Hooke's Law. Stretch it.

1. Suspend the spring vertically alongside a fixed metre rule. Attach a horizontal pointer at the bottom loop to eliminate parallax.
2. Record the initial pointer reading L₀ (the unstretched spring length).
3. Hang a 100 g mass (weight = 1.0 N if g = 10 N/kg) and record the new pointer reading L.
4. Calculate extension x = L − L₀.
5. Add successive 100 g masses up to ~500 g and record at each step.
6. Remove the masses in reverse order to confirm the pointer returns to L₀ (the spring has not exceeded its limit of proportionality).

Analytical control: plot Load F / N (y-axis) against Extension x / mm (x-axis). The linear region passes through the origin with gradient = k. The point where the line begins to curve is the limit of proportionality.

• Parallax when reading the rule — fit a horizontal pointer to the bottom of the spring and view perpendicular to the scale.
• Oscillation after loading — wait for the spring to come to rest before reading.
• Limit of proportionality exceeded — verify reversibility by unloading and rechecking L₀.
• Spring not vertical — clamp the support firmly and check with a plumb line.
• Mass uncertainty — manufacturer slot masses are ± 1 %. For higher accuracy, weigh each on a balance.

• Steel helical spring
• Mass hanger with 100 g slotted masses (×5)
• Retort stand with clamp and boss
• Metre rule (resolution ± 1 mm)
• Horizontal pointer attached to the bottom spring loop
• Plumb line (to verify vertical alignment)

• 1.5.1 Effects of forces — state Hooke's law: the extension of a spring is proportional to the load applied to it, up to the limit of proportionality. Recall and use F = k · x.
• 1.5.1 — define the spring constant k = F / x; define the limit of proportionality.
• 1.1 Measurement techniques — use a metre rule to measure length; eliminate parallax with a pointer.
• Paper 6 — record results in a table with headers showing quantity / unit; plot a graph with sensible scales and a line of best fit; calculate a gradient using a large triangle on the line; describe one source of error and one precaution.