6.1.2—The terms load, extension, compression and limit of proportionality

Load is the applied force; extension is the increase in length and compression the decrease. The limit of proportionality is where extension ceases to be directly proportional to load.

Read these terms from a force–extension graph and distinguish proportional behaviour from later elastic or plastic behaviour.

If a spring extends 2 mm under 4 N and remains proportional, 8 N predicts 4 mm; beyond the limit that scaling may fail.

The limit of proportionality is not automatically the breaking point or the elastic limit; those are separate boundaries.