About Plastics

What is Plastic?

Plastic is a polymer in which monomers are arranged in linear or cross linked chains.

Alexander Parkes is the creator of first plastic known as “Parkesine”.

Types of Plastics:

a) Thermoplastic 

This is the plastic which gets deformed easily by heating. Some of the thermoplastics are polythene and PVC. This is a plastic which will soften when heated and harden when cooled. Thermoplastic is a polymer that turns into a liquid when heated and freezes to a glassy state when cooled sufficiently.

b) Thermosetting Plastics 

These are the plastics which moulded once cannot be softened/deformed by heating. Bakelite and Melamine are such plastics.

 Properties of Plastics

1.  Plastics are easily mouldable into different shapes.
2. Plastics could be recycled.
3. Plastics could be melted.
4. Plastics could be rolled into sheets.
5. Plastic could be drawn into wires
6. Plastics are nonreactive to chemicals and atmosphere.
7. Plastics are light in weight
8. Plastics are cheaper than metals.
9. Plastics are poor electric conductors and could be used as insulators.
10. Plastics are poor thermal(heat) conductors and hence could be used for cooking utensils etc.

Biodegradable and non-biodegradable Plastics

Plastics, which are decomposed by natural process through bacteria in the presence of water, sunlight and oxygen are called bio-degradable plastics.   Plastics which cannot be decomposed by natural processes are called non-biodegradable plastics.

Plastics take long time for decomposition which causes pollution of environment. Burning of plastics causes poisonous fumes into air.

SOUND - Important Notes

1. A vibrating body produces sound.
2. Sound has energy
3. Sounds are produced by vibrating bodies and the air that passes through orifices of the instruments.
4. Sound needs a medium to propagate.
5. The to and fro motion of a body from its mean position is known as one vibration.
6. The maximum displacement of vibrating body from its mean position is called as amplitude.
7. The number of vibrations per second is called as frequency.
8. The shrillness of a sound is known as pitch.
9. The pitch of the sound depends upon its frequency.
10. Normal sound consists of mixed frequencies.
11. The sounds which are pleasant to hear are called as music. Music is a combination of sounds that are produced in an order and pleasant to hear.
12. The sounds which are unpleasant to hear are called as noise.
13. The sounds that a normal human being can hear are called as audible sounds.
14. The sounds that a normal human being cannot hear are called inaudible sounds.
15. Frequency of the audible sounds ranges from 20 Hertz (20 vibrations/sec) to 20000 Hertz(20000 vibrations/sec).