Physic Labs

Oscillations and waves

The spring–mass oscillator

Study a mass on an ideal spring obeying Hooke's law F=−kxF = -kx. Verify the period T=2πm/kT = 2\pi\sqrt{m/k} and angular frequency ω=k/m\omega = \sqrt{k/m} as mass, stiffness, and amplitude vary.

High school

Equipment

  • Ideal spring with a hanging mass on a vertical plane
  • Sliders for mass m and stiffness k
  • Amplitude slider A and a Pause button
  • Displacement/force plots and a quantity readout

Procedure

  1. Check the linear restoring force

    Run the simulation and Pause at several displacements: the spring force always points toward equilibrium and grows with ∣x∣|x|, as F=−kxF = -kx. Change stiffness k and observe that the same displacement yields a different force.

  2. Measure the period versus m and k

    At fixed k, raise m through several values and time one full oscillation: the period grows as m\sqrt{m}. Then raise k at fixed m: the period falls as 1/k1/\sqrt{k}. Compare each point with T=2πm/kT = 2\pi\sqrt{m/k}.

  3. Verify independence from amplitude

    Hold m, k fixed and change amplitude A: the period must stay the same — the signature of harmonic motion from a linear force. Also watch energy: mechanical energy E=12kA2E = \frac{1}{2}kA^2 grows quadratically even though T is constant; predict E before moving A.

Simulation

Experiment history

In 1660 Robert Hooke found a spring's extension proportional to the applied force and published it in 1676 as the anagram "ut tensio, sic vis" — as the extension, so the force. He used springs as balance regulators in watches around 1675, contesting priority with Huygens. Harmonic motion took form once Newton placed displacement-proportional force into differential equations (1687). In 1878 Lord Rayleigh's Theory of Sound systematized the spring–mass oscillator as the standard model for every small oscillation about equilibrium — a principle running through mechanics, electronics, and solid-state physics.

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