1. Important Terms Chapter 26 April 21, 2014

2. Important Concepts Sound Transmission (What is Needed?) – A source of vibration – A Medium to transport the energy via compression and rarefaction (expansion) – Types of Mediums: Solid, Liquid, Gas Solids: Metals, Wood, Rock (Steel, Iron, Brass) Liquids: Water, Oil, Milk Gases: Air, Nitrogen, Helium

3. Definitions Compression: A pulse of compressed air (air particles squeezed together) or other matter. The opposite of rarefaction. Rarefaction: A disturbance in the air (or matter) in which the pressure is lowered. The opposite of compression. http://www.youtube.com/watch?v=zKwpv8mZHRM http://www.youtube.com/watch?v=GkNJvZINSEY http://www.youtube.com/watch?v=L4F4zaRqQdk http://www.youtube.com/watch?v=qgdqp-oPb1Q

4. Definitions Vibration: An oscillation, a repeating back and forth motion about an equilibrium. Frequency: The number of events (cycles, vibrations, oscillations or any repeated event) per unit time measured in Hertz (or events per unit time) Hertz: The SI unit of frequency, One hertz (Hz) ids one vibration (cycle) per second. Pitch: The term that refers to how high or low in FREQUENCY a sound wave is.

5. Definitions Sonic: Sound waves that are between 20 Hz and 20,00 Hz or the normal range of frequencies that the human ear can detect. Infrasonic: Sound waves that are BELOW 20 Hz. Ultrasonic: Sound waves that are ABOVE 20,000 Hz. Most people cannot hear sound below 20 Hz nor above 20,000 Hz but many animals can hear above 20 KHz.

6. Definitions Amplitude: The distance from the midpoint to the maximum (Crest or peak) of a wave or equivalently, from the midpoint to the minimum (trough or valley). Loud or Soft: The terms that refer to the magnitude of the amplitude of a sound wave. Sound Intensity: Proportional to the square of a sound’s amplitude

7. Definitions Forced Vibration: The act of deliberately causing an object to vibrate using the vibrations of another vibrating object as the stimulus. An instrument sounding board is an example. Natural Frequency: A frequency at which an elastic object, once energized, will vibrate. Minimum energy is required to continue vibration at this frequency. It is also known as the Resonant Frequency

8. Definitions Resonance: The phenomenon when the frequency of a forced vibration on an object (excitation frequency) matches the object’s natural frequency resulting in a dramatic increase in wave amplitude. Why? What is occurring? Two waves are adding in-phase thereby adding constructively

9. Definitions Beats: A throbbing variation in the loudness of sound caused by interference when two tones of slightly different frequencies are sounded together. The perceived frequency of the “throbbing” is known as the Beat Frequency. http://www.youtube.com/watch?v=oAfxkCAyFhw http://www.youtube.com/watch?v=sTNwjTZJ-sc http://www.youtube.com/watch?v=4Tno4L-6vP4