Practical: Determining the Tensile Strength of Plant Fibres (Edexcel A Level Biology (A) SNAB): Revision Note

Practical: Determining the Tensile Strength of Plant Fibres

• The tensile strength of a fibre is the maximum force it can withstand before breaking, per unit cross-sectional area (force ÷ cross-sectional area)

  • For example, this information would be important when determining the strength of a rope made of plant fibres

Apparatus

• Plant fibres

• Retort stand (clamp stand)

• Clamp

• Weights

Method

• The fibre should be attached to a clamp stand

• Attach a weight on the other end of the plant fibre

• Carefully continue to add one weight at a time until the fibre breaks

• Record the mass at which the fibre broke

• To calculate tensile strength

  • convert this mass to a force (N = mass in kg x 9.81)

  • measure the diameter of the fibre to work out its cross-sectional area

tensile strength = force ÷ cross-sectional area

• To increase the accuracy of your results, this process should be repeated with more samples of the same plant fibre

  • These values can be used to calculate the mean tensile strength for the fibre

  • It is important to ensure that the fibres are all of the same length and that all other variables are kept constant

Apparatus used to determine the tensile strength of plant fibres