Concept preview

What you will be able to do

1. 01State Hooke's law and define the spring constant
2. 02Calculate spring force from extension (F = kΔx)
3. 03Interpret a force–extension graph

Grab a spring and stretch it. Stretch it twice as far and it fights back twice as hard — that simple, reliable rule is Hooke's law, and it runs everything from kitchen scales to car suspensions. In symbols: $F = k\Delta x$. Here $\Delta x$ is how far you've stretched (or squashed) the spring from its natural length, and $k$ is the spring constant in newtons per metre (N/m). A big $k$ means a stiff spring — it takes a lot of force per metre of stretch.