Measure extension in a supervised spring experiment
Measure an unloaded reference length and collect matched load and extension readings.
Section P1.5.1 · Effects of forces
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Use a ruler and a zeroed reference.
- Convert mass to gravitational load using the supplied field strength.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which readings determine extension?
What you will learn
- Describe a load–extension procedure.
- Control reading errors and distinguish measured length from extension.
Pair each load with its extension
In a supervised setup, secure a spring to a stable clamp, place a ruler beside it and use a pointer on the lower end. Record the unloaded reference length or position. Add modest known loads in steps, wait for oscillations to settle and record the new position at eye level. Extension is each loaded reading minus the unloaded reading.
Define the reference consistently. If a load hanger is part of the unloaded setup, subsequent loads are the added forces above that baseline; otherwise include the hanger in the total load and measure a true no-load reference. Do not alternate conventions halfway through the table. When loads are given as masses, use W = mg to record force in N.
Make the procedure reliable and supervised
Keep the ruler fixed, place the pointer close to it to reduce parallax, repeat careful readings and choose loads within the teacher's approved range. A stable support and protection from a falling load are part of the real setup. Written planning does not replace supervision or demonstrate practical competence.
Original example readings use unloaded length 12.0 cm and loaded lengths 12.5,13.0,13.5,14.0 cm under loads 1,2,3,4 N. Their extensions are 0.5,1.0,1.5,2.0 cm. Repeat or unload cautiously to investigate behaviour; do not assume a material is permanently undamaged merely because the table looks regular.
Sources for this lesson
Pause and explain
The lower pointer is still oscillating. What should you do before recording a static extension?
Worked example
Unloaded length is 12.0 cm; lengths at 1,2,3,4 N are 12.5,13.0,13.5,14.0 cm. Find extensions.
Show the worked solution
- Use the same unloaded reference for each reading.
- Subtract 12.0 cm from each loaded length.
- Extensions are 0.5,1.0,1.5,2.0 cm.
Answer 0.5, 1.0, 1.5 and 2.0 cm.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
For reference length 12.0 cm and loaded length 14.0 cm at 4 N, find extension.
Give me a hint
Subtract the unloaded reference before entering the table.
Compare my reasoning
- Reference is 12.0 cm.
- Extension = 14.0 − 12.0.
- Pair 2.0 cm with load 4 N.
2.0 cm at 4 N.
Look for these in your work
- Use the reference subtraction.
- Pair the correct load and extension.
Reference position is 10.2 cm and loaded positions are 10.8,11.4,12.0 cm at 1,2,3 N. Complete the extension column.
Give me a hint
Use the same baseline for all three observations.
Compare my reasoning
- 10.8 − 10.2 = 0.6 cm.
- 11.4 − 10.2 = 1.2 cm.
- 12.0 − 10.2 = 1.8 cm.
0.6, 1.2 and 1.8 cm.
Look for these in your work
- Retain matched rows.
- Keep the baseline fixed.
A student resets the ruler's zero at each loaded position and records zero extension every time. Explain the error and repair the procedure.
Give me a hint
A changing zero cannot preserve comparison with the unloaded state.
Compare my reasoning
- Each reset removes the previous displacement from the reading.
- Fix the ruler and record one unloaded reference.
- Subtract that same reference from every settled loaded reading.
Keep a fixed ruler and common unloaded reference; subtract it from each loaded reading.
Look for these in your work
- Identify the changing-reference error.
- Describe a consistent correction.
Common mistakes
- Do not plot total length as extension.
- Keep the hanger and reference convention consistent.
- Read after oscillation settles and at eye level.
What can you explain now?
A spring has reference length 10.2 cm and loaded length 11.7 cm. What is extension?
Compare with the explanation
1.5 cm.
Subtract the reference from the loaded reading.
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Make it stick
Sketch a labelled setup and explain how its pointer, reference and load table work together.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.