Sound

SOUND AND LIGHT
GRADE 8

Vibration or osillation is periodic motion in which an object moves back and fort repeatedly about the equilibrium position. The diagram above shows a pendulum. A complete cycle (one vibration) occurs when force is applied and the bob swings from point K-L-M-L-K. Point L is the equilibrium point for this pendulumm

​​Vibration

Periode = T (second or s)
Frekuensi = f (hertz or Hz)
Amplitudo = A (the maximum displacement of an object from its equilibrium positions)
n = number of vibration
t = time for n number of fibration (second or S)

​​Quantity of Vibration

T = t/n
f = n/t
T = 1/f
f = 1/T

Waves

Waves is disturbance of matter that transfers energy and propagates through a mediaum. There are two types of waves, electromagnetic waves and mechanical waves. Another way to categorise waves is based on the direction of vibration of the particles relative to the direction of propogation of the wave, is transverse waves and longitudinal waves. Speed or velocity waves is the measure of how fast the wave propagates through a medium.

v = λ/T = λf

Sound

Sound waves, types of longitudinal wave. Sound cannot travel through a vacuum (empty space) because no particle to transfer the energy.

​Hearing Sound

We hear sounds when the sound waves reach our ears.

• pinna (daun telinga) is shaped to collect sound energy

• eardrum (gendang telinga) is a thin layer of tissue that separates the outer from the internal parts

• ossicles

• cochlea

  Ears are also important in our sense of balanced
  

​The Speed of Sound

The speed of sound is the distance sound waves travel in one second . Equation
v = d/t
v = speed (m/s)
d = distance sound wave travel (m)
t = time (s)
The speed of sound in air is approximately 340 m/s at 20^°.
The higher temperature of the air, the faster the sound travels.
In a liquid or a solid the particles are much closer together than in a gas.This means that the vibrations cen be passed onwards much faster. Sound waves travel the fastest in solids, then liquids and the slowest is in gas.

​Describing Sound

• Loudness

• Amplitude

• The rate at which sound energy passes through a unit area is called the sound intensity, measured W/m².

• intensity

• Doppler effect is the change of frequency of sound waves due to the relative motion between the source and observer.

• CRO (cathhode ray oscilloscope)

• Natural frequency

• Resonance

• L_n = λ/4 (2n - 1) for n = 1,2,3,4,....

• Echoes (gema)

• Sonar

​Resonansi

Reflection of Sound

Sonar

The same principle is used in sound navigation and ranging or "sonar" to detect underwater objects or sea bed. A device sends out ultrasound waves from a ship. The waves are reflected by objects.

Human ears can only detect sound of frequencies between 20 Hz and 20 000 Hzz

​Audible Sound

Is low frequency sound, less than 20 Hz. In nature, earthquakes, volcanoes, and avalanches are the sources of infrasound. Some animals such as elephants and giraffes.

Infrasound

Type of sounds

Is sound wave of frequencies above 20 000 Hz. Dolphins and bats use ultrasound very effectively to communicate and for echolocation

​Ultrasound

The Dangers of Sounds

Other loud noises can cause damage to our hearing over longer periods of time. For example, the ossicles (small bones) can wear out and become less sensetive as they rub together.
We can measure loudness with a sound meter in a unit called decibel (dB). The best way to protect your ears is to reduce the loudness of the noise around you, we can use ears protectors.

keep trying with a positive mindset