + (l + r)² - 2r(l + r)cosθ]¹/² - l, which simplifies to δl ≈ r(l + r)θ²/2l for small angles. The participants emphasize the use of Taylor expansion techniques to derive the approximation, specifically applying the small angle approximation cos(θ) ≈ 1 - θ²/2 and expanding √(1+x) for simplification.

PREREQUISITES
  • Understanding of Taylor series expansion
  • Familiarity with small angle approximations in trigonometry
  • Basic knowledge of mechanics as outlined in Landau & Lifgarbagez
  • Ability to manipulate algebraic expressions involving square roots and trigonometric functions
NEXT STEPS
  • Study Taylor series and their applications in physics
  • Learn about small angle approximations and their significance in mechanics
  • Explore the derivation of the cosine function's Taylor series
  • Investigate the mathematical manipulation of square roots in physics equations
USEFUL FOR

Students of physics, particularly those studying mechanics, as well as educators looking to explain the concept of small oscillations and approximations in mathematical terms.

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Homework Statement



Basically the issue is Landau & Lifgarbagez mechanics says

δl = [r2 + (l + r)2 - 2r(l + r)cosθ]1/2 - l ≈ r(l + r)θ2/2l


Homework Equations



θ much less than 1

The Attempt at a Solution



I've no idea how to get the thing on the far right. I'm assuming it's Taylor expansion or something like that but that's not something any of my classes have really explained. Also this isn't homework, I'm on summer holidays.
 
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Can you massage the formula into
\delta l = l \sqrt{1 + \frac{2r(l+r)}{l^2}(1-\cos \theta)} - l? Then all you need to do is to do Taylor expansions for 1-cos θ and √(1+x).
 
try using the cos(theta)= 1 - (theta^2)/2 approx for small angles in radians
 

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