Spring Constant
Definition
A number that measures a spring's stiffness — how much force is needed to stretch or compress it by a given distance.
Symbol: · Unit: N/m
Technical definition
The proportionality constant k in Hooke's law, F = −kx. Units of N/m. A larger k means a stiffer spring: more force per unit of extension. It depends on the spring's material, wire thickness, and coil geometry.
Example
A spring with k = 200 N/m needs 20 N to stretch 10 cm. A car's suspension springs have k values in the tens of thousands of N/m.
Common confusion
The spring constant is not universal — every spring has its own k. And Hooke's law only holds within the elastic limit; stretch too far and the spring permanently deforms, and F = −kx no longer applies.