Waves & Sound 8 th - Grade

Wave – Repeating disturbance or movement that transfers energy through matter or space. – Ex. Ocean waves, microwave waves, radio waves, light waves, Medium – Matter the waves travel through; can be solid, liquid, gas or a combination of these. – Sound travels fastest through solid medium. Mechanical Waves – Waves that travel only through matter. – Seismic, transverse and compressional

Transverse waves – Matter in which the medium moves back and forth at right angles to the direction that the wave travels. – Ex. Shaking one end of a rope while your friends hold the other end.

Compressional Waves – Matter in the medium moves back and forth along the same direction the wave travels. – Ex. Coiled Spring Toy Compression Area of a sound wave Where particles are squeezed Close together

Wave Properties Parts of a Wave – 1) Crests Alternating high points of transverse waves – 2) Troughs Alternating low points of transverse waves – 3) Rarefaction Less-dense region of a compressional wave

Wave Properties 4) Wavelength – The distance between one point on a wave and the nearest point just like it. – In a compressional wave the wavelength is the distance between two compressions or two neighboring rarefactions. – In a transverse wave the wavelength is from crest to crest or trough to trough.

When you tune your radio to a station, you are choosing radio waves of a certain frequency. Frequency – Number of compressions that pass a point each second. – Expressed in hertz (Hz). – A frequency of 1 Hz means that one wavelength passes by in 1 second. Period – Amount of time it takes one wave length to pass a point. Expressed in seconds. – As the frequency of a wave increases, the period decreases.

Calculating Wave Speed Speed = frequency x wavelength You will have to calculate speed, frequency and wavelength on your test!

Amplitude – The distance from the top of the crest to the rest position. – Related to the energy carried by a wave. – The greater the wave’s amplitude is, the more energy the wave carries. Intensity – The amount of energy that flows through an area in a certain amount of time.

Destructive – Type of interference that results in two waves canceling each other out.

Constructive – The type of interference that occurs when two wave crests arrive together.

Sound The study of sound! – Acoustics 1 unit of sound intensity – Decibel Pitch – The highness or lowness of sound Sound that has no set pattern or definite pitch – NOISE Sounds with specific pitches and qualities that follow a regular pattern- MUSIC

Sound Reverberation – The effect produced by the many reflections of sound.

Sound Resonance – The ability of an object to vibrate by absorbing energy at it’s natural frequency. Quality – Describes the difference between two sounds of the same pitch and loudness

Anatomy of the Ear

The 3 bones of the middle ear in order from the eardrum inwards – 1) hammer (malleus) – 2) anvil (Incus) – 3) stirrup (stapes) Another name for the eardrum ? – Tympanic membrane

A healthy human ear can hear frequencies ranging between 20-20,000 Hz Ultrasonic – Frequencies that are too high pitched for the human ear to hear The pain threshold is reached and hearing loss may occur if a human ear is exposed to a sound of 120dB for an extended period of time.