Midpoint (Equilibrium)

Crest (high point) Trough (low point)

 Sound is a fascinating phenomenon. When something vibrates in the atmosphere, it moves the air particles around it. Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air. Ourears pick up these fluctuations in air pressure and translate them into electrical signals the brain can process.Electronic sound equipment works the same basic way. It represents sound as a varying electric current.

 Any device that simply produces a better quality and more powerful version of the audio signal.

how often a vibration occurs (# of crests per second) vibrations per second

Heinrich Hertz demonstrated radio waves in The unit of frequency is the Hertz. 1 vibration per second = 1 Hertz Kilohertz = 1000 v/sec Megahertz = v/sec How does a radio work?

 Frequency and period are reciprocals of each other.  Frequency (f) = 1  period ◦ f = 1/T  Period (T) = 1  frequency ◦ T = 1/f

 Sound and light waves move.  As waves move, matter is NOT passed along them.

When you create a wave with a rope, it is the disturbance that moves along the rope, not the rope itself.

How fast a wave moves depends on the medium of the wave.

Wave speed is related to the frequency and wavelength of the wave. v = f* Wave speed (m/s) = frequency (Hz) X wavelength (m)

What is the speed of a wave with a frequency of 100 Hz and a wavelength of.025 meters?

v = fλ Speed = 100 Hz X.025 m Speed = 2.5 m/s How does satellite tv work?

Waves produced when the motion of the medium is at right angles (PERPENDICULAR) to the direction in which the wave travels. EX: Fishing bobber in a lake Fishing bobber in a lake

Waves produced when the particles move ALONG (PARALLEL) the direction of the wave rather than at right angles to it EX: Sound Waves Sound Waves

overlapping waves Interference Patterns Interference Patterns : patterns formed when waves overlap

1. constructive – reinforcing interference when waves align at the crests and troughs **individual effects are increased**

2. Destructive – cancellation interference Destructive when the crest of one wave aligns with the trough of another **their individual effects are reduced**

 Christian Doppler ( )  Change in frequency due to the motion of a sound source

Blue shift = frequency increases as it approaches Red shift = frequency decreases as it leaves

Higher frequency Lower frequency

A slower aircraft sends sound wave crests one at a time and we hear it as a continuous noise.

Chapter 26

Answer: vibrations

All sounds are made by the vibration of material objects.

A vibrating source sends a disturbance through a surrounding medium (such as air) in the form of longitudinal waves.

term that refers to how high or low sound appears to be Is it possible to shatter glass with your voice?

High # of vibrations = high frequency = high pitch EX: piccolo Lower # of vibrations = lower frequency = lower pitch EX: tuba

,000 Hz Ultrasonic – sound waves above 20,000Hz Infrasonic – soundwaves below 20 Hz Humans can hear the range from

 When a noise occurs, sound travels in all directions

Any medium that waves travel through; may be solids, liquids or gases Usually, sounds are emitted through air, but they can also pass through solids and liquids

 Solids and liquids are generally much better conductors of sound than air EX: ever heard motor boats under water?

 Sound travels MUCH slower than light EX: lightening and thunder  The speed of sound at room temperature is  340 m/s

Resonance Resonance – a phenomenon that occurs when the frequency of forced vibrations on an object matches the object’s natural frequency, and a dramatic increase in amplitude results

Resonance can occur in structures EX: marching over bridges swinging bridges by wind

Interference occurs in sound waves. Interference can occur “in phase” (constructive) or “out of phase” (destructive) EX: announcer at a football stadium Ripple Tank

Beat – periodic variation in the loudness of sound (different frequencies) EX: musical instruments out of tune Musical Beats

What is the beat frequency when a 400 Hz and a 405 Hz tuning fork are sounded together? Answer: Change in frequency = 5 Hz Therefore, the beat frequency is 5 beats per second

Chapter 27

 we see objects because light bounces off them  Light is energy that is emitted by vibrating electric charges in atoms that travel in waves

Speed of light = extra distance traveled extra time measured = 300,000,000 km / 1000 sec = 300,000 km/sec

light year – the distance traveled by light in one year ≈ 9.5 x km

 Waves by which light energy travels  All are radiated by vibrating electrons within an atom

Light waves are transverse waves. Polarization – the filtering out of all vibrations in a transverse wave, such as a light wave, that are not in a given direction

 Reflection – bouncing off  Refraction – penetrating (goes through) and bends