The spring constant k measures how stiff a spring is — the force needed per metre of stretch, k = F/x in newtons per metre. Hang masses on the virtual spring below, pin each reading to the graph, and read k straight off the slope, exactly as the classroom experiment does.
Start with the mass slider. Every notch loads more weight onto the virtual spring, and the readouts update instantly: the stretching force F in newtons, the extension x in centimetres, and the value of k = F/x for that single reading. Keep your eye on the dashed level lines — the gap between the unloaded and loaded positions is the extension, never the spring's full length, and that distinction alone prevents the most common calculation error.
Press Plot point after each load to pin the reading onto the force–extension chart, then change the mass and pin again. Five or six pins trace a straight line through the origin, and the slope readout reports its gradient — that gradient is the spring constant, exactly as measured in the classroom experiment. You can double-check any pinned reading by hand, or drop the same numbers into our Spring Constant Calculator to solve for force or extension as well.
The stiffness slider swaps the spring under test. Load identical masses onto a stiffer spring and every extension shrinks, so the plotted line stands steeper — steeper always means stiffer. The linear pattern the simulator draws is the proportionality described by Hooke's law, and it holds only while a real spring still returns cleanly to its starting length.
One experiment worth running deliberately: double the extension and compare the stored energy, which grows with the area under the plotted line. It quadruples rather than doubles — the squared relationship our guide to elastic potential energy unpacks in full. Seeing that area grow on the chart makes the algebra feel obvious.
It calculates the spring constant k = F/x from the hanging mass and the extension it produces, in newtons per metre. Each reading shows the weight F = mg, the extension x, and the resulting k, while the chart's best-fit slope gives k the graphical way. Both routes should agree, which is the whole point of the exercise.
Because the same force is being applied to a stiffer spring. Extension follows x = F/k, so doubling k halves the stretch for any given load. The chart shows the same fact as geometry: a stiffer spring plots as a steeper line, meaning less horizontal extension for the same vertical force.
Use it as a rehearsal and a checking tool rather than a replacement. It teaches the method — load, read, plot, take the slope — and predicts what good data should look like, but coursework and exams expect measurements from real apparatus. Run it before the practical, then again afterwards to sanity-check your measured k.
Mass is entered in grams and converted internally, force is shown in newtons using F = mg with g = 9.81 m/s2, extension is displayed in centimetres but computed in metres, and the spring constant is reported in newtons per metre (N/m). Divide any k by 100 to read it as newtons per centimetre.