Hang masses: add 50 g slotted masses with + and −. Read the pointer on the ruler; the
extension x is the pointer reading minus the unloaded reading. Press ● Record for each load.
Set the values with the sliders, or type a value in the box next to a slider and press Enter. A value outside the allowed range is set to the nearest allowed value.
Tick Mystery bag to hang an object of unknown mass, and ±0.1 cm to read the ruler like in the lab.
Load a spring beyond its elastic limit and then unload it: it no longer returns to its original length.
↺ New spring replaces it.
Push / pull: hold the block on a frictionless table and stretch or squash the spring.
Load & unload (checkpoint): add masses one by one, then take them off again. The Graph tab draws the
loading curve (orange) and the unloading curve (blue). Try a steel spring below and beyond its elastic limit
E, and the rubber band.
The Data & analysis tab plots load F against extension x with error bars.
The physics
Hooke's law: FH = −kx. The spring force is proportional to the extension and points back towards the natural length.
Hanging at rest: FH = W = mg, so k = mg / x = gradient of the F–x graph.
Beyond the limit of proportionality the graph curves; beyond the elastic limit the spring is permanently stretched.
Hysteresis: a rubber band's unloading curve lies below its loading curve. The area under the loading curve is the
energy stored; the area under the unloading curve is the energy given back. The area of the loop is the energy
turned into heat (internal energy) in the band.
Model: the investigation spring has k = 25.0 N m⁻¹ (like the Forces investigation); the Station 3 spring
29.4 N m⁻¹. Past the limit the spring is modelled as softer and keeps 30 % of the extra stretch; here the limit of
proportionality and the elastic limit are taken as the same point E. Rubber band: F = 8x + 250x² (x in m) on loading.