Choose the arrangement (A alone, series or parallel) and the two springs.
Add a load with +. Read the total extension x and press ● Record.
Repeat for several loads and arrangements. The Data & analysis tab fits a line for each arrangement:
its gradient is the effective spring constantkeff.
Load & unload (checkpoint): one spring or the rubber band. Add masses, then take them off again. The Graph
tab draws the loading curve (orange) and the unloading curve (blue), the elastic limit E of a steel spring and
the hysteresis loop of the rubber band.
The physics
Series (one below the other): each spring carries the whole load, so the extensions add:
x = F/kA + F/kB ⇒ 1/keff = 1/kA + 1/kB.
Parallel (side by side, bar kept level): both springs have the same extension and share the load:
F = kAx + kBx ⇒ keff = kA + kB.
A rubber band does not obey Hooke's law: its F–x graph curves, so it has no single k.
Hysteresis: the band's unloading curve lies below its loading curve. Area under the loading curve = energy stored;
area under the unloading curve = energy given back; the loop area = energy turned into heat in the band.
Past the elastic limit E a steel spring is permanently stretched: it does not return to its original length.
Series and parallel springs are not in the IB SL guide; they extend Hooke's law and match the "car suspension"
problem (four springs share the car's weight). Model: light springs and bar, below the elastic limit (except in
Load & unload, where steel springs soften past E and keep 30 % of the extra stretch).