Solids: crystalline, amorphous and mechanical properties
Answers are for parents and teachers.
1
A 5 m wire is stretched by 2.5 mm. Find ε (in per cent).
ε = 0.0025/5 = 5·10⁻⁴ = 0.05 %
2
A force of 800 N acts on a wire of cross-section 4 mm². Find the stress in MPa.
200
3
In a steel wire (E = 2·10¹¹ Pa) the stress is 2·10⁸ Pa. Find ε.
ε = σ/E = 10⁻³
4
Are the particles at the lattice nodes motionless? Explain.
No, they vibrate about the node but do not leave their place.
5
Give two everyday examples of elastic deformation.
For example a spring and a football: the shape recovers when the force is removed.