We hear a sound when something vibrates.
Vibration – 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 – How high or low a sound is eg. Whistle – high pitched
and a cow mooing – low pitched.
Intensity – Loudness or softness of a sound,
measured in decibles. (DB)
Frequency of a sound – Speed at which the object vibrates. Low frequency produces a low pitch. High frequency produces high pitch. 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.
Kind of sounds: Whisper 15 decibels
Soft music 30 decibels
Normal house sound 45 decibels
Conversation 65 decibels
Heavy Street traffic 75 decibels
Thunder 110 decibels
Painful sound noise 120 decibels
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.
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).
When you blow across a bottle, the air in the bottle vibrates. Where 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 because the water is vibrating to create the sound.
A long object has a lower pitch because it vibrates slowly, while a short object has a high pitch because it vibrates quickly.
Note: Rubber bands of the same size and thickness will produce a different pitch when stretched to various lengths or plucked.
When rubber bands are of the same length and different thickness. The thicker band will produce a lower pitch.
Noise is produced by irregular vibrations. These vibrations are unpleasant to the ear. A lawnmower in operation or a loud sound system can produce unpleasant sounds. Unpleasant sounds are called noises.
Using thick curtains, rugs and Styrofoam in the ceilings will reduce noise pollution as these materials will absorb sound.
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.