Hang masses: add 50 g slotted masses with ▲ and ▼ (or type any load, up to 100 kg). Read the pointer on the ruler; the
extension x is the pointer reading minus the unloaded reading. Press ● Record for each load.
Set each value with ▼ and ▲ (hold to go faster; the ↑ ↓ keys or the mouse wheel in the box also work, Shift = ×10), or type a value in the box. ↺ puts it back to its start value. Outside the classroom range the box turns amber ⚠: fine to explore, but the lab can't do this.
Move the pointer over any graph (or tap it): a dashed line shows the values where it cuts each curve, or the values of the nearest data point.
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.
Newton's laws
The badge above the scene says which law applies at this moment: 1st law — at rest or moving at a constant velocity, the resultant force is zero (ΣF = 0); 2nd law — accelerating, ΣF = ma. The table under the free-body diagram adds up the forces (ΣF) and compares them with m a (▾ folds it). Tick 3rd-law pairs to see every force with its partner: the same size and type, in the opposite direction, acting on the other body (the Earth, the floor, the string, the fluid…).