Class 2 Writting

Sound is a form of energy. For sound to be produced vibrations must be set up by a source.  This is done by hitting (drum), blowing (recorder), stroking (sand paper on wood) and electrical (loudspeaker).

The vibrations travel through a solid liquid or gas and reach our ears where it can be heard.  If the vibrations have a lot of energy then they are loud.  If they have little energy then the sound is quiet.  Sometimes the vibrations can be seen or felt on the skin.

In air, sound travels at 1,160 km per hour, but speeds up in water to 5, 400km per hour.  Things which travel faster than sound are called supersonic.  The Concorde can travel faster than sound.

Dolphins communicate with each other under the sea.  The sound can travel for hundreds of miles, much further than in air.  Sound travels even more quickly through a solid metal than through the air or water.  Standing near a railway line, a humming from the rails can be heard several minutes before a train itself can be heard directly.  

Sound travels through solids and liquids as well as air.  Sound cannot travel through a vacuum.  Sound travels at different speeds in different substances.  This is because different substances are made up of particles in different ways.  The sound pushes the particles and as it travels it moves from one particle to another.  In a gas the particles are far apart, so some of the sound energy is lost when trying to push one particle into another one. Therefore the speed of sound is slow so it will not travel as fast as it does in substances where the particles are closer together.

Pitch is the highness or lowness of a sound.  A high pitch is caused by short vibrations and a low pitch is caused by long vibrations.

The pitch of a note produced by a guitar depends on the length, thickness and tension of the string.  A shorter, thinner, tighter string produces a high pitch and a longer, thicker, looser string produces a low pitch. On a guitar the strings can be shortened by putting a finger on the fret board.

In a wind instrument a column of air is set vibrating and the pitch depends on the length of the column.  A long column makes a low pitch and a short column makes a high pitch.

The loudness (volume) of the sound depends on the amount of energy the vibrations contain and the rate at which this energy is transmitted.