A stretched or compressed spring pulls or pushes an attached cart toward the middle. It does not always pull left or always pull right. The force changes direction across the middle. A moving cart can pass the middle even when the spring force is zero. Multiply spring stiffness by displacement to find the force size. Its direction is back toward the middle. Hooke’s law applies only over a suitable elastic range. Real springs can damp, change stiffness or deform permanently. The model keeps total mechanical energy constant and reports the exchange between elastic and kinetic forms. Its force direction and timing follow the equations, while the screen drawing has an explicitly illustrative length scale.
Forces, motion and energy · Discover & try
Why does a stretched spring pull back?
Reading level 5 of 5 · AdvancedChange
Word help
Equilibrium
The position where the ideal spring exerts zero restoring force.
Stiffness
The spring factor k, measured in newtons per metre.
Elastic energy
Energy stored when the spring is displaced.
Watch · Try · Explain
See how it works
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Ideal linear, massless spring and frictionless horizontal cart, within the elastic range.
What to look for
- The force points toward the middle on both sides.
- The same cart completes its back-and-forth motion sooner.
- The same spring now takes longer for a complete cycle.
Explain what you noticed
A separate ideal spring has stiffness 30 N/m and is displaced 0.2 m to the right. What spring force acts on its cart?
Keep this idea: Within its elastic range, an ideal spring’s restoring force points toward equilibrium and grows with displacement.
Follow the sources
- OpenStax, Rice University — Hooke’s Law: Stress and Strain Revisited
- OpenStax, Rice University — Common Forces
Source material checked 2026-10-29. Explanations and activities by Nepedia. Source links do not imply endorsement.
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