Sound Elaine S. Vejar NSF GK-12 Fellow-Vibes and Waves in Action Center for Advanced Computation and Telecommunications Department of Biomedical Engineering and Biotechnology University of Massachusetts-Lowell

Sound Sound is created when molecules in a medium are made to vibrate by a vibrating source (Ex: your vocal chords, a speaker, or movement of a guitar string) Vibrations are transferred by the air molecules from one region to the next in the form of a pressure wave. Compressions cause high pressure points and Expanding regions (rarefactions) create lower pressure points in space Pressure wave travels at a certain speed: Speed of sound in air: 330 meters/sec. When an object moves back and forth, or vibrates, it pushes the air molecules next to it. As air molecules get compressed into waves, the energy is transferred from molecule to molecule until it is exhausted. That is why sounds that are farther away sound softer — their energy fades as they travel. National Institute on Deafness and Other Communication Disorders

Waves in Space If you plot the change in pressure in space, the shape of the wave looks as shown in the figure below. This is a periodic function: The shape repeats at a distance equal to the ‘wavelength’ : Distance from one crest to the next in meters : L meters The time taken by the wave to travel from one crest to the next is T seconds: Therefore speed of the sound wave C = distance travelled / Time =L/T The distance from the midpoint to the crest of a wave

Waves in Time T : Time Period F : 1/ T ( Hertz) If you stand in one place and measure the pressure variations in time, the shape is as shown here. This is also a periodic function that repeats every ‘T’ seconds 1 Cycle : One complete up and down movement : Takes T seconds T : Time Period Frequency : Number of cycles per second (Hertz) F : 1/ T ( Hertz)

It is known that speed of sound in air is approximately 330 meters/second Lets calculate: How long does it take for a sound wave to travel 5 feet? : t seconds Distance D = 10 meters v= 330 = D/t  t = D/330 = ??? Seconds Let’s Find out

Measuring Sound Sound intensity: Sound intensity is the rate at which energy is being carried by a sound wave through a given area.(W/m²). More Energy moves more molecules Louder Sound Less Energy moves fewer molecules Softer Sound Sound level: Loudness of sound measured in decibels (dB) More energy, higher amplitude. Humans can hear sound at a range from 20 Hz to 20,000 Hz

Human Hearing

Noise or Music Noise Music just random, disorganized sounds. organized into patterns that have pitch and rhythm Pitch: refers to how high or low sound frequencies appear to be Rhythm: recurring at regular intervals

Sound Conduction Sound travels in any medium, except a vacuum.

Tuning Fork Station Keyboard and Oscilloscope Experiment Stations Tuning Fork Station Keyboard and Oscilloscope