# Ask a Teacher

## Applications of Elasticity

1. Most parts of structures and machinery are under some kind of stress. In their design, it has to be ensured that applied stresses do not exceed the elastic limits of the materials.
2. Due to particular elastic properties, some materials are used as vibration absorbers. For example, some types of rubber have particularly large hysteresis loops and so are useful as vibration absorbers. If a block of such a rubber is placed between a piece of vibrating machinery and the floor, much of the energy of the mechanical vibrations is converted to heat energy in the rubber and so is not transmitted to the floor.
3. In a car, it is desirable that as little heat is generated as possible. For this reason, in the manufacture of car tyres that rubber is used which has small hysteresis loop.
4. Because of its strength and elastic properties, steel is used to make not only springs but in the construction of girders as well.
5. The cross-section of steel girders has the form of the letter I. Most of the material in these I-beams is concentrated in the top and bottom flanges; the piece joining the flanges, called the web, is of thinner cross-section. Thus when the beam is used horizontally in construction, the stress is predominantly in the top and bottom flanges - not in the central portion. One flange is squeezed while the other is stretched. Between the top and bottom flanges is a stress-free region that acts principally to connect the top and bottom flanges together. This is the neutral layer where comparatively little material is needed. The flanges carry virtually all stresses in the beam. An I-beam is nearly as strong as a solid rectangular bar of the same overall dimensions, and its weight is considerably less. A large rectangular steel beam on a certain span might collapse under its own weight whereas an I-beam of the same depth would carry much added load.
6. A hollow shaft is stronger than a solid shaft made of same equal material. It is because the torque required to produce a given twist in a hollow shaft is greater than that required to twist a solid shaft of the same length and material through the same angle. For this reason, electric poles are made hollow.