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4.2.3Unit 4: Energy, Environment, Microbiology and Immunity

Core Practical 8: Determining the Tensile Strength of Plant Fibres — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 16 of 28 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5Principle

The tensile strength of a fibre is the maximum load it can carry before it breaks.

Principle
Why it matters
  • Why it matters Knowing the breaking load tells you how strong a rope or cloth made from the fibre would be.
Measurement
  • Measurement The mass that is on the fibre at the moment it snaps represents its breaking load.
Comparison
  • Comparison Fibres from different plants or treatments can be compared fairly if tested in the same way.
Link to structure
  • Link to structure Differences in strength reflect cell wall features such as microfibril arrangement, thickening and lignin.

Part 2 of 5Method

The apparatus is a retort stand with a clamp, a set of masses and the fibre samples.

1
Attach one end of the fibre firmly to the clamp on a retort stand and hang a mass holder from the other end.
2
Add masses one at a time, gently, until the fibre breaks, and place a cushion on the floor to protect the masses.
3
Record the total mass that was on the fibre when it broke.
4
Repeat with several samples of the same fibre to improve accuracy and to identify anomalous results.
5
Calculate the mean breaking mass for each type of fibre and compare them.

Part 3 of 5Controls and Evaluation

Same length
  • Same length All fibres should be of the same length and width, because a longer or thicker fibre would change the result.
Same conditions
  • Same conditions Keep temperature, humidity and the way the fibre is attached the same throughout the investigation.
Small steps
  • Small steps Adding smaller masses near the breaking point increases the precision of the reading.
Repeats
  • Repeats Several repeats allow a mean to be found and reduce the effect of random variation between fibres.

Part 4 of 5Worked Example

Question

  • Five fibres of the same length from one plant broke under masses of 2.1, 1.9, 2.3, 2.0 and 2.2 kg.
  • Calculate the mean breaking mass and the mean breaking force (g = 9.81 N/kg).

  1. Sum of masses = 2.1 + 1.9 + 2.3 + 2.0 + 2.2 = 10.5 kg.
  2. Mean mass = 10.5 ÷ 5 = 2.1 kg.
  3. Force = mass × g = 2.1 × 9.81 = 20.6 N (to 3 significant figures).

Answer Mean breaking mass = 2.1 kg, so the mean breaking force is about 20.6 N.

Part 5 of 5Exam Checklist & Tips

4.2.3 – Key Points for the Exam

  • Tensile strength The maximum load a fibre can bear when pulled before it breaks.
  • Breaking load The mass or force at which the fibre snaps.
  • Control variable A factor kept constant so that it does not affect the results.
  • Anomalous result A result that does not fit the pattern of the other repeats.

Common Mistakes

  • Using fibres of different lengths or thicknesses, which makes the comparison unfair.
  • Recording the last mass added before the break rather than the total mass on the fibre when it broke.
  • Relying on a single test instead of repeating and calculating a mean.
  • Dropping masses suddenly instead of adding them gently, which can break the fibre early.

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