Physic Labs

Oscillations and waves

Energy in simple harmonic motion

Track kinetic energy K=12mv2K=\tfrac12mv^2 and elastic potential energy U=12kx2U=\tfrac12kx^2 of a frictionless oscillator and verify that the mechanical energy E=12kA2E=\tfrac12kA^2 stays constant while the two forms exchange.

High school

Equipment

  • Virtual mass–spring oscillator without friction
  • Sliders “Biên độ A” (amplitude), “Khối lượng m” (mass), “Độ cứng k” (stiffness)
  • Instantaneous energy bars: red for potential, blue for kinetic
  • “Tạm dừng” (pause) button to freeze and read a state

Procedure

  1. Watch the energy exchange

    Let the oscillator run and watch the red potential bar and the blue kinetic bar rise and fall out of phase. The vertical marker tracks the instantaneous state; notice that the total height of the bars stays constant, illustrating E=K+U=12kA2E=K+U=\tfrac12kA^2.

  2. Check the energy at special points

    Press “Tạm dừng” when the mass passes equilibrium and again at maximum displacement. At x=0x=0 all energy is kinetic, Kmax⁡=12kA2K_{\max}=\tfrac12kA^2; at x=±Ax=\pm A it is all potential. Read the bars and confirm K=12k(A2−x2)K=\tfrac12k(A^2-x^2) at an intermediate point.

  3. Vary A, m and k

    Double the amplitude A and observe the total energy quadruple, since E∝A2E\propto A^2. Then increase k at fixed A to raise E, and increase m: the total energy is unchanged, but the motion slows because the period T=2πm/kT=2\pi\sqrt{m/k} grows.

Simulation

Experiment history

Galileo Galilei studied pendulum motion around 1600 and reported that a pendulum bob returns nearly to its release height — an early observation of mechanical-energy conservation before the concept had a name. Christiaan Huygens put these ideas on a quantitative footing in Horologium Oscillatorium (1673), analyzing pendulum oscillations for clock design. The spring oscillator entered theory through Robert Hooke's law of elasticity, announced in 1676 and published in 1678. Treating energy explicitly came later: the term “kinetic energy” and systematic use of 12mv2\tfrac12mv^2 belong to the 19th century, when conservation of energy became a unifying principle of physics.

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