1. The Young Modulus Objectives: Define and use the terms stress, strain and Young Modulus Describe an experiment to determine the Young Modulus of a metal wire.

2. The Young Moduls How elastic or stiff a material is

3. Example Steel cables over 1 m in diameter support a suspension bridge. The load of the bridge causes a tensile force in the cable, setting up a tensile stress. This has the effect of stretching the cable, setting up a tensile strain.tensile forcetensile stresstensile strain In addition to the cable being elastic and strong, it must be stiff.elastic strongstiff The material property (constant) which tells us how stiff it is within its elastic limit is called the Young Modulus, E, where: E = tensile stress tensile strain Unit: N m -2 or Pascals (Pa)

4. Stress Stress = Tensile Force cross sect. area Or,  = F/A Units N m -2 or Pascals (Pa) Strain = extension of wire original length No units as it is a ratio

5. Measuring the Young Modulus Method Set up the equipment as shown. Measure the diameter with a micrometer (at 5 places along the wire – then calulate average) Measure the initial length of the test wire Add kilogram masses 1 by one and measure the extension using a vernier calliper (or micrometer scale) Make a table of Tensile Force and extension (make repeat measurements)

6. Analysis Draw a graph of extension against Tensile Force Work out the gradient (e/F) Work out the inverse of the gradient (F/e) Now use the equation: Young Modulus = Stress/Strain to work out the Young Modulus Check with a reference book