Deaf - unable to hear sounds

Decibel - a unit to measure sound intensity (volume); it is abbreviated as dB

Echo - the bouncing or reflection of a sound wave from an obstructing surface

Frequency - the number of sound vibrations per second; frequency determines pitch which is the highness or lowness or a sound;
the faster an object vibrates, the sound it emits will have a higher pitch, the slower an object vibrates, the sound it emits will have a lower pitch.
Therefore, whatever causes an object to vibrate faster or slower, will change the pitch of the sound it makes. For example, a guitar string which is thicker, vibrates slower and will have a lower pitch. A guitar string which is thin will vibrate faster and have a higher pitch. The other way to make a guitar string vibrate slower or faster is by 'shortening' or 'lengthening' it. This is easily done by pressing your finger onto the string which is, in effect, shortening it. A shorter string vibrates faster and will have a higher pitch. Letting go of the string is, in effect, 'lengthening' the string. A 'longer' string will vibrate slower and have a lower pitch.

Inner Ear - inside the ear is a coiled tubed called the cochlea; the cochlea is filled with fluid and nerve endings

Loudspeaker - something that converts electrical energy to sound

Megaphone - a funnel (cone) shaped device for amplifying or directing sound

Microphone - an instrument that converts sound waves into electrical energy

Middle Ear - three tiny bones (hammer, anvil, stirrup) that form a bridge between the eardrum and the inner ear.

Noise - sound produced by irregular vibrations in which the sound waves have no smooth pattern; any sound that is considered unwanted, unpleasant or too loud

Outer Ear (pinna) - visible part of the ear which is made of skin and cartilage.

Pitch - the highness or lowness of a musical note; different pitches have different frequencies

Reflection - a sound wave that is bounced off an object as in an echo

Sound - the transfer of molecular vibrations from an originating source within any medium (gas, liquid or a solid); these vibrations can be perceived through touch or your ear

Sound waves - vibrations of molecules transferred in ''waves'' through either a gas, liquid or solid;
in order for sound to exist, molecules must be present and the molecules must have a source which starts them to vibrate - passing their vibrations outward and in successive waves. In a vacuum (like in outer space), sound cannot be produced nor transferred.

Stethoscope - an instrument used by doctors to listen to sounds made by the heart and lungs

Tension - the condition of being stretched between two points

Vibrations - movements backwards or forwards OR up and down

Wavelength - one full wave movement, such as from the crest of one wave to the crest of the next