Viscous Damping

It is encountered by bodies moving at moderate speed through liquid. This type of damping leads to a resisting force proportional to the velocity. The damping force

Fd ∞ dx/dt


Fd =cx


‘c’ is the constant of proportionality and is called viscous damping Co-eff. With the dimension of N-S/m

Types of Damping

1. Viscous Damping
2. Colomb Damping
3. Solid or structural Damping
4. Slip or Intrefacial damping

Vibrations

The study of vibration is concerned with the oscillatory motion of bodies and the forces associated with them. All bodies possesing mass and elasticity are capable of vibrating. Thus most enginerring machines and structure experience vibration to some degree and their design generally requires consideration of their oscillatory behaviour.

MEASUREMENT OF INTENSITY OF SOUND

The intensity of sound is defined as the quantity of energy propagating through a unit area per unit time, the direction of propagation being perpendicular to the area. The amount of power transmitted is measured in Watt/m². A convenient unit is microwatts/m².

According to Weber Fechner law in psychology, the loudness of a sound as judged by the ear is proportional to the logarithm of the intensity. If I1 and I0 represent the intensities ot two sounds of a particular frequency and L1 and L0 the corresponding measure of loudness then L1 = KlogI1 and L0=KlogI0. The difference in loudness technically known as intensity Level, L between them is given by

L = L1 – L2 =K[logI1 – logI0]

L = K log( I1 / I0 )

Where K is a constant that depends on the units and I0 is some standard reference intensity arbitrarily takes as 10

PROPAGATION OF SOUND

Sound is produced by a vibrating body.A material medium is necessary for the propagation of sound waves .In wave motion momentum and energy are transferred.Charactrestics of wave motion

1. Wave motion is a disturbance produced in the medium by the repeated periodic motion of the particles of the medium.

2. Only the wave travels forward whereas the particles of the medium vibrate about their mean position.

3. there is regular phase change between various particles of the medium. The particle ahead starts a vibrating a little later than the particles preceding it.

4. the velocity of the wave is different from the velocity with which the particles of the medium are vibrating about their mean position. The wave travels with a uniform velocity whereas the velocity of the particle is different at different positions. It is maximum at the mean position and zero at the extreme positions of the particles. There are two types of wave motions

a. Transverse wave

b. Longitudinal Wave

Sound waves are longitudinal waves and light waves are transverse waves. Figure 1 shows the formation and propagation of transverse and longitudinal wave.

A sound wave is propagated and conveyed to the ear by means of the intervening layers of air. Consider a vibrating tuning fork as shown in figure 2. Let us confine our attention to the right hand prong only. When it moves towards the right, it compresses the layer of air in front of it and as a consequence the pressure of this layer will be greater than the adjacent layers. It tends to relieve the strain thus created , by compressing them. These in turn hand on the compression. Thus a pluse of compression will travel onwards to the right. Again when the prong moves towards the left rarefraction are sent out in regular succession. These waves at last reach the ear and set the tympanic membrane, which is ultimately transmitted via a system of bones and cords to the brain and causes the mental sensation called sound

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Polymerisation

Polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymers chains. There are many forms of polymerization and different systems exist to categorize them.

Polymers such as PVC are generally referred to as "homopolymers" as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one molecule are referred to as "co-polymers".