Sound by 2E1 Aziizah

What is sound?
Sound is the quickly varying pressure wave within a medium. We usually mean audible sound, which is the sensation (as detected by the ear) of very small rapid changes in the air pressure above and below a static value. This "static" value is atmospheric pressure (about 100,000 Pascals), which does nevertheless vary slowly, as shown on a barometer. Associated with the sound pressure wave is a flow of energy. Sound is often represented diagrammatically as a sine wave, but physically sound (in air) is a longitudinal wave where the wave motion is in the direction of the movement of energy. The wave crests can be considered as the pressure maxima whilst the troughs represent the pressure minima.

ii. How is sound being produced?
Sound is produced when the air is disturbed in some way, for example by a vibrating object. A speaker cone from a high fidelity system serves as a good illustration. It may be possible to see the movement of a bass speaker cone, providing it is producing very low frequency sound. As the cone moves forward the air immediately in front is compressed causing a slight increase in air pressure, it then moves back past its rest position and causes a reduction in the air pressure (rarefaction). The process continues so that a wave of alternating high and low pressure is radiated away from the speaker cone at the speed of sound.

iii. What affects sound?
Vibrations and frequency affects sound. Vibrations produce sounds. When objects vibrate, they move backwards and forwards very quickly. The number of vibrations in one second is called the frequency.

iv. Examples of stuff producing sound?
Drums
Guitar
Bee
Trumpet
Saxophone

Summary:
Sound is a form of energy.
The vibration of objects produces sounds.
Frequency is the number of vibrations per second. Frequency is measured in hertz {Hz).

Sources:
http://www.tek-ltd.com/school2.htm