Is a simple pendulum simple harmonic motion?

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SUMMARY

A simple pendulum exhibits simple harmonic motion (SHM) when the angle of displacement is small. The restoring force for a simple pendulum is given by F = -mg sin(θ), which is non-linear. However, for small angles, sin(θ) approximates to θ, allowing the restoring force to be expressed as F = -mgx/l, where x is the arc length and l is the length of the pendulum. This linear approximation confirms that the simple pendulum behaves as a simple harmonic oscillator under these conditions.

PREREQUISITES
  • Understanding of simple harmonic motion (SHM)
  • Knowledge of restoring forces in physics
  • Familiarity with trigonometric approximations
  • Basic concepts of pendulum mechanics
NEXT STEPS
  • Study the derivation of the restoring force for a simple pendulum
  • Explore the conditions under which SHM occurs in various systems
  • Learn about the limitations of the small angle approximation
  • Investigate the differences between linear and non-linear restoring forces
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Students of physics, educators teaching mechanics, and anyone interested in the principles of oscillatory motion and pendulum behavior.

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I'm wondering this because my textbook says that for small angles it is, but we learned that for simple harmonic motion to occur there must be a linear restoring force.. eg F= -kx.. but for the simple pendulum the restoring force is F= -mgsin(theta).. wouldn't this not be linear?
 
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Well you see for small angles θ, sinθ≈θ so that the restoring force is F=-mgθ.

And now you know θ=x/l (x=arc length and l=length of pendulum)

so F=-mgx/l
 
Ohh okay, makes sense. Thank you!
 

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