Hooke's Law

Hooke’s law is expressed as:

$F = kx$

where $F$ is the applied force (N), $k$ is the spring constant (N/m), and $x$ is the extension (m).

The law applies only within the limit of proportionality. Beyond this point, the force-extension graph curves and the spring may be permanently deformed.

The spring constant $k$ is the gradient of the straight section of a force-extension graph. A larger $k$ means a stiffer spring.