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In Hooke's law, F = -kx, what are the SI units of the spring constant k?

Newtons per meter (N/m): force per unit of stretch.

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  1. Newtons per meter ✔
  2. Newton meters
  3. Newtons per square meter

Why: k tells you how many newtons it takes to stretch or squeeze the spring by one meter. A bigger k means a stiffer spring. The minus sign means the spring pushes back toward its rest length.

Huh, didn't know that: Hooke's law only holds up to the proportionality limit; stretch too far and force is no longer proportional.

The dad joke
Why was the spring so good at relationships? It always bounced back.
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References

Answer: Newtons per meter. k tells you how many newtons it takes to stretch or squeeze the spring by one meter. A bigger k means a stiffer spring. The minus sign means the spring pushes back toward its rest length.

  1. OpenStax College Physics 2e: 16.1 Hooke's Law, Stress and Strain Revisited openstax.org/books/college-physics-2e/pages/16-1-hookes-law-stress-and-strain-revisited
    the larger the force constant, the greater the restoring force, and the stiffer the system
    Checked 2026-10-10.
  2. OpenStax University Physics Volume 1: 12.4 Elasticity and Plasticity openstax.org/books/university-physics-volume-1/pages/12-4-elasticity-and-plasticity
    the largest stress value beyond which stress is no longer proportional to strain
    Checked 2026-10-10.

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