Sound

 

 
 
We hear a sound when something vibrates.
 
Vibration is the back and forth movement of sound waves.
 
When vibrations are regular we get a pleasant sound. Eg- Music.
 
When vibrations are irregular they produce noise such as a very loud boom box, sound system or a lawnmower.
Pitch of a sound is How high or low a sound is :
Whistle – high pitched
cow mooing – low pitched.
Intensity of a sound – Loudness or softness of a sound, measured in decibles. (DB)
 
Types of sounds and their intensity 
Whisper 15 DB
Soft music 30  DB
Normal house sound 45 DB
Conversation 65 DB
Heavy Street traffic 75 DB
Thunder 110 DB
Painful sound noise 120 DB
 
Frequency of a sound – This is the speed at which the object vibrates.
Low frequency produces a low pitch.  Sound waves are wide and long.
High frequency produces high pitch. Sound waves are short and narrow.
Frequency is measured in hertz;

you can change the frequency by changing the tightness, thickness or length of a string. On a guitar if you tighten the strings, you increase the pitch. If you loosen the strings, you lower the pitch. Short and thick produce the lowest when plucked. Long and thin strings produce the highest pitch when plucked.

 
The vocal chord vibrates as air passes over them.
 
Your vocal chords are located inside your voice box or larynx. The windpipe (trachea) is the tube through which you breathe.
 
How does sound travel
Sound travels in waves from the source outwards in all directions.
Sound must have a medium to travel through, such as solids, liquids and gases. Sounds cannot travel across an empty space or vacuum. Sounds travel at different speeds, but fastest through solids. This is because the particulars in solids are packed very closely together causing faster collisions among the particles.
Sound travels slowest through gases because the particles are far apart. When we speak on a telephone sound travels across the cable (solid)
 
High pitched and low pitched sounds
When you blow across a bottle, the air in the bottle vibrates. There is a small amount of water then the air column is longer. A lot of water means the air column is shorter.
A short air column will cause the vibration to be fast and the pitch high. A long air column will cause the vibration to be slower and the pitch lower. However, if you hit the bottle, the bottle with the least water and longer air column will vibrate fastest and produce a high pitch. A long object has a lower pitch because it vibrates slowly, while a short object has a high pitch because it vibrates quickly.
 

Key Questions- Discuss with your classmates

 

• Part 1:
  • Which bottle will produce the highest pitch if we tap the bottle with a spoon? Which bottle will produce the lowest pitch?
  • How do the bottles differ between the highest pitch to the lowest pitch?
• Part 2:
  • Which bottle will produce the highest pitch if we blow across the top of the bottle?
  • Which bottle will produce the lowest pitch?
  • How do the bottles differ between the highest pitch to the lowest pitch?
  • Why does blowing across the top of the bottle and tapping the bottle produce different sounds? (Hint: Think about which medium is being vibrated in each case.)

Note: Rubber bands of the same size and thickness will produce a different pitch when stretched to various lenghts or plucked.
When rubber bands are of the same length and different thickness. The thicker band will produce a lowest pitch.
The shorter the length of an object the higher the frequency and the higher the pitch
The longer the length of an object the lower the frequency and the lower the pitch
 

Noise Pollution
Noise is produced by irregular vibration. These vibrations are unpleasant to the ear. A lawnmower in operation or a loud sound system can produce unpleasant sounds. Unpleasant sound we call noises.
Preventing noise pollution in the home.

• Using thick curtains, rugs and Styrofoam in the ceilings will reduce noise pollution as these materials will absorb sound.

Echo
Sound waves are reflected (bounced back) by smooth hard surfaces such as a wall and this produces an echo. If the object is soft like a cushion or carpet the sound is absorbed and will not bounce back. Echo sounding is the use of sound to detect or locate an object by its echoes. Eg.bats.