Mar 16
A Triple Spring-Mass Pendulum Just for The Fun of Physics
We model the mass positions as
r₁ = (x₁, y₁), r₂ = (x₂, y₂), r₃ = (x₃, y₃)
with y positive downward in the simulation. The three spring segments are
r₁ = r₁ − (0,0)
r₁₂ = r₂ − r₁
r₂₃ = r₃ − r₂
Each spring applies a Hooke force along its own direction,
F(r; k, L) = −k (|r| − L) (r / |r|)
and each mass also feels gravity,
Fgᵢ = (0, mᵢ g)
So the equations of motion are
m₁ r̈₁ = Fg₁ F(r₁; k₁, L₁) − F(r₁₂; k₂, L₂)
m₂ r̈₂ = Fg₂ F(r₁₂; k₂, L₂) − F(r₂₃; k₃, L₃)
m₃ r̈₃ = Fg₃ F(r₂₃; k₃, L₃)
We integrate these ODEs forward with RK4 using a small dt. Different scenes come from changing the mass ratios and from giving the third mass a small initial kick.
The yellow trail is the path of the third mass.
The inset phase portraits show the same motion in state space:
(x₃, vₓ₃) and (−y₃, vᵧ₃)
When those curves stay tight and loop cleanly, the motion is more regular. When they spread, fold, and smear, energy is being redistributed across the whole chain between gravity, spring stretch, and kinetic motion.
#NonlinearDynamics #CoupledOscillators #SpringPendulum #ChaosInMotion #ComputationalPhysics #MathematicalVisualization
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Jan 16
A Triple Spring-Mass Pendulum System.
Three point masses hanging in a chain, connected by springs, moving in a vertical plane. Gravity keeps trying to pull everything straight down, while the springs keep trying to pull each pair back toward its rest length. Because the links are springs and not rigid rods, the motion isn’t locked to circular arcs. The chain can stretch and compress, so energy can slosh between swinging and breathing.
The model is straight Newtonian mechanics. Write the mass positions as
r₁ = (x₁, y₁), r₂ = (x₂, y₂), r₃ = (x₃, y₃)
with y positive downward in the simulation. The three spring segments are
r₁ = r₁ − (0,0)
r₁₂ = r₂ − r₁
r₂₃ = r₃ − r₂
Each spring contributes a Hooke force along its own direction,
F(r; k, L) = −k (|r| − L) (r / |r|)
and each mass gets gravity
Fgᵢ = (0, mᵢ g)
So the net force balance is
m₁ r¨₁ = Fg₁ F(r₁; k₁, L₁) − F(r₁₂; k₂, L₂)
m₂ r¨₂ = Fg₂ F(r₁₂; k₂, L₂) − F(r₂₃; k₃, L₃)
m₃ r¨₃ = Fg₃ F(r₂₃; k₃, L₃)
We integrate these ODEs forward with RK4 using a small dt, then stitch multiple scenarios back-to-back by changing mass ratios and/or giving the third mass a small initial kick.
The yellow trail is the path of the third mass. The inset phase portraits are the same idea but in state-space:
(x₃, vₓ₃) and (−y₃, vᵧ₃)
When those curves tighten into neat loops, the motion is more regular. When they swell, fold, and smear, you’re watching energy shuffle between gravity, spring stretch, and kinetic motion across the whole chain.
#NonlinearDynamics #CoupledOscillators #SpringPendulum #ChaosInMotion #ComputationalPhysics #MathematicalVisualization
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